JP2008039992A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid image misalignment caused by deviation of toner image conveyance timing and transfer material conveyance timing when an intermediate transfer belt having an elastic layer is used as an intermediate transfer member.
SOLUTION: An intermediate transfer body position detecting unit is provided opposite to an outer roller that bends the intermediate transfer belt inward from the image carrying surface, and detects a home position flag of the intermediate transfer belt. The home position flag is attached to the back surface of the base layer having a higher elastic modulus.
[Selection] Figure 1

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile, which employs an image forming system such as an electrophotographic system, and forms a monocolor or full color image.

  An example of a conventional image forming apparatus employing an electrophotographic system is shown in FIG.

  The surface of the photoreceptor drum 1y is uniformly charged by the charging roller 3y, and an electrostatic latent image is formed on the surface by receiving laser irradiation corresponding to image information by the laser driver 2y. The electrostatic latent image is visualized by electrostatically attaching the charged yellow toner by the developing unit 4y corresponding to the yellow component. The toner image on the photosensitive drum 1y is electrostatically primary transferred onto the intermediate transfer member 5 by the primary transfer roller 6y.

  The above-described color component forming process is similarly performed for the remaining magenta, cyan, and black color components, so that a full-color image is formed on the intermediate transfer member 5.

  Further, the secondary transfer roller 82 electrostatically performs secondary transfer onto the transfer material P conveyed at a predetermined timing. The transfer material onto which the toner image has been transferred is conveyed to the fixing unit 9 and is subjected to heat fixing to form a permanent image.

  The intermediate transfer member 5 is stretched by a plurality of rollers 101, 102, and 103. In particular, reference numeral 103 denotes a stretching roller called an outer roller that bends the intermediate transfer member inward from the toner carrying surface side. The fixing device 9 can be disposed in an empty space by bending the intermediate transfer member 5 inward by the outer roller 103, and the image forming apparatus can be downsized.

  In the image forming apparatus as described above, if the feeding timing at which the transfer material P is transported deviates from the timing at which the toner image on the intermediate transfer body 5 is transported, image misalignment occurs. In order to avoid this, a technique is known in which a position detection pattern based on a toner image is formed on the intermediate transfer member 5, the position detection pattern is detected by the home position sensor S, and the deviation amount is fed back and corrected. It is. (For example, refer to Patent Document 1). Alternatively, a technique in which intermediate transfer body position detection means is provided in advance on the toner carrying surface or non-toner carrying surface of the intermediate transfer body and detection is performed by the position detection means is also known. (For example, refer to Patent Document 2).

As described above, when the position detection unit on the intermediate transfer member is detected by the detection unit, the intermediate transfer member is stretched at a position facing the home position sensor S as in the image forming apparatus having the above configuration. As a result, the distance between the home position sensor S and the intermediate transfer member 5 is regulated, so that the position of the intermediate transfer member can be detected stably.
Japanese Patent Laid-Open No. 11-194561 JP-A-8-137168

  However, when a belt having at least one elastic layer is used as the intermediate transfer member, the position of the intermediate transfer member may not be properly detected for the following reason.

  As shown in FIG. 4, regarding the intermediate transfer member 5 having a two-layer structure, the thickness of the surface layer 52 is d2, the thickness of the base layer 51 is d1, and the radius of the stretching roller 101 is r. At this time, when the intermediate transfer member 5 is wound around the stretching roller 101 by an angle b, the winding length of the outermost surface of the intermediate transfer member is (r + d1 + d2) × b. On the other hand, the winding length of the lowermost surface of the intermediate transfer member 5 at this winding portion is r × b. For this reason, since the length differs by (d1 + d2) × b, which is the difference between the outermost surface and the lowermost surface of the intermediate transfer member, the entire intermediate transfer member extends as it approaches the outermost surface. Thus, the distribution of elongation occurs in the thickness direction of the intermediate transfer belt 5.

  On the other hand, in the image forming apparatus as shown in FIG. 3, the primary transfer unit that actually forms the toner of each color component on the intermediate transfer member 5 may not be wound as much as the stretching roller 101. . For example, the primary transfer portion in the black toner station is configured as shown in FIG. 5, in which 1k is a photosensitive drum, 6k is a primary transfer roller, 52 is a surface layer, and 51 is a base layer. In such a case, since the belt is stretched straightly and used for the primary transfer portion, there is no difference in length between the outermost surface of the belt and the lowermost surface. There is no distribution of elongation.

  At this time, image formation is performed under conditions different from the state of the outermost layer of the intermediate transfer body 5 detected in the state of being stretched by the stretching roller 101, and the intermediate transfer body detected by the stretching roller 101. 5 cannot be referred to, and there is a risk that image displacement will occur.

  In addition to the configuration shown in FIG. 3, in order to detect the position of the intermediate transfer member 5, a stretch member of the intermediate transfer member 5 is used at a position facing the home position sensor S as position detection means. In the full-color image forming apparatus capable of forming images of a plurality of colors, it is necessary to make the tension structure for detecting the position exactly the same as the primary transfer and the secondary transfer. There is a risk of complications.

  Accordingly, the present invention has been made in view of such a situation, and an image forming apparatus capable of effectively avoiding image misalignment even in a belt having at least one elastic layer as an intermediate transfer member. It is to provide.

The present invention
An image carrying belt that includes a position detection mark that indicates a position, rotates, and includes a plurality of layers;
Position detection mark detection means for detecting the position detection mark;
A first support member that contacts the first surface of the image bearing belt and supports the image bearing belt;
An image forming apparatus having a second support member that contacts the second surface on the back side of the first surface of the image bearing belt and supports the image bearing belt;
The position detection mark detection means is provided at a position facing the first support member via the image carrying belt,
The layer including the second surface among the plurality of layers is characterized by not having the lowest elastic modulus among the plurality of layers.

The present invention also provides
A plurality of position detection marks indicating the position, an image carrying belt composed of a plurality of layers,
Position detection mark detection means for detecting the position detection mark;
A first support member that contacts the first surface of the image bearing belt and supports the image bearing belt;
A second support member that contacts the second surface behind the first surface of the image bearing belt and supports the image bearing belt;
In an image forming apparatus having an image carrier belt driving means for driving the image carrier belt,
The position detection mark detection means is provided at a position facing the first support member via the image carrying belt,
The layer including the second surface among the plurality of layers is characterized by not having the lowest elastic modulus among the plurality of layers,
The image carrying belt driving means is controlled according to the detection result of the position detection mark.

  As is clear from the above, small-sized image formation that does not cause color misregistration over a long period of time by detecting the position of the intermediate transfer belt with high accuracy while improving the image quality and stability of the toner utilization rate. An apparatus can be provided.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent. Further, the materials, shapes, etc. of the members once described in the following description are the same as those in the first description unless otherwise described.

(Embodiment 1)
A schematic configuration of an electrophotographic full-color laser printer as an example of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG.

  This embodiment is an image forming apparatus that forms a full-color image by superimposing toner images of a total of four colors, yellow, magenta, cyan, and black.

  In the figure, reference numerals 1y to 1k denote photosensitive drums as image information carriers. The photoconductive drum is formed by forming a photoconductor having an organic photoconductor (OPC) as a main component on an aluminum cylinder having an outer diameter of 30 mm, and the surface is uniformly formed by the charging rollers 3y to 3k. After being charged, the laser beams 2y to 2k are irradiated to form an electrostatic latent image corresponding to each color component on the surface. In this embodiment, lasers having a wavelength of 700 nm are used as the lasers 2y to 2k, and the photosensitive drums 1y to 1k have a large sensitivity in this wavelength region. The driving of the lasers 2y to 2k is controlled by a laser driver (not shown).

  With respect to the formed electrostatic latent image, each color toner image is developed by toner developing devices 4y to 4k to become a visible image. The color toner images formed on the photosensitive drums 1y to 1k are primarily transferred onto the intermediate transfer belt 5 by the primary transfer rollers 6y to 6k. The surfaces of the photosensitive drums 1y to 1k having the respective color toner images transferred to the intermediate transfer belt 5 are cleaned by the photosensitive drum cleaners 7y to 7k, and are used for the next and subsequent image forming operations.

  The toner image formed on the intermediate transfer belt 5 is transported to the secondary transfer portion composed of the secondary transfer inner roller 81 and the secondary transfer outer roller 82, and onto the transfer material P transported at a predetermined timing. The images are collectively transferred and subjected to heat and pressure fixing by the fixing device 9 to form a permanent image.

  After the toner image is transferred to the transfer material, the intermediate transfer belt is cleaned by the intermediate transfer belt cleaner 10 and used for image formation from the next time.

  Hereinafter, the configuration of each member and the image forming conditions in the image forming unit that forms a visible image of yellow toner will be described.

  The yellow toner developing device 4y conveys yellow toner to the developing sleeve by a yellow toner conveying mechanism in a developing device (not shown), and applies a thin layer of yellow toner to the outer periphery of the developing sleeve by a regulating blade pressed against the outer periphery of the developing sleeve. Then, after the electric charge is applied to the yellow toner, the developing latent image formed on the photosensitive drum 1 is developed by applying a developing bias in which an AC bias is superimposed on a DC bias to the developing sleeve. The developing sleeve is disposed at a position facing the photosensitive drum 1 with a minute interval (300 μm).

  The intermediate transfer belt 5 has a three-layer configuration including a base layer 51, an elastic layer 52 formed on the surface of the base material, and a surface layer 53 formed on the surface of the elastic layer.

The base layer 51 uses a polyimide resin film having a thickness of 85 μm as a base material, disperses carbon black, and has a surface resistivity of 1 × 10 ¹² Ω / □ and a volume resistivity of 1 × 10 ^9.5 Ω · cm. The resistance was adjusted so that Moreover, the elastic modulus of the base material was adjusted to be 1.5 to 8 GPa. The peripheral length of the intermediate transfer belt was 895 mm, and the driving speed (process speed) was 274 mm / sec.

The elastic layer 52 is made of fluorine rubber. The elastic layer 15b has a volume resistivity of 10 ^9.5 Ωcm and a thickness of 250 μm. The elastic modulus of the elastic layer was adjusted to be 0.1 to 1000 MPa.

The surface layer 53 is preferably made of a material having a high toner releasability. In this embodiment, the surface layer 53 is made of PFA, and has a volume resistivity of 10 ¹² Ωcm and a thickness of 15 μm. The elastic modulus of the surface layer was adjusted to be 0.01 to 1 GPa.

  In this example, the elastic modulus was defined as the tensile elastic modulus. The tensile modulus test method conforms to JIS K7161, and the test piece conforms to JIS K7262. As test conditions, the measurement was performed using a desktop material testing machine STA-1225 manufactured by Orientec Co., Ltd., a crosshead speed of 100 mm / min, a test piece width of 5 mm, a test piece length of 100 mm, 23 ° C., 50 Performed in a% Rh environment.

The primary transfer roller 5 was a sponge roller provided with a foamed rubber layer made of foamed EPDM on a steel core with an outer diameter of 8 mm, and the outer diameter was 16 mm. The resistance of the roller was adjusted by dispersing an ion conductive resistance adjusting agent so that the resistance was 10 ^6.5 Ω (when 100 V was applied) in an environment of 23 ° C. and 50% Rh.

The secondary transfer outer roller 72 is a sponge roller in which a foamed rubber layer based on foamed NBR (nitrile butadiene rubber) is provided on a steel core with an outer diameter of 12 mm, and includes an NBR rubber layer. The outer diameter was 24 mm. The resistance of the roller was adjusted by dispersing an ion conductive resistance adjusting agent so as to be 10 ^7.5 Ω (when 2 kV was applied) in an environment of 23 ° C. and 50% Rh.

  In this embodiment, the intermediate transfer belt 5 is stretched by four rollers, and the driving roller 101 and the tension roller 102 are SUS rollers having an outer diameter of 30 mm and are grounded. The outer roller 103 is configured by coating PFA on the surface layer of a SUS roller having an outer diameter of 24 mm.

  In this embodiment, the intermediate transfer belt 5 is bent inward from the image carrying surface by the outer roller 103, and the fixing device 9 is provided in a space where there is room, thereby reducing the size of the image forming apparatus. realizable.

  In this embodiment, as shown in FIG. 2, the home position sensor S is a specular reflection type sensor that detects reflected light, and detects an intermediate transfer belt home position flag F attached to the back surface of the intermediate transfer belt. It is composed of an LED light source 201 disposed at a predetermined angle φ with respect to the position, and a phototransistor 202 as a light receiving element. The light receiving element 202 is disposed at a predetermined angle φ. Yes. The reflected light emitted from the LED light source 201 to the reference density pattern is detected by the light receiving element, thereby detecting the presence of the home position flag F and detecting the position information of the intermediate transfer belt 5 based on this information. Is possible.

  In this embodiment, each color component in the primary transfer unit is overlapped by feeding back to the feeding timing of the transfer material to the secondary transfer unit and the image forming timing based on the detected position information of the intermediate transfer belt 5. Control is performed to prevent color misregistration at the time, and to prevent color misregistration during secondary transfer on the transfer material.

  In this embodiment, the home position sensor S is characterized by facing the outer roller 103 of the intermediate transfer belt 5 through the intermediate transfer belt 5 as shown in FIG.

  This is because by attaching the home position flag F to the back surface of the intermediate transfer belt 5, it is possible to effectively avoid toner contamination of the home position flag even over a long period of use, and therefore, a highly accurate intermediate position over a long period of time. This is because the position of the transfer belt 5 can be detected.

  In this embodiment, the intermediate transfer belt 5 has a three-layer configuration of a base layer 51, an elastic layer 52, and a surface layer 53. This is because the intermediate transfer belt 15 is deformed in the thickness direction corresponding to the thickness of the toner image or the unevenness of the surface of the transfer material in the primary transfer portion and the secondary transfer portion by providing the elastic layer 52 having a low elastic modulus. By having the above structure, the transferability is improved, so that the image forming apparatus has a function of improving the image quality and improving the stability of the toner utilization rate. By using a resin layer having a higher elastic modulus as the base layer 51, it is possible to perform highly accurate rotational driving by suppressing deformation in the width direction of the belt. In the present embodiment, the home position flag F is attached not to the elastic layer side that greatly expands and contracts during rotational driving, but to the base layer side that has less expansion and contraction, thereby avoiding expansion and contraction of the home position flag F and high precision intermediate transfer. The position detection of the belt 5 can be realized.

  In the present embodiment, the distance between the home position sensor S and the home position flag F can be kept constant by performing detection at a portion stretched around the outer roller 103. If detection is to be performed in a place where the outer roller is not stretched, it is necessary to detect the position without the facing member, and the vibration of the intermediate transfer belt 5 causes the home position flag F and the home position sensor S to be detected. Since the distance may become unstable, the position detection of the intermediate transfer belt 5 with higher accuracy can be realized.

  Further, since the home position sensor S is disposed inside the space where the intermediate transfer belt 5 is stretched, the image forming apparatus can be prevented from being enlarged, and thus the image realized by the outer roller 103 is realized. There is also an advantage that miniaturization of the forming apparatus is not hindered.

  Accordingly, it is possible to provide a small-sized image forming apparatus that does not cause image misalignment over a long period of time by detecting the position of the intermediate transfer belt with high accuracy while improving the image quality and stability of the toner utilization rate. Is possible.

(Embodiment 2)
Next, a second embodiment of the present invention will be described.

FIG. 6 is a schematic configuration diagram of a color laser printer which is an example of the image forming apparatus according to the present embodiment. In the figure, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.
In the drawing, Fv is a home position flag affixed to the back surface of the intermediate transfer belt 5, and is affixed at regular intervals with respect to the driving direction of the intermediate transfer belt 5. In the present embodiment, the home position flag Fv has a rectangular shape and has a side having a length of 5 mm with respect to the driving direction of the intermediate transfer belt 5. A plurality of home position flags Fv are affixed. In this embodiment, the home position flags Fv are affixed over the entire back surface of the intermediate transfer belt 5 with an interval of 10 mm.

  Also in this embodiment, as in the first embodiment, the home position sensor S is disposed at a position facing the outer roller 103, and detects the position of the intermediate transfer belt 5 with high accuracy. Is possible.

  Furthermore, in this embodiment, by continuously detecting the home position flag Fv attached to the back surface of the intermediate transfer belt 5 at equal intervals, it is possible to directly detect the driving speed of the intermediate transfer belt 5 and uneven driving speed. It becomes possible. The detected driving speed of the intermediate transfer belt 5 and uneven driving speed are fed back to an intermediate transfer belt 5 driving means (not shown), and the driving speed can be adjusted as appropriate so as to obtain an appropriate driving speed. As a result, the driving speed of the intermediate transfer belt 5 can be stabilized with high accuracy, and image displacement can be avoided with higher accuracy.

It is the schematic of the 1st Embodiment of this invention. It is the schematic of a structure of a home position sensor. It is a schematic diagram of a conventional image forming apparatus. It is a figure for demonstrating the subject of the conventional image forming apparatus. It is a figure for demonstrating the subject of the conventional image forming apparatus. It is the schematic of the 2nd Embodiment of this invention.

Explanation of symbols

1y to 1k Photosensitive drum 2y to 2k Exposure unit 3y to 3k Charging unit 4y to 4k Developer 5 Intermediate transfer belt 51 Intermediate transfer member base layer 52 Intermediate transfer member elastic layer 6y to 6k Primary transfer roller 7y to 7k Photoreceptor drum cleaner 81 Secondary transfer inner roller 82 Secondary transfer outer roller 9 Fixing means 10 Intermediate transfer member cleaner 101, 102 Intermediate transfer member stretching roller 103 Outer roller 201 Light emitting element 202 Light receiving element F Intermediate transfer member position detecting means S Home position sensor

Claims (2)

An image carrying belt that includes a position detection mark that indicates a position, rotates, and includes a plurality of layers;
Position detection mark detection means for detecting the position detection mark;
A first support member that contacts the first surface of the image bearing belt and supports the image bearing belt;
An image forming apparatus having a second support member that contacts the second surface on the back side of the first surface of the image bearing belt and supports the image bearing belt;
The position detection mark detection means is provided at a position facing the first support member via the image carrying belt,
The image forming apparatus, wherein a layer including the second surface among the plurality of layers has the lowest elastic modulus among the plurality of layers. A plurality of position detection marks indicating the position, an image carrying belt composed of a plurality of layers,
Position detection mark detection means for detecting the position detection mark;
A first support member that contacts the first surface of the image bearing belt and supports the image bearing belt;
A second support member that contacts the second surface behind the first surface of the image bearing belt and supports the image bearing belt;
In an image forming apparatus having an image carrier belt driving means for driving the image carrier belt,
The position detection mark detection means is provided at a position facing the first support member via the image carrying belt,
The layer including the second surface among the plurality of layers is characterized by not having the lowest elastic modulus among the plurality of layers,
An image forming apparatus, wherein the image carrying belt driving unit is controlled in accordance with a detection result of the position detection mark.

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