JP2020201406A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can uniformly charge a long photoreceptor, and can apply charging rollers with various different shapes including individual differences.SOLUTION: An image forming apparatus 1 comprises: photoreceptors 11; charging units 20 that each have charging rollers 40 that are in contact with a photoreceptor surface 11a moved by a rotational movement centered on the rotational axis of the photoreceptor 11 and thereby to charge the photoreceptor surface 11a; and exposure units 50 that each expose the photoreceptor 11 charged by the charging unit 20 to form an electrostatic latent image. The charging units 20 each have the charging rollers 40 that are provided in plurality along a direction intersecting with the direction of movement of the photoreceptor surface 11a such that the ends of charging areas adjacent to each other overlap in the direction of movement of the photoreceptor surface 11a; the exposure units 50 increases the amount of exposure of the photoreceptor surface 11a charged by the overlapping portion of the plurality of charging rollers 40 compared with the amount of exposure of the photoreceptor surface 11a charged by a non-overlapping portion of the plurality of charging rollers 40.SELECTED DRAWING: Figure 1

Description

The present invention relates to an image forming apparatus having a charging roller that charges the surface of the photoconductor by contacting the surface of the photoconductor.

The image forming apparatus needs to charge the surface of the photoconductor in advance in order to form an electrostatic latent image on the surface of the photoconductor.
Conventionally, such an image forming apparatus has a corona charging method in which the surface of a photoconductor is charged by a corona discharger incorporated in the apparatus.
Such a corona charging type image forming apparatus has many problems such as the need for a high voltage power supply for supplying power to the corona discharger and the generation of harmful ozone by the discharge.

Therefore, in order to solve the problem of the corona charging method, a contact charging type image forming apparatus for charging the photoconductor by bringing the charging roller into contact with the photoconductor with a uniform contact pressure has been used.

A large-format image forming apparatus using such a contact charging method requires a long charging roller.
However, it is difficult for a long charging roller to come into contact with a uniform contact pressure over the entire length in the width direction of the photoconductor due to problems such as deflection or difficulty in processing.
For this reason, it is difficult for a contact electrification type image forming apparatus using a long charging roller to contact a photoconductor with a uniform contact pressure to uniformly charge the image, and as a result, it is practically used. It was not something that could be offered.

Therefore, for example, Patent Document 1 describes a charging device provided with a plurality of charging rollers facing the photoconductor in an axial direction orthogonal to the rotation direction of the photoconductor.
Since the charging device described in Patent Document 1 includes a plurality of charging rollers in a direction orthogonal to the rotation direction of the photoconductor, the photoconductor is provided with a plurality of charging rollers that are significantly shorter than the width of the photoconductor. It can cover the entire width direction.
Therefore, the charging device described in Patent Document 1 can solve the problems of bending of the charging roller and workability.

However, in the charging device described in Patent Document 1, as shown in FIG. 19, the charging potential of the photoconductor 200 of the overlapping portion W of the adjacent charging roller 100 is higher than the charging potential of the non-overlapping portion, for example. When the charging potential of the photoconductor surface 210 of the non-overlapping portion of the charging roller 100 is −500V, the charging potential of the photoconductor surface 210 of the overlapping portion W of the charging roller is −550V.
As described above, when the charging potential of the photoconductor surface 210 of the overlapping portion W of the charging roller 100 becomes larger than the charging potential of the photoconductor surface 210 of the non-overlapping portion of the charging roller 100, printing is performed as shown in FIG. There is a problem that a density difference occurs in the density and the halftone image density of the overlapping portion W is expressed lightly.
In the graph in FIG. 19, the vertical axis (Y) shows the surface potential of the photoconductor 200 with the negative charging direction facing upward, and the horizontal axis (X) shows the axial position of the photoconductor.
Further, in the graph in FIG. 19, the solid line A shows the primary charge position (dark part potential), the broken line B shows the halftone potential, and the alternate long and short dash line C shows the bright part potential.

Therefore, in Patent Document 2, the outer diameter of the end portion that is the overlapping portion of the charging region of the adjacent contact charging member (charging roller) is set smaller than the outer diameter of the central portion in the axial direction. An image forming apparatus capable of obtaining good image quality even in a portion where adjacent contact charging members (charging rollers) overlap is described.

However, in the image forming apparatus described in Patent Document 2, the outer diameter of the end portion where the charging roller is an overlapping portion of the charging region of the adjacent contact charging member (charging roller) is set to the outer diameter of the central portion in the axial direction. There are problems that the shape is limited to a shape that is set smaller than that, that is, a so-called crown shape, and that individual differences cannot be dealt with.
Considering that various shapes of charging rollers have been proposed in order to solve the problem of the contact charging method, it is a big problem that the charging rollers are limited to the crown shape.

Therefore, the applicants of the present patent have described in Patent Document 3 that a plurality of charging rollers provided in the charging portion overlap the photoconductor surface so that the ends of adjacent charging regions overlap in the moving direction of the photoconductor surface. Of the plurality of charging rollers, at least one charging roller is provided at an inclination angle with respect to a direction orthogonal to the movement direction of the surface of the photoconductor in the rotation axis direction. We are proposing an image forming device.
In the image forming apparatus described in Patent Document 3, the tilt angle corresponding to the charging rollers having different shapes and different shapes is set including individual differences, so that the surface of the photoconductor including the overlapping portion of the charging region of the charging rollers The charged region can be uniformly charged.

Japanese Unexamined Patent Publication No. 8-305128 JP-A-2007-178460 Japanese Patent Application No. 2019-6703

However, even if the function-separated roller described in Patent Document 3 is applied to the charging roller, the voltage drop carried by the electric resistance component of the charging roller cannot be ignored, and the photoconductor is charged for the first time. A step is likely to occur between the potential and the charging potential thereafter, and the charging potential on the surface of the photoconductor in the overlapping portion of the charging region of the charging roller is also likely to be stepped.
Therefore, even if the tilt angle of the charging roller is adjusted as in the image forming apparatus described in Patent Document 3, the charged region on the surface of the photoconductor including the overlapping portion of the charged region of the charging roller can be uniformly charged. There are things you can't do.

The present invention has been made in view of the above, and it is possible to uniformly charge a long photoconductor, that is, it is possible to obtain a uniform image having no difference in image density, and various kinds of images can be obtained. It is an object of the present invention to provide an image forming apparatus capable of applying charging rollers having different shapes including individual differences.

In order to solve the above-mentioned problems and achieve the object, the image forming apparatus according to the present invention comes into contact with the photoconductor and the surface of the photoconductor that is moved by a rotational movement about the rotation axis of the photoconductor. In an image forming apparatus including a charging unit having a charging roller for charging the surface of the photoconductor and an exposure unit that exposes the photoconductor charged by the charging unit to form an electrostatic latent image. A plurality of charging portions are provided along the direction in which the charging rollers intersect with each other in the moving direction of the photoconductor surface so that the ends of adjacent charged regions overlap in the moving direction of the photoconductor surface. The exposure unit increases the exposure amount of the photoconductor surface charged by the overlapping portions of the plurality of charging rollers to be larger than the exposure amount of the photoconductor surface charged by the non-overlapping portions of the plurality of charging rollers. It is characterized by having done it.

Further, in the image forming apparatus according to the present invention, in the above invention, the exposed portion uses a plurality of LEDs arranged side by side in parallel with the axis of the photoconductor as a light source, and the image forming apparatus uses the plurality of LEDs. By controlling the lighting and extinguishing of the light source, the charging potential of the photoconductor surface corresponding to the region where the plurality of charging rollers overlap and the charging potential of the photoconductor surface corresponding to the region where the plurality of charging rollers do not overlap. It is characterized by having a charging potential difference adjusting unit that controls the amount of exposure by the exposed unit so as to reduce the difference between the two.

Further, in the image forming apparatus according to the present invention, in the above invention, the plurality of charging rollers are inclined with respect to a direction in which one or more of the charging rollers are orthogonal to the movement direction of the surface of the photoconductor. It is characterized in that it is provided at an angle.

Further, the image forming apparatus according to the present invention is characterized in that, in the above invention, the plurality of charging rollers are provided so that the tilt angle can be adjusted within a predetermined range.

Further, in the image forming apparatus according to the present invention, in the above invention, the charging potential difference adjusting unit charges the plurality of charging intensity of the LED for each pixel of the electrostatic latent image formed on the surface of the photoconductor. The LED related to the charging potential of the photoconductor surface corresponding to the region where the rollers overlap is made larger than the LED related to the charging potential of the photoconductor surface corresponding to the region where the plurality of charging rollers do not overlap. As described above, it is characterized in that the lighting and extinguishing of the plurality of LEDs are controlled.

Further, in the image forming apparatus according to the present invention, in the above invention, the exposed portion has a plurality of LED heads in which a plurality of the LEDs are arranged in a straight line, and the photoconductor is formed by the plurality of LED heads. It is characterized by covering the exposure range in the axial direction of.

Further, the image forming apparatus according to the present invention further includes a surface potential detecting unit for detecting the potential on the surface of the photoconductor in the above invention, and the plurality of the image forming apparatus is based on the potential detected by the surface potential detecting unit. Exposure by the exposed portion so as to reduce the difference between the charging potential of the photoconductor surface corresponding to the region where the charging rollers overlap and the charging potential of the photoconductor surface corresponding to the region where the plurality of charging rollers do not overlap. It is characterized by controlling the amount.

The image forming apparatus according to the present invention charges the surfaces of the photoconductor by contacting the surface of the photoconductor that is moved by the rotational movement about the rotation axis of the photoconductor, so that the edges of adjacent charged regions are charged. Since a plurality of charging rollers are provided along the directions intersecting the moving directions of the photoconductor surface so that the portions overlap in the moving direction of the photoconductor surface, the plurality of charging rollers provide the shaft of the photoconductor. The charged region can be covered in the direction.
Further, in the image forming apparatus according to the present invention, the exposure unit is exposed to the exposure amount of the surface of the photoconductor charged by the overlapping portions of the plurality of charging rollers and the exposure amount charged by the non-overlapping portions of the plurality of charging rollers. Since the exposure amount is larger than the exposure amount of the body surface, the charging potential of the photoconductor surface corresponding to the region where the plurality of charging rollers overlap and the photoconductor surface corresponding to the region where the plurality of charging rollers do not overlap. The difference from the charging potential of is small.
Therefore, the image forming apparatus according to the present invention can uniformly charge a long photoconductor, that is, can obtain a uniform image without a step in image density, and has different shapes. The charging roller can be applied including individual differences.

FIG. 1 is a diagram schematically showing an overall structure including a control unit of the image forming apparatus according to the first embodiment of the present invention. FIG. 2 is an enlarged view of the periphery of the photoconductor of the image forming apparatus shown in FIG. FIG. 3 is a diagram for explaining the positional relationship between the photoconductor and the three charging rollers, and is also a diagram showing the cleaning roller. FIG. 4 is a diagram for explaining the detailed configuration of the exposed portion and the positional relationship between the exposed portion, the three charging rollers, and the photoconductor. 5A and 5B are perspective views of an assembly in which bearings of three charging rollers are attached to a fixed frame, and FIG. 5B is a photosensitive member with respect to the assembly shown in FIG. 5A. It is a figure which arranged. FIG. 6 is a diagram showing a charging roller and a cleaning roller. 7A is a view of the assembly shown in FIG. 5 as viewed from the back surface side with respect to the bearing fixing surface of the fixing frame, and FIGS. 7B and 7C are screws for fixing the bearing portion. It is an enlarged view around the part to be bearing. FIG. 8 is a view of the periphery of the bearing portion attached to the fixed frame as viewed from the axial direction, and is a partial cross-sectional view. FIG. 9 is a view of the periphery of the bearing portion attached to the fixed frame as viewed from a direction orthogonal to the axial direction, and is a partial cross-sectional view. FIG. 10 is a diagram for explaining a cross amount and an inclination angle of the charging roller. FIG. 11 is a diagram for explaining that one pixel of the electrostatic latent image is configured based on the number of times the LED is lit (the number of lines) in the sub-scanning direction. FIG. 12 is a diagram for explaining that the charged region on the surface of the photoconductor including the overlapping portion of the charged region of the charging roller is uniformly charged by turning on and off the plurality of LEDs by the charging potential difference adjusting unit. .. FIG. 13 is a diagram for explaining that the density difference is eliminated and the print density becomes uniform by controlling the lighting and extinguishing of the plurality of LEDs by the charging potential difference adjusting unit. FIG. 14 is a diagram schematically showing an overall structure including a control unit of the image forming apparatus according to the second embodiment of the present invention. FIG. 15 is an enlarged view of the periphery of the photoconductor of the image forming apparatus shown in FIG. FIG. 16 is a diagram for explaining the positional relationship between the exposed portion, the three charging rollers, the photoconductor, and the surface potential detecting portion. FIG. 17 is a diagram for explaining a modification of the shape of the charging roller. FIG. 18 is a diagram for explaining a modified example of the arrangement of the charging rollers. FIG. 19 is a diagram for explaining a problem of the prior art. FIG. 20 is a diagram for explaining a problem of the prior art.

Hereinafter, preferred embodiments of the image forming apparatus according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram schematically showing an overall structure including a control unit of the image forming apparatus 1 according to the first embodiment of the present invention. FIG. 2 is an enlarged view of the periphery of the photoconductor 11 of the image forming apparatus 1 shown in FIG. FIG. 3 is a diagram for explaining the positional relationship between the photoconductor 11 and the three charging rollers 40, and is also a diagram showing the cleaning roller 17. FIG. 4 is a diagram for explaining the detailed configuration of the exposure unit 50 and the positional relationship between the exposure unit 50, the three charging rollers 40, and the photoconductor 11. 5A and 5B are perspective views of an assembly in which each bearing portion 21 of the three charging rollers 40 is attached to the fixed frame 30, and FIG. 5B is a perspective view of the assembly shown in FIG. 5A. It is a figure which arranged the photoconductor 11. FIG. 6 is a diagram showing a charging roller 40 and a cleaning roller 17. 7 (a) is a view of the assembly shown in FIG. 5 as viewed from the back surface side with respect to the bearing fixing surface 32a of the fixed frame 30, and (b) and (c) are views of the bearing portion 21. It is an enlarged view around the part to be fixed by a screw. FIG. 8 is a view of the periphery of the bearing portion 21 attached to the fixed frame 30 as viewed from the axial direction, and is a partial cross-sectional view. FIG. 9 is a view of the periphery of the bearing portion 21 attached to the fixed frame 30 as viewed from a direction orthogonal to the axial direction, and is a partial cross-sectional view. FIG. 10 is a diagram for explaining a cross amount T and an inclination angle A of the charging roller 40. FIG. 11 is a diagram for explaining that one pixel of the electrostatic latent image is configured based on the number of times the LED 51a is lit (the number of lines) in the sub-scanning direction SSD. FIG. 12 is a diagram for explaining that the charged region on the surface of the photoconductor including the overlapping portion of the charged region of the charging roller 40 is uniformly charged by turning on and off the plurality of LEDs 51a by the charging potential difference adjusting unit 71. Is. FIG. 13 is a diagram for explaining that the density difference is eliminated and the print density becomes uniform by controlling the lighting and extinguishing of the plurality of LEDs 51a by the charging potential difference adjusting unit 71.
The image forming apparatus 1 according to the first embodiment of the present invention is a tandem type in which a plurality of photoconductors 11 are arranged according to the color of the toner, and moves by rotating the photoconductor 11 and a rotation axis. It has a contact charging type charging unit 20 including a charging roller 40 that charges the photoconductor surface 11a by contacting the photoconductor surface 11a.

Hereinafter, the overall configuration of the image forming apparatus 1 will be described.
The image forming apparatus 1 transfers the toner image to a transfer material P such as paper and four color-coded units 10 corresponding to the toner colors of the four primary colors of cyan C, magenta M, yellow Y, and black K. A transfer unit 14 for printing, a transport unit 15 for transporting the transfer material P, a fixing unit 16 for fixing the toner image transferred to the transfer material P, an input unit 60 for inputting various information related to printing, and various information related to printing. It has a storage unit 61 for storing and a control unit 70 for controlling the operation of each unit of the image forming apparatus 1.

First, the color-coded unit 10 will be described.
Since all of the four color-coded units 10 have substantially the same configuration except that the toner colors are different, individual description thereof will be omitted.

The color-coded unit 10 is an exposure unit that forms an electrostatic latent image by exposing the photoconductor 11, a charging unit 20 that charges the surface of the photoconductor 11, and a photoconductor surface 11a that is charged by the charging unit 20. It has 50, a developing unit 12 that develops a toner on an electrostatic latent image formed on the photoconductor 11 to make it a visible image, and a photoconductor cleaner 13 that cleans unnecessary residual toner.

The photoconductor 11 has a drum shape, and in this embodiment, the outer diameter is set to 80 mm.
Further, in the first embodiment, the photoconductor 11 is controlled by the control unit 70 with a surface potential of −500 V as a target.
For example, when the discharge start voltage of the charging roller 40 is -600V, when -1100V, which is obtained by adding -500V, which is the target surface potential of the photoconductor 11, to the discharge starting voltage of -600V, is applied to the charging roller 40, the light is photosensitive. The surface potential of the body 11 becomes −500 V.

The charging unit 20 is a feature portion of the present invention, and is a three charging roller 40 that charges the photoconductor surface 11a by coming into contact with the photoconductor surface 11a that is moved by a rotational movement about the rotation axis of the photoconductor. Further, it has three cleaning rollers 17 provided corresponding to each charging roller 40 so as to remove toner or foreign matter adhering to each charging roller 40.

As shown in FIG. 3, the charging rollers 40 intersect in the moving direction of the photoconductor surface 11a so that the ends of adjacent charged regions 42 (elastic contact portions) overlap in the moving direction of the photoconductor surface 11a. Three are provided along the direction.
In the first embodiment, the charging unit 20 has an inclination angle A with respect to a direction in which two of the three charging rollers 40 are orthogonal to the movement direction of the photoconductor surface 11a in the rotation axis direction. It is provided.
More specifically, one central charging roller 40 is provided with the rotation axis direction oriented orthogonal to the moving direction of the photoconductor surface 11a, and two charging rollers 40 on both sides rotate the photoconductor surface in the rotation axis direction. The inclination angle A is provided with respect to the direction orthogonal to the moving direction of 11a.

Each charging roller 40 applies a straight shape in which the outer diameter dimension of the elastic contact portion 42, which will be described later, is constant in the axial direction.
The charging roller 40 may have a so-called crown shape in which the central portion of the elastic contact portion 42 is convex, or an inverted crown shape in which the central portion of the elastic contact portion 42 is concave. It is preferable that the outer diameter deviation of the portion is 0.2 mm or less.

The charging roller 40 is a portion that is elastically contacted with the metal shaft portion 41 and is also a charging region, and is formed from the conductive elastic body layer and the conductive elastic body layer. A function-separated roller covered with an oil oozing prevention layer, a resistance adjusting layer, and a surface protective layer in this order is applied (see, for example, Japanese Patent Application Laid-Open No. 2-3118868).
The charging roller 40 is a single-layer roller in which the metal shaft portion 41 is simply covered with a semi-conductive rubber, or a two-layer roller in which a surface protection layer is simply added to the semi-conductive rubber layer. The voltage drop carried by the resistance component cannot be ignored, and a step is likely to occur between the charging potentials of the first rotation of the photoconductor 11 and the subsequent charging potentials, and the charging of the photoconductor 11 in the overlapping portion W of the adjacent charging rollers 40 Since a step is likely to occur in the potential, it is preferable to apply a function-separated roller.
In order to reduce the voltage drop carried on the electric resistance component of the charging roller 40 as much as possible, it is not enough to simply reduce the electric resistance. In order to avoid the occurrence of pinholes due to insufficient withstand voltage of the photoconductor 11, the volume resistivity of the resistance adjusting layer that substantially controls the electrical resistance component of the charging roller 40 is about 1 × 10 7 [Ω · cm]. It is preferable to make the layer as thin as possible within the range where the thickness does not cause a resistivity failure.

Here, a more specific configuration example of the charging roller 40 will be described.
In the first embodiment, the outer diameter of the elastic contact portion 42 is 12 mm and the length is 322 mm.
Metal shaft 41: diameter 8 mm,
Conductive elastic layer: A thickness of approximately 2 mm, ethylene, propylene, diene rubber (EPDM), SBR, NR, etc. mixed with an electronic conductive agent such as carbon black, and having a volume resistivity of 1 × 10 cubed. It has a low hardness of 30 degrees (Hs: JIS A) at [Ω · cm] or less.
Oil exudation prevention layer from the conductive elastic body layer ・ ・ ・ Thickness 10 μm
Resistance adjustment layer: An ionic conduction layer that enhances withstand voltage (leakage resistance), and has a minimum thickness of 50 μm or more that satisfies the dielectric breakdown voltage.
The amount of electronic conductive agent such as carbon black contained in the resistance adjusting layer is 10% by volume or less with respect to rubber.
As a specific example, perchlorate (quaternary ammonium) as an ionic conductive agent is applied to epichlorohydrin-ethylene oxide copolymer rubber (CHC), hydrogenated nitrile rubber, etc., which are polymer compounds having a thickness of 160 μm and an ether bond. Salt), an antistatic agent, etc. are blended to obtain a volume resistivity of 1 × 10 to the 7th power [Ω · cm].
Surface protective layer: A thickness of 10 μm, a fluororesin (vinylidene fluoride-ethylene tetrafluoroethylene copolymer resin) mixed with electron conductive particles (magnetite or titanium black), and a volume resistivity of 10 to the 7th power 10 to the 10th power and shore hardness (D type) of 65 degrees or less.
In the surface protective layer, convex portions caused by the rough surface forming particles are distributed and formed, and the outer diameter of the rough surface forming particles is 13 μm and the thickness other than the convex portions is 10 μm (Japanese Patent Laid-Open No. 2007-178559). , JP-A-2007-264491).
By applying such a surface protective layer, the contact area between the photoconductor 11 and the charging roller 40 can be reduced, and a constant discharge region can be secured in the gap, thereby improving the charging performance. Therefore, it is possible to take into consideration the DC voltage method, which is advantageous for cost reduction, and it is also possible to reduce the vibration noise that tends to be generated in the AC voltage method.

Further, in order to maintain the effect of each of the above layers even at the end portion of the elastic contact portion 42, C chamfering is performed at the end portion. More specifically, the deformation of the conductive elastic body layer due to the contact pressure of the charging roller 40 causes the discharge resistance at the end of the elastic contact portion 42 to be locally reduced, so that the photoconductor 11 corresponding to the end portion The charging potential is larger than that of other parts, and as a result, white streaks are prevented from occurring in the sub-scanning direction SSD of the obtained print output image.

Since the charging roller 40 is in contact with the photoconductor 11, if it is used for a long period of time, problems such as deterioration of charging performance and uneven charging will occur due to the adhesion of toner and foreign matter adhering to the photoconductor surface 11a.
In order to solve such a problem, in the first embodiment, for example, the cleaning roller 17 disclosed in Japanese Patent Application Laid-Open No. 8-137208 is applied as the cleaning roller 17.
The cleaning roller 17 can solve the problems such as deterioration of charging performance and uneven charging.

As shown in FIG. 6, the cleaning roller 17 has a metal shaft portion 17a and a cleaning material 17b spirally wound around the metal shaft portion 17a, and is driven while being in contact with the charging roller 40. It is designed to be rotated.

The cleaning material 17b is a band-shaped member made of polyurethane foam or the like, and is clogged with a convex portion having the cleaning material 17b and a concave portion between which the shaft portion is exposed by being spirally wound around the metal shaft portion 17a. Can be prevented.
As disclosed in Japanese Patent Application Laid-Open No. 2012-103641, the cleaning material 17b may have a width of 5 mm to 24 mm and a thickness of 1.9 mm to 3.6 mm along the metal shaft portion 17a.

Further, the charging portion 20 has a bearing portion 21 of the metal shaft portion 41 of the three charging rollers 40 and a fixed frame 30 to which each bearing portion 21 of the three charging rollers 40 is fixed.

A pair of bearing portions 21 are provided so as to pivotally support both end portions of each charging roller 40, and as shown in FIGS. 8 and 9, a fixed portion 22 which is a portion fixed to the fixed frame 30 A movable bearing portion 23 in which a charging roller 40 is attached to the fixed portion 22 so as to be pressurized in the direction of the photoconductor 11 is provided.

The fixed portion 22 is made of an insulating material, and the spring accommodating portion 22a in which a spring S for pressurizing the elastic contact portion 42 of the charging roller 40 against the photoconductor 11 by urging the movable bearing portion 23 is housed. And a guide wall portion 22b that guides the movable bearing portion 23 in the urging direction.

The movable bearing portion 23 includes an electrode holding portion 24 in which an electrode plate E for applying a voltage to the charging roller 40 is held, and a shaft end rotation support in which the metal shaft portion 41 of the charging roller 40 is rotatably supported. It has a part 26 and.

The electrode holding portion 24 is made of an insulating material, and holds the axial urging member 25a that holds the electrode plate E and the axial urging member 25a that urges the end surface of the metal shaft portion 41 in the axial direction. Is formed so as to be connected to the shaft end rotation support portion 26 along the axial direction of the metal shaft portion 41.

The axial urging member holding portion 25 urges the conductive axial urging member 25a connected to the electrode plate E with a metal spring S axially at the end surface of the metal shaft portion 41 of the charging roller 40. It is held so that it can be used.

The shaft end rotation support portion 26 is made of a conductive resin material, and in particular, a material having good slidability is applied in consideration of the rotation direction of the metal shaft portion 41 and the slipperiness in the axial direction. There is.
The shaft end rotation support portion 26 is formed with a metal shaft portion holding recess 27 formed so as to be connected to the electrode holding portion 24 along the axial direction of the metal shaft portion 41.
The inner diameter of the metal shaft portion holding recess 27 is set to be slightly larger than the outer diameter of the metal shaft portion 41.
Further, the metal shaft portion holding recess 27 is set so that the depth in the axial direction allows the metal shaft portion 41 to slide in the axial direction while receiving the urging force of the axial urging member 25a.

An appropriate urging force acts not only in the direction of contact with the photoconductor 11 but also in the axial direction of the metal shaft portion 41 on the charging roller 40 pivotally supported at both ends of the metal shaft portion 41 by such a bearing portion 21. It is supposed to be done.
Therefore, even if the charging roller 40 is provided with an inclination angle A with respect to a direction in which the rotation axis direction is orthogonal to the moving direction of the photoconductor surface 11a, the charging roller 40 rotates stably while being in pressure contact with the photoconductor 11. You can do it.

The electrode plates E may be provided on both of the pair of bearing portions 21, or may be provided only on one of the bearing portions 21.

Further, in the first embodiment, the bearing portion 21 of the cleaning roller 17 is rotatably supported in the same manner as the charging roller 40.
That is, the movable bearing portion 23 holds the electrode plate E at a position where the electrode holding portion 24 corresponds to the cleaning roller 17.
Further, the shaft end rotation support portion 26 is formed with a metal shaft portion holding recess 28 corresponding to the cleaning roller so as to line up with the metal shaft portion holding recess 27 corresponding to the charging roller 40.
The depth of the metal shaft portion holding recess 28 is set so that the metal shaft portion 17a of the cleaning roller 17 can slide in the axial direction while receiving the urging force of the axial urging member 25b.

The fixed frame 30 is fixed to a housing (not shown) or a frame (not shown) of the image forming apparatus 1 so as to extend along the width direction of the photoconductor 11.
As shown in FIG. 7, the fixed frame 30 is arranged so as to extend along the width direction of the photoconductor 11 with the housing of the image forming apparatus 1 or the fixed portion 31 fixed to the frame. It has a plurality of charging roller arranging portions 32 on which a bearing fixing surface 32a to which each bearing portion 21 of the three charging rollers 40 is fixed is formed.

When the plurality of charging roller arranging portions 32 are fixed to the bearing fixing surface 32a by the plurality of screw fixing portions 33 of each bearing portion 21 corresponding to the three charging rollers 40 and each bearing portion 21 by the screw fixing portion 33. A plurality of angle adjusting guide slits 34 are formed to serve as guide portions for fixing the charging roller 40 with an inclination angle A with respect to a direction orthogonal to the moving direction of the photoconductor surface 11a. ..

Two screw fixing portions 33 are provided corresponding to each bearing portion 21. More specifically, the screw fixing portion 33 is a screw insertion hole provided at two locations in the fixed portion 22 of each bearing portion 21 corresponding to a screw hole (not shown).

The angle adjusting guide slit 34 is an elongated hole formed in the bearing fixing surface 32a, and is provided at one place corresponding to each bearing portion 21.
More specifically, the angle adjusting guide slit 34 is a slide guide of the guide protrusions 22c formed at one position on the fixed portion 22 of each bearing portion 21.

In the first embodiment, the three charging rollers 40 are set so that the cross amount T with the photoconductor 11 is 0.1 mm at the center of the charging roller 40 in the specific configuration described above. The photoconductor 11 is driven to rotate.
Here, the cross amount T is a value calculated by [cross amount T = radius R1 of the photoconductor + radius R2-distance between the photoconductor and the axis center of the charging roller] (see FIG. 10).

Further, the charging rollers 40 are arranged along a direction intersecting the moving direction of the photoconductor surface 11a so that the ends of the elastic contact portions 42 as adjacent charged regions of each other overlap in the moving direction of the photoconductor surface 11a. Each charging roller 40 is set so that the inclination angle A can be adjusted within a range of 0.2 degrees or more and 2 degrees or less with respect to a direction orthogonal to the moving direction of the photoconductor surface 11a.
In such an adjustment range of the inclination angle A, when each of the charging rollers 40 is set to the above-mentioned dimensions, the difference B in the axial center position at both end positions of the elastic contact portion 42 of the charging roller 40 (see FIG. 10). The inclination angle A is adjusted in the range of 1.1 mm or more and 11.2 mm or less.

The reason why the inclination angle A is set in the range of 0.2 degrees or more and 2 degrees or less is based on the result of the experiment carried out by the patent applicants.
That is, when the inclination angle A is less than 0.2 degrees, the charging potential of the photoconductor 11 in the overlapping portion of the two adjacent charging rollers is higher than the charging potential of the photoconductor 11 in the non-overlapping portion. As a result, the halftone image density of the photoconductor 11 in the portion where the charging rollers 40 overlap is expressed lightly.
On the other hand, when the inclination angle A exceeds 2 degrees, the deviation of the pressure distribution to the photoconductor 11 becomes too large, the correct charge distribution cannot be obtained, and image unevenness occurs.

The charging unit 20 having such a configuration can easily adjust the inclination angle A within a predetermined range (in this embodiment, a range of 0.2 degrees or more and 2 degrees or less).
That is, the charging portion 20 fits the guide protrusions 22c formed at each of the fixed portions 22 of the pair of bearing portions 21 into the corresponding angle adjustment guide slits 34 of the fixing frame 30, and then fits each angle adjustment guide. Each guide protrusion 22c is moved in the slit 34 to adjust the inclination angle A within a predetermined range, and then the fixed portion 22 is screwed and fixed to the fixing frame 30.

By the way, in the present patent applicants, the image forming apparatus using the crown-shaped charging roller described in Patent Document 2 (Japanese Unexamined Patent Publication No. 2007-178460) described above initially has overlapping charging rollers. Although it is possible to reduce the concentration step in the part, it was confirmed by experiments that the concentration step occurs as the durability increases.
The patent applicants presume that this is due to the fact that the film thickness of the photoconductor is reduced due to durability and the space charge in the photoconductor layer is increased.
Further, the patent applicants have found that the degree of the concentration step in the overlapping portion W of the adjacent charging rollers 40 is not necessarily the same due to individual differences, contact pressure differences, dimensional errors, environmental differences, etc. of the photoconductor 11 and the charging rollers 40. It was also confirmed by experiment that it should not be done.

In the image forming apparatus 1 of this embodiment, since the charging unit 20 can adjust the inclination angle A, individual differences, contact pressure differences, dimensional errors, and environmental differences between the photoconductor 11 and the charging roller 40 Alternatively, by adjusting the inclination angle A according to the difference in durability, it is possible to stably reduce the concentration step in the overlapping portion W of the charging roller 40.

The exposed portion 50 is a feature portion of the present invention, and the exposure amount of the photoconductor surface 11a charged by the overlapping portion of the adjacent charging roller 40 is the exposure amount of the photoconductor surface charged by the non-overlapping portion of the adjacent charging roller 40. It is designed to be larger than the exposure amount of 11a.
In the first embodiment, the exposure unit 50 is realized by a known LED head 51 using a plurality of LEDs (Light Emitting Diodes) 51a arranged in parallel with the axis of the photoconductor 11 as a light source, and in the first embodiment. It has three LED heads 51 and covers the exposure range of the photoconductor 11 in the axial direction (hereinafter, referred to as the main scanning direction MSD).
Each LED head 51 includes a plurality of LEDs 51a arranged side by side in a straight line, and has a lens (not shown) that forms an image of the light of each LED 51a on the photoconductor surface 11a of the photoconductor 11.
Each LED 51a of the LED head 51 is controlled to be turned on and off by the control unit 70.

The LED head 51 has a plurality of pixels arranged in a matrix in a sub-scanning direction SSD orthogonal to the main scanning direction MSD and the main scanning direction MSD by blinking each LED 51a of the plurality of LEDs 51a arranged in the main scanning direction MSD. An electrostatic latent image composed of pxl) is formed on the photoconductor surface 11a of the photoconductor 11 rotating at a predetermined speed.

In the first embodiment, as shown in FIG. 11, the writing of the electrostatic latent image is composed of six lines for each dot. Specifically, the lighting of the LED 51a per dot is composed of six lines from the first line L1 to the sixth line L6. That is, for each dot, one dot of the electrostatic latent image to be drawn on the photoconductor surface 11a is drawn by six times of light emission of the LED 51a for writing, and the first to sixth lines L1 to L6 are used. The lighting intensity of the LED is controlled.
However, in the following description, when one dot of the electrostatic latent image is formed on the surface of the photoconductor 11a, the maximum number of times (number of lines) of the LED that lights for a predetermined time is 6 times (6 lines L1- The case of L6) will be described, but the number of times the LED is lit is not limited to six.
At this time, the third line L3 to the sixth line L6 as the first light emission are configured to control lighting (intensity) or extinguishing based on the latent image data.
For example, in normal printing, that is, printing based on latent image data, thin lines and the like tend to be printed lighter than other parts, so enhancement correction (γ) that makes the print density darker than the image data. The configuration is such that the third line L3 to the sixth line L6 are provided for writing the latent image data that has been corrected (well-known correction such as correction).

The lighting (intensity) or extinguishing is controlled in the same manner regardless of the overlapping portion W and the non-overlapping portion of the adjacent charging rollers 40.

Further, in the first embodiment, as the second light emission, the charging potential of the photoconductor 11 of the overlapping portion W of the adjacent charging roller 40 becomes higher in the negative direction than the charging potential of the non-overlapping portion, and as a result, The first line L1 and the second line L2 are provided for writing in order to correct the problem of the density step that the halftone image density of the overlapping portion is expressed lightly.
Specifically, regardless of the latent image data, the LED 51a (ranges W1 and W2 in FIG. 4) related to the charging potential of the photoconductor surface 11a corresponding to the overlapping portion of the adjacent charging rollers 40 is the first in the range W1. The photoconductor surface 11a corresponding to the region where the plurality of charging rollers 40 do not overlap is lit on the line L1 (the second line L2 is extinguished) and lit on the second line L2 in the range W2 (the first line L1 is extinguished). In the LED 51a (range other than the ranges W1 and W2 in FIG. 4) related to the charging potential, both the first line L1 and the second line L2 are turned off.

The portion of the photoconductor surface 11a charged with a negative charge by the three charging rollers 40 irradiated with the light of the LED 51a is statically eliminated according to its intensity, and becomes relatively positive compared to the potential of the developing roller 12b. As a result, negatively charged toner is attached.
The light energy (exposure amount) of the LED 51a that irradiates the photoconductor surface 11a can be expressed by "output watt x lighting time" of the LED head 51a, and the static elimination level of the photoconductor surface 11a by the LED head 51a is the LED head 51a. It depends on the magnitude of the light energy (exposure amount) of.
In the configuration of the prior art in which the first line L1 to the second line L2 are not provided, the charging potentials of the photoconductor 200 of the overlapping portion W of the adjacent charging rollers 100 as shown in FIG. 19 do not overlap. For example, when the charging potential of the photoconductor surface 210 of the non-overlapping portion of the charging roller 100 is −500 V, the charging potential of the photoconductor surface 210 of the overlapping portion W of the charging roller is −500V. It becomes 550V.
However, in the first embodiment, since the first line L1 to the second line L2 are provided, by adjusting the lighting time of the first line L1 to the second line L2, as shown in FIG. The charging potential -550V of the photoconductor surface 210 of the overlapping portion W of the charging roller can also be corrected (statically eliminated) to -500V, and the photoconductor surface 11a including the overlapping portion W of the charging region 42 of the charging roller 40 can be charged. The region can be uniformly charged.

In addition, in this Example 1, the line for lighting (intensity) correction is not limited to the LED of two lines (first line L1 to second line L2), and may be one or three or more lines. It may be configured to form a lighting (intensity) correction line.

Further, the three LED heads 51 are parallel to the main scanning direction MSD, in other words, parallel to the axis of the photoconductor 11, and their ends on which a plurality of LEDs 51a are arranged overlap each other in the sub scanning direction SSD. It is located in.
In each LED head 51, as shown in FIG. 4, 7296 LEDs 51a are arranged side by side in a straight line in the first embodiment.
The LED head 51 arranged in the center of the three LED heads 51 does not use 56 LEDs 51a (indicated by white circles in FIG. 4) from each end of both ends and is always turned off. deep.
Further, the two LED heads 51 on both sides of the three LED heads 51 have 44 LEDs 51a (in FIG. 4 in FIG. 4) from the end of one end portion on the overlapping side in the sub-scanning direction SSD with the central LED head 51. (Indicated by white circles) is not used for exposure and is always turned off.

In this way, the plurality of LEDs 51a (indicated by black circles in FIG. 4) of the three LED heads 51 are continuously arranged at equal intervals in the main scanning direction MSD.
Therefore, by using a plurality of highly versatile small-sized LED heads 51, it is possible to cover a long exposure range in the main scanning direction MSD at low cost.

In the first embodiment, the plurality of LEDs 51a (LEDs indicated by black circles in FIG. 4) arranged in the range of arrows W1 and W2 in FIG. 4 are LEDs 51a corresponding to the area where the three charging rollers 40 overlap. ing.

The developing unit 12 is a developing roller that is supported by a frame with a predetermined distance between the toner accommodating unit 12a containing toner of a predetermined color and the photoconductor 11, and is in contact with the photoconductor 11 during actual operation. It has 12b and.
The electrostatic latent image formed on the surface of the photoconductor 11a by the exposure unit 50 is visualized by developing the toner by the developing unit 12.

The photoconductor cleaner 13 is composed of a rubber blade or the like, and removes unnecessary toner or foreign matter remaining on the photoconductor 11.

Next, the transfer unit 14 will be described.
The transfer unit 14 includes a transfer belt 14a, a belt drive roller 14b, a belt tension roller 14c, a primary transfer roller 14d, and a belt cleaner 14e.

The transfer belt 14a is an endless belt, and is stretched by being hung on a belt drive roller 14b, a belt tension roller 14c, and a primary transfer roller 14d.

The belt drive roller 14b is driven by a drive unit (not shown) to rotate a belt tension roller 14c that is driven and rotated, and a transfer belt 14a that is hung by a primary transfer roller 14d.

The belt tension roller 14c adjusts the tension of the transfer belt 14a and prevents the transfer belt 14a from meandering.

The primary transfer roller 14d is arranged to face the photoconductor 11 of each color-coded unit 10 with the transfer belt 14a interposed therebetween, and is developed on the photoconductor 11 by applying a bias having a polarity different from the charging polarity of the toner. The toner image is electrostatically transferred to the transfer belt 14a.

The belt cleaner 14e removes unnecessary toner or foreign matter remaining on the transfer belt 14a.

Next, the transport unit 15 will be described.
The transport unit 15 transports the transfer material P such as paper from the supply unit to the fixing device in a state where the toner image is transferred.
The transport unit 15 has a plurality of transport rollers 15a arranged in the transport direction and a roller drive unit (not shown) for driving the transport rollers 15a, and the secondary transfer roller 15b is one of the transport rollers 15a. It is provided.
The secondary transfer roller 15b is arranged to face the transfer belt 14a with a transfer material P such as paper sandwiched between them, and is transferred onto the transfer belt 14a by applying a bias having a polarity different from the charging polarity of the toner. The toner image is transferred to a transfer material P such as paper.

The fixing unit 16 heats the toner image transferred to the transfer material P such as paper.

Here, a method of applying a DC voltage to each charging roller 40 will be described.
On the nip inlet side of the photoconductor 11 and the charging roller 40, the gap between the charging roller 40 and the photoconductor 11 gradually narrows, and the potential difference between the charging roller 40 and the photoconductor 11 becomes larger than the discharge start voltage. Then, a discharge is generated, the photoconductor 11 is charged until the potential difference between the charging roller 40 and the photoconductor 11 becomes the same value as the discharge start voltage, and when the potential difference becomes equal to or higher than the discharge start voltage, a linear charging characteristic with a slope of 1 is exhibited. ..
On the other hand, since the discharge start voltage fluctuates greatly depending on the environment such as temperature or atmospheric pressure and durability, the charging potential also fluctuates greatly.

Therefore, the image forming apparatus 1 of the first embodiment timely detects the discharge start voltage from each charge roller 40 to the photoconductor 11 as the DC voltage applied to each charge roller 40, and sets the detected discharge start voltage in advance. A predetermined voltage, for example, a DC voltage to which a voltage of 500 V is added is applied to each charging roller 40.

Further, the method of applying a voltage obtained by superimposing an AC voltage on a DC voltage to the charging roller 40 solves the problem of applying only the DC voltage and generates ozone, which is the greatest advantage of the contact type charging method. Regarding the effect of suppressing the ozone, the amount of ozone generated increases as compared with the case where only the DC voltage is applied, but the amount of ozone generated can be reduced by an order of magnitude as compared with the corona charging method.
When a voltage obtained by superimposing an AC voltage on a DC voltage is applied to the charging roller 40, instead of applying a constant peak-to-peak voltage VPP, the environment and durability, that is, contamination due to the durability of the charging roller 40, and further, Detects the minimum required inter-peak voltage that can respond to changes in film thickness due to the durability of the photoconductor 11, that is, the minimum required inter-peak voltage that satisfies the peak voltage VPP that is at least twice the discharge start voltage. Therefore, it is important to apply the minimum required inter-peak voltage VPP each time.

Next, the input unit 60 will be described. The input unit 60 is realized by a touch panel, and the operator inputs various setting information related to printing such as print settings.

In the image forming apparatus 1 of the first embodiment, the input unit 60 is also used to input the density step correction information necessary for correcting the density step of the print output image by the charging potential difference adjusting unit 71 described later. ..
The density step correction information means that the charging potential difference adjusting unit 71 corresponds to the charging potential of the photoconductor surface 11a corresponding to the region where the adjacent charging rollers 40 overlap and the photosensitive region corresponding to the region where the adjacent charging rollers 40 do not overlap. This is information necessary for executing control to reduce the difference between the body surface 11a and the charging potential.

The density step correction information is, for example, the LED of the LED 51a (a plurality of LEDs 51a indicated by black circles arranged in the ranges W1 and W2 in FIG. 4) related to the charging potential of the photoconductor surface 11a corresponding to the region where the adjacent charging rollers 40 overlap. The selection setting information and the lighting intensity of each of the selected and set plurality of LEDs 51a (hereinafter referred to as the selection LED) for each pixel are set to a plurality of LEDs 51a (hereinafter, non-selection LEDs) corresponding to the area where the adjacent charging rollers 40 do not overlap. This is LED lighting intensity setting information that is larger than that of ().

This density step correction information is stored in the storage unit 61 and used as control information by the charging potential difference adjusting unit 71.
Such input setting of density difference correction information is performed, for example, at the time of maintenance of the image forming apparatus 1.
More specifically, while changing the input setting of each density step correction information by the input unit 60, that is, the LED selection setting and the LED lighting intensity setting, the pattern in the input setting of each density step correction information. The input setting value of the density step correction information for which the print output image is confirmed and it is visually confirmed that the density step has been eliminated is stored in the storage unit 61 as determination information.

The storage unit 61 is composed of a well-known volatile memory or the like, and stores various information related to the operation of the image forming apparatus.
In the first embodiment, the storage unit 61 stores the above-mentioned density step correction information input by the input unit 60.

The control unit 70 is realized by a CPU or the like, and is electrically connected to each unit of the image forming apparatus 1.
The control unit 70 is a feature portion of the present invention, and is a photoconductor surface corresponding to a region where adjacent charging rollers 40 overlap and a charging potential of the photoconductor surface 11a corresponding to a region where adjacent charging rollers 40 do not overlap. It has a charging potential difference adjusting unit 71 that controls the exposure amount by the exposure unit 50 so as to reduce the difference from the charging potential of 11a.

The charging potential difference adjusting unit 71 controls lighting and extinguishing of the plurality of LEDs 51a.
The charging potential difference adjusting unit 71 acquires the above-mentioned LED selection setting information and LED lighting intensity setting information from the density step correction information stored in the storage unit 61, and lights a plurality of LEDs 51a based on this information. And controls turning off.

More specifically, the LED selection setting of the LEDs 51a (a plurality of LEDs 51a indicated by black circles arranged in the ranges W1 and W2 in FIG. 4) related to the charging potential of the photoconductor surface 11a corresponding to the region where the adjacent charging rollers 40 overlap. The information is correction information for correcting the position error of the ranges W1 and W2 of the LED 51a, which are slightly different for each machine due to the dimensional accuracy and the like.
The LED lighting intensity setting information refers to the LED 51a (ranges W1 and W2 in FIG. 4) related to the charging potential of the photoconductor surface 11a corresponding to the overlapping portion of the adjacent charging rollers 40, and is lit on the first line L1 in the range W1. Time to turn on (second line L2 is off), time to turn on on second line L2 in range W2 (first line L1 is off), charging of the photoconductor surface 11a corresponding to a region where a plurality of charging rollers 40 do not overlap In the LED 51a related to the electric potential (range other than the ranges W1 and W2 in FIG. 4), it is information that both the first line L1 and the second line L2 are turned off.

By controlling the lighting and extinguishing of the plurality of LEDs by the charging potential difference adjusting unit 71 in this way, the image forming apparatus 1 is exposed to light including the overlapping portion W of the charging region 42 of the charging roller 40 as shown in FIG. The charged region of the body surface 11a can be uniformly charged.
Specifically, when the charging potential of the photoconductor surface 11a of the non-overlapping portion of the charging roller 40 is −500V, the charging potential of the photoconductor surface 11a of the overlapping portion W of the charging roller is −550V, but the selection LED 51a By increasing the lighting intensity in one pixel with respect to the lighting intensity in one pixel of the non-selective LED 51a, the charging potential of −550 V can be eliminated to −500 V.
As a result, as shown in FIG. 13, the image forming apparatus 1 can eliminate the density difference caused by the overlapping portion W of the charging rollers 40 at each printing density.
In the graph in FIG. 12, the vertical axis (Y) indicates the surface potential of the photoconductor 11 with the negative charging direction facing upward, and the horizontal axis (X) indicates the axial position of the photoconductor 11.
Further, in the graph in FIG. 12, the solid line A shows the primary charge position (dark part potential), the broken line B shows the halftone potential, and the alternate long and short dash line C shows the bright part potential.

The image forming apparatus 1 according to the first embodiment of the present invention charges the photoconductor surface 11a by coming into contact with the photoconductor surface 11a that is moved by a rotational operation about the rotation axis of the photoconductor 11. Since three charging rollers 40 are provided along the direction intersecting the moving direction of the photoconductor surface 11a so that the ends of the adjacent charged regions 42 overlap each other in the moving direction of the photoconductor surface 11a, 3 The charged region can be covered in the axial direction of the photoconductor 11 by the two charging rollers 40.
Further, in the image forming apparatus 1 according to the first embodiment of the present invention, the exposure unit 50 does not overlap the exposure amount of the photoconductor surface 11a charged by the overlapping portion of the adjacent charging rollers 40 with the adjacent charging rollers 40. Since the exposure amount is larger than the exposure amount of the photoconductor surface 11a charged in the portion, the charging potential of the photoconductor surface 11a corresponding to the region where the adjacent charging rollers 40 overlap and the adjacent charging roller 40 do not overlap. The difference from the charging potential of the photoconductor surface 11a corresponding to the region can be reduced.
Therefore, the image forming apparatus 1 according to the first embodiment of the present invention can uniformly charge the long photoconductor 11, that is, can obtain a uniform image without an image density step. , Charging rollers 40 having different shapes can be applied including individual differences.

Further, in the image forming apparatus 1 according to the first embodiment of the present invention, a plurality of LEDs 51a arranged in parallel with the axis of the photoconductor 11 are used as a light source, and the charging potential difference adjusting unit 71 turns on and off the plurality of LEDs 51a. By controlling, the difference between the charging potential of the photoconductor surface 11a corresponding to the region where the three charging rollers 40 overlap and the charging potential of the photoconductor surface 11a corresponding to the region where the three charging rollers 40 do not overlap is reduced. Since the exposure amount by the exposure unit 50 is controlled so as to be performed, the exposure unit 50 using the LED head can be applied.

Further, in the image forming apparatus 1 according to the first embodiment of the present invention, the three charging rollers have an inclination angle A with respect to the direction in which the two charging rollers 40 are orthogonal to the moving direction of the photoconductor surface 11a in the rotation axis direction. Since the photoconductor 11 is attached to the photoconductor 11, the tilt angle A corresponding to the charging rollers 40 having different shapes is set including individual differences, so that the photoconductor 11 can be formed on the overlapping portion W of the charging region 42 of the charging roller 40. It can be charged uniformly.
Therefore, the image forming apparatus 1 according to the first embodiment of the present invention uniformly charges the photoconductor 11 with respect to the overlapping portion W of the charging region 42 of the charging roller 40 by adjusting the inclination angle A of the charging roller 40. At the same time, the charging potential difference adjusting unit 71 can charge the photoconductor 11 more stably and uniformly. That is, a uniform image with no difference in image density can be obtained.

Further, in the image forming apparatus 1 according to the first embodiment of the present invention, since the three charging rollers 40 are provided so that the inclination angles A can be adjusted within a predetermined range, the optimum angles A with respect to the individual charging rollers 40 from the initial stage. In addition, it is possible to adjust the mechanical difference and individual difference, and if it is durable and a charging step that did not occur at the initial inclination angle A occurs in the overlapping portion W of the charging region 42 of the charging roller 40. However, the problem can be easily remedied by readjusting the tilt angle A. As a result, the image forming apparatus 1 according to the first embodiment of the present invention can stably and uniformly charge the long photoconductor 11 even in long-term use.
In addition, charging rollers 40 having different shapes can be applied including individual differences.

Further, in the image forming apparatus 1 according to the first embodiment of the present invention, the charging potential difference adjusting unit 71 sets the lighting intensity of the LED 51a for each pixel of the electrostatic latent image formed on the photoconductor surface 11a by the adjacent charging roller 40. The LED 51a related to the charging potential of the photoconductor surface 11a corresponding to the overlapping region is larger than the LED 51a related to the charging potential of the photoconductor surface 11a corresponding to the region where the adjacent charging rollers 40 do not overlap. Since the lighting and extinguishing of the LED 51a is controlled, by adjusting the lighting intensity (number of lighting lines and lighting time) of each LED for forming one pixel, the photosensitivity corresponding to the area where the plurality of charging rollers 40 overlap The difference between the charging potential of the body surface 11a and the charging potential of the photoconductor surface 11a corresponding to the region where the plurality of charging rollers 40 do not overlap can be reduced.

Further, in the image forming apparatus 1 according to the first embodiment of the present invention, the exposure unit 50 has three LED heads 51 in which a plurality of the LEDs 51a are arranged in a straight line, and the photoconductor is formed by the three LED heads 51. Since the exposure range in the axial direction of 11 is covered, it is possible to use a highly versatile small-sized LED head without using a long LED head 51, and it is possible to reduce the cost.

Next, the image forming apparatus 2 according to the second embodiment of the present invention will be described with reference to FIGS. 14-16.
FIG. 14 is a diagram schematically showing the entire structure including the control unit 90 of the image forming apparatus 2 according to the second embodiment of the present invention. FIG. 15 is an enlarged view of the periphery of the photoconductor 11 of the image forming apparatus 2 shown in FIG. FIG. 16 is a diagram for explaining the positional relationship between the exposure unit 50, the three charging rollers 40, the photoconductor 11, and the surface potential detection unit 80.

The image forming apparatus 2 according to the second embodiment of the present invention is different from the image forming apparatus 1 of the first embodiment in that it has a surface potential detecting unit 80 for detecting the potential of the photoconductor surface 11a.
The other configurations are the same as those in the first embodiment, and the same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

The image forming apparatus 2 according to the second embodiment of the present invention includes four color-coded units 10, a transfer unit 14 that transfers a toner image to a transfer material P such as paper, and a transfer unit 15 that conveys the transfer material P. , The operation of the fixing unit 16 for fixing the toner image transferred to the transfer material P, the input unit 60 for inputting various setting information related to printing, the storage unit 61, the surface potential detecting unit 80, and each unit of the image forming apparatus 2. It has a control unit 90 for controlling the above.

The surface potential detection unit 80 is realized by the surface potential sensor 81, detects the potential of the photoconductor surface 11a, and outputs the detected potential to the control unit 90.
In the second embodiment, the surface potential detection unit 80 has six surface potential sensors 81.
Each surface potential sensor 81 is provided on the downstream side of the exposed portion 50 in the rotation direction of the photoconductor 11, and as shown in FIG. 16, the photoconductor surface 11a corresponding to the region where the three charging rollers 40 overlap, and the photoconductor surface 11a, and The three charging rollers 40 are dispersed and arranged parallel to the axial direction of the photoconductor 11 so that the potential of the photoconductor surface 11a corresponding to the non-overlapping region can be measured.
In the second embodiment, the surface potential detection unit 80 has six surface potential sensors 81, but the number of surface potential sensors 81 is not limited to six. That is, any other number may be used as long as the charging potential difference adjusting unit 91, which will be described later, can acquire the potential information to the extent that the LED lighting intensity setting information can be automatically generated.

The control unit 90 is realized by a CPU or the like, and is electrically connected to each unit of the image forming apparatus 2.
The control unit 90 is a feature of the present invention, and is a photoconductor surface corresponding to a region where adjacent charging rollers 40 overlap and a charging potential of the photoconductor surface 11a corresponding to a region where adjacent charging rollers 40 do not overlap. It has a charging potential difference adjusting unit 91 that controls the exposure amount by the exposure unit 50 so as to reduce the difference from the charging potential of 11a.
Specifically, the charging potential difference adjusting unit 91 corresponds to the lighting intensity of the LED 51a related to the charging potential of the photoconductor surface 11a corresponding to the region where the adjacent charging rollers 40 overlap, and corresponds to the region where the adjacent charging rollers 40 do not overlap. The lighting and extinguishing of the plurality of LEDs 51a are controlled so as to be larger than the LEDs 51a related to the charging potential of the photoconductor surface 11a.

More specifically, regardless of the latent image data, the LED 51a (ranges W1 and W2 in FIG. 16) related to the charging potential of the photoconductor surface 11a corresponding to the overlapping portion of the adjacent charging rollers 40 is the first in the range W1. The photoconductor surface 11a corresponds to a region where the plurality of charging rollers 40 do not overlap, with the 1st line L1 lit (the 2nd line L2 is extinguished) and the 2nd line L2 lit in the range W2 (the 1st line L1 is extinguished). In the LED 51a (range other than the ranges W1 and W2 in FIG. 16) related to the charging potential of the above, both the first line L1 and the second line L2 are turned off.

Since the first line L1 to the second line L2 are provided in this way, the charging potential difference adjusting unit 91 adjusts the lighting time of the first line L1 to the second line L2 to charge the charging roller 40. The charged region of the photoconductor surface 11a including the overlapping portion W of the region 42 can be uniformly charged, and the charged region of the photoconductor surface 11a including the overlapping portion W of the charging region 42 of the charging roller 40 can be uniformly charged. Can be made to.

The charging potential difference adjusting unit 91 controls lighting and extinguishing of the plurality of LEDs 51a based on the density step correction information stored in the storage unit 61.

In the density step correction information, the charging potential difference adjusting unit 91 corresponds to the charging potential of the photoconductor surface 11a corresponding to the region where the adjacent charging rollers 40 overlap and the photoconductor surface 11a corresponding to the region where the adjacent charging rollers 40 do not overlap. This is the information necessary to execute the control to reduce the difference from the charging potential of.

This density step correction information is the potential information of the photoconductor surface 11a detected from each surface potential sensor 81 of the surface potential detection unit 80.
The density step correction information is distributed so that the potentials of the photoconductor surface 11a corresponding to the region where the adjacent charging rollers 40 overlap and the photoconductor surface 11a corresponding to the region where the adjacent charging rollers 40 do not overlap can be measured. It is the information of the potential detected from each surface potential sensor 81.

Such density difference correction information is stored in the storage unit 61 and used as control information by the charging potential difference adjusting unit 91.

The storage process of the density step correction information in the storage unit 61 is performed, for example, at the time of maintenance of the image forming apparatus 2 or at the time of turning on the power.
For example, the input unit 60 is provided with an execution switch for storing the density step correction information, and by pressing this execution switch, the surface potential detection unit 80 automatically detects the potential of the photoconductor surface 11a by each surface potential sensor 81. Then, the information of the detected potential is stored in the storage unit 61.

The charging potential difference adjusting unit 91 is based on the concentration step correction information stored in the storage unit 61, and the LED 51a related to the charging potential of the photoconductor surface 11a corresponding to the region where the adjacent charging rollers 40 overlap (range W1 in FIG. 16). , The LED selection setting information of the plurality of LEDs 51a) indicated by black circles arranged in W2, and the lighting intensity of each of the selected and set plurality of LEDs 51a for each pixel, the plurality of LEDs 51a corresponding to the area where the adjacent charging rollers 40 do not overlap. The LED lighting intensity setting information to be increased in comparison with the above is automatically generated, and the lighting and extinguishing of the plurality of LEDs 51a are controlled.

The image forming apparatus 2 according to the second embodiment of the present invention has the same effect as the image forming apparatus 1 of the first embodiment, and the potential of the photoconductor surface 11a detected by the charging potential difference adjusting unit 91 by the surface potential detecting unit 80. The difference between the charging potential of the photoconductor surface 11a corresponding to the region where the adjacent charging rollers 40 overlap and the charging potential of the photoconductor surface 11a corresponding to the region where the adjacent charging rollers 40 do not overlap is reduced. Since it is possible to control the lighting and extinguishing of a plurality of LEDs 51a, as a result, while changing the LED lighting intensity setting, the print output image of the pattern in each density difference correction information input setting is confirmed. It is possible to omit the complicated work of storing the input set value of the density step correction information for which it is visually confirmed that the density step has been eliminated in the storage unit 61 as the determination information.

The image forming apparatus 1 and 2 according to the first and second embodiments of the present invention exemplify the straight-shaped charging roller 40, but the shape of the charging roller 40 is not limited to this, and other shapes may be applied. Can be done. For example, as shown in FIG. 17, a crown shape (see FIG. 17 (a)) or an inverted crown shape (see FIG. 17 (b)) can also be applied.

Further, in the image forming apparatus 1 and 2 according to the first and second embodiments of the present invention, one central charging roller 40 is provided so that the rotation axis direction is orthogonal to the moving direction of the photoconductor surface 11a, and both sides thereof. An example is shown in which the two charging rollers 40 are provided with an inclination angle A with respect to a direction in which the rotation axis direction is orthogonal to the moving direction of the photoconductor surface 11a, but the present invention is not limited to this.
For example, as shown in FIG. 18, all three charging rollers 40 may be provided with an inclination angle A (see FIG. 18A), and one charging roller 40 in the center may be provided in the rotation axis direction. An inclination angle A is provided with respect to a direction orthogonal to the moving direction of the photoconductor surface 11a, and two charging rollers 40 on both sides are provided so that the rotation axis direction is orthogonal to the moving direction of the photoconductor surface 11a. (See FIG. 18 (b)).
Further, all three charging rollers 40 are not provided with an inclination angle A, and all three charging rollers 40 are provided so that the rotation axis direction is orthogonal to the moving direction of the photoconductor surface 11a. It does not matter (see FIG. 18 (c)).

Further, in the image forming apparatus 1 and 2 according to the first and second embodiments of the present invention, the charging unit 20 has three charging rollers 40, but the number of charging rollers 40 is not limited to three and may be plural. Just do it. For example, the number of charging rollers 40 may be two or four or more.

Further, the image forming apparatus 1 and 2 according to the first and second embodiments of the present invention illustrate that the tilt angle A of the charging roller 40 can be adjusted within a predetermined range, but the tilt angle A is fixed to one value. You may be.
For example, the device specifications may be fixed to the determined inclination angle A by determining the optimum inclination angle A corresponding to the shape of the charging roller 40 such as the crown shape, the straight shape, and the inverted crown shape. ..

Further, in the image forming apparatus 1 and 2 according to the first and second embodiments of the present invention, the exposure unit 50 uses a plurality of LEDs as a light source, but the exposure unit 50 uses a light source other than the LED. You may. For example, a point light source may be provided separately from the LED head and used in combination, or a surface emitting semiconductor laser element may be applied.

The invention made by the present inventor has been specifically described above based on the above-mentioned examples of the invention, but the present invention is not limited to the above-mentioned examples of the invention and does not deviate from the gist thereof. Can be changed in various ways.

1, 2 Image forming device 10 Color-coded unit 11 Photoreceptor 11a Photoreceptor surface 12 Development unit 12a Toner storage unit 12b Development roller 13 Photoreceptor cleaner 14 Transfer unit 14a Transfer belt 14b Belt drive roller 14c Belt tension roller 14d Primary transfer roller 14e Belt cleaner 15 Conveying part 15a Conveying roller 15b Secondary transfer roller 16 Fixing part 17 Cleaning roller 17a Metal shaft part 17b Cleaning material 20 Charging part 21 Bearing part 22 Fixed part 22a Spring accommodating part 22b Guide wall part 22c Guide protrusion 23 Movable Bearing part 24 Electrode holding part 25 Axial urging member holding part 25a, 25b Axial urging member 26 Axial end rotation support part 27, 28 Metal shaft part holding recess 30 Fixed frame 31 Fixed part 32 Multiple charging roller arrangement part 32a Bearing fixing surface 33 Screw fixing part 34 Angle adjustment guide slit 40 Charging roller 41 Metal shaft part 42 Elastic contact part (charged area)
50 Exposure section 51 LED head 51a LED
60 Input unit 61 Storage unit 70, 90 Control unit 71, 91 Charging potential difference adjusting unit 80 Surface potential detection unit 81 Surface potential sensor A Tilt angle B Difference in axis center position between both ends of the charging roller D D Photoconductor and charging roller Distance between shaft centers E Electrode plate P Transfer material such as paper R1 Radius of photoconductor R2 Radius of charging roller S Spring T Cross amount W1, W2 Overlapping part

Claims (7)

A charged portion having a charging roller that charges the surface of the photoconductor by contacting the photoconductor and the surface of the photoconductor that is moved by a rotation operation about the rotation axis of the photoconductor, and a charged portion charged by the charged portion. In an image forming apparatus including an exposed portion that exposes the photoconductor to form an electrostatic latent image.
The charged part is
A plurality of the charging rollers are provided along the direction intersecting the moving direction of the photoconductor surface so that the ends of the adjacent charged regions overlap in the moving direction of the photoconductor surface.
The exposed part
The exposure amount of the photoconductor surface charged by the overlapping portions of the plurality of charging rollers is made larger than the exposure amount of the photoconductor surface charged by the non-overlapping portions of the plurality of charging rollers. Image forming device. The exposed part
A plurality of LEDs arranged in parallel with the axis of the photoconductor are used as a light source.
The image forming apparatus
By controlling the lighting and extinguishing of the plurality of LEDs, the charging potential on the surface of the photoconductor corresponding to the region where the plurality of charging rollers overlap and the photoconductor corresponding to the region where the plurality of charging rollers do not overlap. The image forming apparatus according to claim 1, further comprising a charging potential difference adjusting unit that controls an exposure amount by the exposed unit so as to reduce the difference from the charging potential on the surface. The plurality of charging rollers
The image forming apparatus according to claim 1 or 2, wherein one or more of the charging rollers are provided at an inclination angle with respect to a direction in which the rotation axis direction is orthogonal to the moving direction of the surface of the photoconductor. The plurality of charging rollers
The image forming apparatus according to claim 3, wherein the inclination angle is adjustable within a predetermined range. The charging potential difference adjusting unit is
The lighting intensity of the LED for each pixel of the electrostatic latent image formed on the surface of the photoconductor is set to the plurality of LEDs related to the charging potential of the surface of the photoconductor corresponding to the region where the plurality of charging rollers overlap. 2, 3 The present invention is characterized in that the lighting and extinguishing of the plurality of LEDs are controlled so as to be larger than the LEDs related to the charging potential on the surface of the photoconductor corresponding to the region where the charging rollers do not overlap. Or the image forming apparatus according to 4. The exposed part
Claims 2, 3, and 4, wherein the plurality of LEDs have a plurality of LED heads arranged side by side in a straight line, and the plurality of LED heads cover the exposure range in the axial direction of the photoconductor. Or the image forming apparatus according to 5. Further having a surface potential detecting unit for detecting the potential on the surface of the photoconductor,
The charging potential of the photoconductor surface corresponding to the region where the plurality of charging rollers overlap based on the potential detected by the surface potential detection unit, and the photoconductor surface corresponding to the region where the plurality of charging rollers do not overlap. The image forming apparatus according to claim 1, 2, 3, 4, 5 or 6, wherein the exposure amount by the exposed portion is controlled so as to reduce the difference from the charging potential of the image.

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