The present application claims priority under 35 U.S.C. §119to Japanese Patent Application No. 2014-030694, filed Feb. 20, 2014. The contents of this application are incorporated herein by reference in their entirety.
The present disclosure relates to a photosensitive member refreshing device and an image forming apparatus.
A photosensitive drum (photosensitive roller) in an electrophotographic image forming apparatus has a photosensitive layer on a surface thereof. Photosensitive layers are categorized as organic photosensitive members, selenium arsenic photosensitive members, amorphous silicon photosensitive members, or the like according to their principal components. The organic photosensitive members are relatively inexpensive but need to be replaced frequently as being susceptible to wear. The selenium arsenic photosensitive members have a longer life as compared with the organic photosensitive members but are difficult to handle as including a toxic substance. The amorphous silicon photosensitive members are harder, more resistant to wear deterioration, and easier to handle as being harmless substances. Therefore, amorphous silicon photosensitive drums are insusceptible to deterioration of properties of their photosensitive layers and allow maintenance of high image quality even after prolonged usage. Thus, the amorphous silicon photosensitive members are advantageous in terms of environmental friendliness and prevention of cost increase, and therefore the demand for amorphous silicon photosensitive drums has been increasing recently.
Meanwhile, photosensitive drums can be a cause of a phenomenon referred to as image deletion. The image deletion is the phenomenon that describes occurrence of a blurred image or an edge stagnant image. The image deletion occurs because discharge products such as a nitric acid ion and an ammonium ion produced through discharge from a conductive member attach to a surface of a photosensitive drum, and the discharge products are ionized in a high humidity environment to partially reduce the surface resistance of the photosensitive drum. An electrostatic latent image formed on a film having a reduced surface resistance runs outward to cause potential drop. As a result, the boundary of the electrostatic latent image becomes unclear, leading to the image deletion.
The image deletion occurs pronouncedly in an image forming apparatus including an amorphous silicon photosensitive member. This is because the amorphous silicon photosensitive member has a surface that is insusceptible to wear with a blade (cleaning blade) or the like, and the surface easily absorbs moisture.
In a known technique, therefore, aging is performed on a photosensitive drum prior to image formation in order to prevent the image deletion. The aging is to grind and remove discharge products deposited on the surface of the photosensitive drum. Some image forming apparatuses vary the duration of the aging according to the degree of the image deletion.
A photosensitive member refreshing device according to the first aspect of the present disclosure includes an image bearing member, an exposure device, a developing device, a detecting section, a cleaning section, and a control section. The image bearing member has a photosensitive roller rotatable about a rotation axis. The exposure device exposes the photosensitive roller to light according to an exposure pattern. The developing device supplies a toner to the photosensitive roller to form a toner image corresponding to the exposure pattern on the photosensitive roller after the exposure device has exposed the photosensitive roller to light. The detecting section detects the toner image on the image bearing member. The cleaning section cleans a surface of the photosensitive roller. The control section controls the exposure pattern based on a result of detection by the detecting section.
An image forming apparatus according to the second aspect of the present disclosure includes a photosensitive member refreshing device according to the first aspect of the present disclosure and an image forming section. The image forming section forms an image on a sheet.
Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the same reference numerals denote the same or equivalent elements in the drawings, and the description thereof will not be repeated.
(Basic Principle)
The basic principle of a photosensitive member refreshing device 1 according to the first embodiment of the present disclosure will be described with reference to
The photosensitive member refreshing device 1 includes an image bearing member 10, an exposure device 40, a developing device 20, a detecting section 50, a cleaning section 30, and a control section 80. The image bearing member 10 has a photosensitive roller 11 rotatable about a rotation axis and an intermediate transfer belt 15. The exposure device 40 exposes the photosensitive roller 11 to light according to an exposure pattern. The detecting section 50 detects a toner image on (transferred onto) the image bearing member 10.
According to the first embodiment, the exposure pattern of the exposure device 40 is controlled based on the result of the detection by the detecting section 50, and a toner image corresponding to the exposure pattern based on the result of the detection is formed on the photosensitive roller 11. For example, the exposure device 40 performs exposure in the exposure pattern so that more toner is supplied to a region where the image deletion has occurred. As a result, the cleaning section 30 can clean the photosensitive roller 11 using an appropriate amount of toner. That is, the developing device 20 can supply the toner selectively to the region where the image deletion has occurred.
In the present specification, a direction along the rotation axis of the photosensitive roller 11 is defined as a main scanning direction, and a direction perpendicular to the main scanning direction is defined as a sub-scanning direction. A dimension along the main scanning direction is defined as a width, and a dimension along the sub-scanning direction is defined as a length.
(Photosensitive Member Refreshing Device 1)
The photosensitive member refreshing device 1 will be described with reference to
The intermediate transfer belt 15 is an endless belt and rotates in a rotation direction D. The photosensitive rollers 11 are disposed on the outer circumferential surface of the intermediate transfer belt 15 and rotate in a rotation direction R. The primary transfer rollers 12 are disposed facing the respective photosensitive rollers 11 via the intermediate transfer belt 15. The developing devices 20, the cleaning sections 30, and the exposure devices 40 are disposed around the respective photosensitive rollers 11.
Each of the exposure devices 40 irradiates the corresponding photosensitive roller 11 with light to form an electrostatic latent image corresponding to the exposure pattern on the surface of the photosensitive roller 11. The developing devices 20 supply the toners onto the respective photosensitive rollers 11. Each of the toners supplied from the developing devices 20 onto the photosensitive rollers 11 attaches to the electrostatic latent image formed on the corresponding photosensitive roller 11. As a result, a toner image corresponding to the electrostatic latent image is formed on the surface of each photosensitive roller 11.
Each of the photosensitive rollers 11 has a cylindrical substrate and a photosensitive layer having a thickness of 10 μm to several tens of μm formed on a surface of the substrate. The primary transfer rollers 12 transfer the toner images formed on the surfaces of the respective photosensitive rollers 11 onto the intermediate transfer belt 15. The toner images are superimposedly transferred from the respective photosensitive rollers 11 to the outer circumferential surface of the intermediate transfer belt 15.
The cleaning sections 30 continue to rotate in a specified direction after the transfer of the toner images from the photosensitive rollers 11 to the intermediate transfer belt 15 thereby to rub the surfaces of the respective photosensitive rollers 11. The cleaning sections 30 clean the surfaces of the respective photosensitive rollers 11 by rubbing the surfaces of the photosensitive rollers 11 and removing toners remaining thereon. The cleaning sections 30 also clean discharge products deposited on the surfaces of the respective photosensitive rollers 11 by rubbing the surfaces with the remaining toners.
In the present embodiment, the detecting section 50 detects the toner images transferred onto the intermediate transfer belt 15. The control section 80 controls each of the exposure devices 40 to perform exposure in a cleaning pattern based on the result of the detection by the detecting section 50.
The cleaning of the toner images developed on the photosensitive rollers 11 by the cleaning sections 30 is referred to as refreshing. Specifically, the cleaning pattern exposure by the exposure devices 40 and the subsequent cleaning of the toner images formed on the surfaces of the photosensitive rollers 11 by the cleaning sections 30 are referred to as refreshing. The refreshing is performed before or after image formation.
Next, the photosensitive member refreshing device 1 will be described in detail with reference to
Each of the cleaning sections 30 includes a cleaning blade 31, a friction roller 33, and a toner collecting roller 35. Each of the cleaning blades 31 is fixed in contact with the corresponding photosensitive roller 11. Each of the friction rollers 33 is disposed so as to be in pressed contact with the corresponding photosensitive roller 11. Each of the toner collecting rollers 35 is disposed adjacent to the corresponding friction roller 33.
The cleaning blades 31 remove toners remaining on the surfaces of the respective photosensitive rollers 11. The friction rollers 33 are driven to rotate in a rotation direction Q while being pressed against the respective photosensitive rollers 11 at a predetermined pressure. While rotating, the friction rollers 33 remove the toners remaining on the surfaces of the respective photosensitive rollers 11 at interfaces between the friction rollers 33 and the photosensitive rollers 11, and rub the surfaces of the photosensitive rollers 11 for cleaning. The toner collecting rollers 35 rotate in a direction opposite to the rotation direction Q of the friction rollers 33 while being in contact with the surfaces of the respective friction rollers 33 thereby to collect the toners on the friction rollers 33. The toners collected are dropped into a residual toner conveyance path disposed below the cleaning sections 30 and recovered.
Each of the assemblages has a charger 60 including a charging roller 65 and a cleaning brush 67. The chargers 60 uniformly charge the surfaces of the respective photosensitive rollers 11. Each of the charging rollers 65 is disposed in contact with the corresponding photosensitive roller 11 and driven to rotate by the rotation of the photosensitive roller 11. Each of the charging rollers 65 applies a voltage to the surface of the corresponding photosensitive roller 11 so that the surface of the photosensitive roller 11 is uniformly charged. Each of the cleaning brushes 67 is disposed under the corresponding charging roller 65 and driven to rotate by the charging roller 65. The cleaning brushes 67 remove unwanted matters such as toners on the surfaces of the respective charging rollers 65.
The detecting section 50 will be described with reference to
The sensor is for example a contact image sensor. The contact image sensor has an image sensor and an array of lenses with the same magnification. Since the contact image sensor has the array of lenses with the same magnification, the distance from an object being detected to the image sensor is short. Accordingly, a space for disposing the detecting section 50 can be small. The contact image sensor may further have a light source as needed.
The toner images will be described with reference to
It is noted here that a shorter exposure pattern length on the photosensitive rollers 11 is more likely to cause image deletion, while a longer exposure pattern length is less likely to cause image deletion. Accordingly, each toner image is formed from an image having a longer length and an image having a shorter length. As a result, the detecting section 50 can detect and compare densities of the images, and thus detect whether or not image deletion has occurred.
The length L of the thick line KA is longer than the length of each of the thin lines KB. Accordingly, the detecting section 50 can detect whether or not image deletion in black has occurred by comparing the density of the thick line KA and the density of the thin lines KB. Whether or not image deletion in cyan, magenta, and yellow has occurred can be detected in the same manner.
The relationship between the toner image length and the luminance value will be described with reference to
First, the relationship between exposure patterns and the surface potential in the case of normal toner image formation (no image deletion) and in the case of image deletion will be explained with reference to
The difference between the surface potential in the case of image deletion and the surface potential in the case of normal toner image formation is greater when the exposure pattern length is D2 than when the exposure pattern length is D3. The diagram therefore indicates that the surface potential in the case of image deletion is more unclear in the boundary of the exposure pattern when the exposure pattern length is D2 than when the exposure pattern length is D3. In addition, the difference between the surface potential in the case of image deletion and the surface potential in the case of normal toner image formation is greater when the exposure pattern length is D1 than when the exposure pattern length is D2. The diagram therefore indicates that the surface potential in the case of image deletion is more unclear in the boundary of the exposure pattern when the exposure pattern length is D1 than when the exposure pattern length is D2. That is, the diagram indicates that in the case of image deletion, the shorter the exposure pattern length is, the greater the difference between the boundary of the surface potential and the exposure pattern is, and the more unclear the boundary of the surface potential is.
Next, the relationship between the toner image luminance value and exposure patterns in the case of normal toner image formation and in the case of image deletion will be explained with reference to
The difference between the toner image luminance value in the case of image deletion and the luminance value in the case of normal toner image formation is greater when the exposure pattern length is L2 than when the exposure pattern length is L3. The diagram therefore indicates that the luminance value in the case of image deletion is more unclear in the boundary of the exposure pattern when the exposure pattern length is L2 than when the exposure pattern length is L3. In addition, the difference between the luminance value in the case of image deletion and the luminance value in the case of normal toner image formation is greater when the exposure pattern length is L1 than when the exposure pattern length is L2. The diagram therefore indicates that the luminance value in the case of image deletion is more unclear in the boundary of the exposure pattern when the exposure pattern length is L1 than when the exposure pattern length is L2. That is, the diagram indicates that in the case of image deletion, the shorter the toner image length is, the more unclear the boundary of the luminance value is. It is therefore concluded that the shorter the toner image length is, the more blurred the toner image looks.
As explained with reference to
An exposure pattern controlled based on the result of the detection by the detecting section 50 will be described with reference to
As explained with reference to
A middle part of
It is indicated that the percentage of the thin line density relative to the thick line density is smaller than the threshold value in a site M1, a site M2, and a site M3 in the toner image detected. Accordingly, the detecting section 50 determines that image deletion has occurred in the sites M1, M2, and M3, and sends the result of the detection to the control section 80.
A bottom part of
The control section 80 adjusts the length of each pattern of the exposure by the exposure device 40 based on the degree of the image deletion. Preferably, the amount of toner to supply to each photosensitive roller 11 is increased for a higher degree of image deletion. Accordingly, the length of the pattern of the exposure by the exposure device 40 is increased so that the amount of toner to be supplied is increased in the case of a higher degree of image deletion. On the contrary, the length of the pattern of the exposure by the exposure device 40 is decreased so that the amount of toner to be supplied is decreased in the case of a lower degree of image deletion. As a result, an appropriate amount of toner is supplied according to the degree of the image deletion.
The percentage of the thin line density relative to the thick line density in the site M1 shown in the middle part of
The control section 80 adjusts the duration of the cleaning of the photosensitive rollers 11 by the cleaning sections 30 according to the degree of the image deletion detected by the detecting section 50. Specifically, the duration of the cleaning is made shorter when the percentage of the thin line density relative to the thick line density is larger, and the duration of the cleaning is made longer when the percentage of the thin line density relative to the thick line density is smaller. That is, the control section 80 makes the duration of the cleaning by the cleaning section 30 shorter for a larger percentage of the density of a toner image corresponding to the thin line 70b relative to the density of a toner image corresponding to the thick line 70a. As a result, the refreshing can be performed for an appropriate duration according to the degree of the image deletion.
According to the present embodiment, as described with reference to
In the present embodiment, the detecting section 50 detects image deletion based on the percentage of the thin line density relative to the thick line density. It is noted that the detecting section 50 is a sensor having a linear shape extending in the width direction of the intermediate transfer belt 15 (main scanning direction). The exposure pattern for detecting image deletion also extends in the width direction of the intermediate transfer belt 15. The detecting section 50 can therefore detect a region having a higher toner density and a region having a lower toner density of one toner image in terms of the width direction. The detecting section 50 can therefore detect image deletion only with a thick line or only with a thin line.
An image forming apparatus 100 according to the second embodiment of the present disclosure will be described with reference to
The image forming apparatus 100 includes a main body 200 and an image reading section 300. The image reading section 300 is disposed on the top surface of the main body 200. The image reading section 300 optically reads an original document to be copied and generates image data.
The main body 200 accommodates the photosensitive member refreshing device 1, a sheet feed cassette 210, a conveyance section 500, and a fixing section 600. The photosensitive member refreshing device 1 functions as an image forming section. The sheet feed cassette 210 is disposed in a lower part of the main body 200 and stores therein a sheet P to be conveyed to the image forming section. The conveyance section 500 is a path which extends from the sheet feed cassette 210 or a manual sheet feed tray 400 to an ejection roller pair 217 via the image forming section and the fixing section 600, and through which the sheet P is conveyed. The fixing section 600 fixes a toner image on the sheet P.
The image forming section transfers toner images of four colors to the intermediate transfer belt 15. The image forming section includes an image forming unit 5 and a toner replenishing section 7. The image forming unit 5 includes an image forming unit 5Y that forms a yellow toner image, an image forming unit 5M that forms a magenta toner image, an image forming unit 5C that forms a cyan toner image, and an image forming unit 5K that forms a black toner image.
The image forming unit 5Y includes the photosensitive roller 11, the primary transfer roller 12, the developing device 20, the cleaning section 30, the exposure device 40, and the charger 60. The image forming units 5M, 5C, and 5K have the same configuration as the image forming unit 5Y. The intermediate transfer belt 15 of the image bearing member 10 is wound around a drive roller 16 and a driven roller 19.
The toner replenishing section 7 includes a toner container 7Y that stores therein a yellow toner, a toner container 7M that stores therein a magenta toner, a toner container 7C that stores therein a cyan toner, and a toner container 7K that stores therein a black toner. The toners of the respective colors stored in the toner containers 7Y, 7M, 7C, and 7K are supplied to the developing devices 20 for the respective colors in the image forming units 5Y, 5M, 5C, and 5K.
The sheet feed cassette 210 accommodates the sheet P. The sheet P is plain paper, recycled paper, thin paper, thick paper, an overhead projector (OHP) sheet, for example. The manual sheet feed tray 400 is disposed on the outside of the right side of the main body 200. The sheet P is loaded on the manual sheet feed tray 400. The sheet P is conveyed from the sheet feed cassette 210 or the manual sheet feed tray 400 to the conveyance section 500.
The fixing section 600 includes a heating roller 601, a fixing roller 603, a pressure roller 605, a fixing belt 607, and an induction heating unit 609. The pressure roller 605 is in pressed contact with the fixing roller 603 to form a fixing nip part. The heating roller 601 and the fixing belt 607 are induction-heated by the induction heating unit 609. The heat of the heating roller 601 and the heat of the fixing belt 607 is applied to the fixing nip part. The sheet P bearing the toner images is conveyed to the fixing section 600. The sheet P passes through the fixing nip part, and thus the toner images are fixed onto the sheet P. The ejection roller pair 217 ejects the sheet P onto an exit tray.
The control section 80 initiates the refreshing before the sheet P is conveyed from the sheet feed cassette 210 or the manual sheet feed tray 400 to the conveyance section 500. In response to the initiation of the refreshing, the detecting section 50 detects the toner images formed on the intermediate transfer belt 15.
So far, the embodiments of the present disclosure have been described with reference to the drawings (
(1) One detecting section 50 is disposed above the intermediate transfer belt 15 according to the description made with reference to
(2) The photosensitive member refreshing device 1 includes four photosensitive rollers 11 according to the description made with reference to
(3) The detecting section 50 is disposed above and opposed to the intermediate transfer belt 15 according to the description made with reference to
(4) The toner images on the image bearing member 10 are formed using the toners of the four colors, and the toner images of the four colors are each formed from one thick line and three thin lines according to the description made with reference to
(5) The three thin lines forming each toner image on the image bearing member 10 have the same length according to the description made with reference to
(6) The toner images on the image bearing member 10 are formed using the toners of the four colors, and the toner images are formed based on the same pattern according to the description made with reference to
(7) The developing devices 20 use the same color for a thick line pattern and thin line patterns to form a toner image, and the toner density for the thick line pattern and the toner density for the thin line patterns are detected by the detecting section 50 according to the description made with reference to
(8) The photosensitive member refreshing device 1 supplies an appropriate amount of toner to each photosensitive roller 11 based on the result of the detection by the detecting section 50 to perform the refreshing according to the description made with reference to
Number | Date | Country | Kind |
---|---|---|---|
2014-030694 | Feb 2014 | JP | national |