JP2005221941A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which transfer blur in a first transfer position due to contact shock of a secondary transfer roller can be prevented. <P>SOLUTION: A first image forming part and a second image forming part are disposed around an image carrier. Each image forming part has two developing devices which can be switched. Each of the image forming parts performs the process in which latent images formed on an electrostatic latent image carrier with exposure by an exposure device are successively turned into toner images by the two developing devices and the toner images are transferred onto the image carrier by a first transfer means. The image forming apparatus transfers the plurality of toner images formed on the image carrier onto a recording medium all at once by a second transfer means which can be brought into contact with the image carrier or separated from it. The image forming apparatus satisfies the relation of Lb≥Lm, wherein Lb is a distance on the image carrier from the first transfer position to the second transfer position in the second image forming part in the direction of the movement of the image carrier, and Lm is the length of a recording material in the direction of its movement. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that sequentially superimposes and transfers toner images of respective colors formed in a plurality of image forming units onto an image carrier, and collectively transfers the toner images carried on the image carrier to a recording material. About.

  In recent years, the demand for color image printing has increased, and various color image forming apparatuses have been put into practical use. FIG. 4 shows a conventional example of an image forming apparatus called a so-called four-pass method, which is one of the representative methods.

  Hereinafter, it demonstrates along a figure.

  A photosensitive drum 1 as an electrostatic latent image carrier constituted by applying an organic photoreceptor (OPC) or a photoconductor made of A-Si, CdS, Se or the like to the outer peripheral surface of an aluminum cylinder is not shown. It is driven in the direction of the arrow in the figure by the driving means, and is uniformly charged to a predetermined potential by the charging roller 2. Next, the exposure device 3 scans the photosensitive drum 1 with light according to a signal in accordance with a yellow image pattern, and a latent image is formed on the photosensitive drum 1.

  Further, when the photosensitive drum 1 advances in the direction of the arrow, the developing device 4a, 4b, 4c, 4d supported by the support 5 is supported so that the developing device 4a containing yellow toner faces the photosensitive drum 1. 5 rotates and is visualized by the selected developing device 4a. The developed toner image is transferred onto an intermediate transfer belt 61 as an image carrier.

  The intermediate transfer belt 61 is made of rubber such as EPDM, NBR, urethane, silicone rubber, or resin such as PVdF, polyimide, polycarbonate, polyamide, polyethylene, and has three rollers: a driving roller 62, a driven roller 63, and a tension roller 64. The intermediate transfer belt 61 is driven in the direction of the arrow in the drawing by being stretched upward and the drive roller 62 being rotated in the direction of the arrow in the drawing by a motor (not shown).

  Reference numeral 65 denotes a primary transfer roller as a first transfer unit provided with a conductive sponge layer on a shaft, and is in contact with the photosensitive drum 1 through an intermediate transfer belt 61. A bias is applied to the primary transfer roller 65 from a high voltage power supply (not shown), and the toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt 61.

  By performing the above process for magenta, cyan, and black colors, toner images of a plurality of colors are formed on the intermediate transfer belt 61.

  When the four color toner images are transferred onto the intermediate transfer belt 61, the recording material P synchronized with the movement of the intermediate transfer belt 61 is conveyed. The secondary transfer roller 66 as the second transfer means that can be contacted and separated has the same configuration as the primary transfer roller 65, has a predetermined peripheral speed difference from the intermediate transfer belt 61, and is intermediate via the recording material P. A bias is applied from a high voltage power supply (not shown) in contact with the transfer belt 61, and the four-color toner images on the intermediate transfer belt 61 are collectively transferred onto the recording material P. The recording material P onto which the four-color toner image has been transferred is melted and fixed by a conventionally known heating and pressure fixing device 8 to obtain a color image.

  The transfer residual toner on the photosensitive drum 1 is cleaned by a known cleaning device 7 of blade means. Further, the transfer residual toner on the intermediate transfer belt 61 is also cleaned by a cleaning device 67 such as a fur brush or a web that can be contacted and separated.

  FIG. 5 shows a conventional example of an image forming apparatus called one-pass system or tandem system, which is one of other typical systems. In addition, in the figure, the same number is attached | subjected to what has the same structure and effect | action, and description about them is abbreviate | omitted.

  In this system, a plurality of image forming sections A, B, C, and D having a photosensitive drum, an exposure device, a charging roller, a developing device, and a cleaner are arranged around the transfer belt 61. Reference numerals 1a, 1b, 1c, and 1d denote photosensitive drums, which are charged by the charging rollers 2a, 2b, 2c, and 2d, respectively, and then the exposure apparatuses 3a, 3b, 3c, and 3c are respectively synchronized with the movement of the transfer belt 61. The image pattern is exposed by 3d to form a latent image. The formed latent images are developed by developing devices 4a, 4b, 4c, and 4d to be visualized as toner images, and are multiplexed on the intermediate transfer belt 61 by primary transfer rollers 65a, 65b, 65c, and 65d, respectively. Transcribed.

  The toner images of a plurality of colors transferred onto the transfer belt 61 are collectively transferred onto the recording material P synchronized with the transfer belt 61 by the secondary transfer roller 66. The recording material P onto which the four-color toner image has been transferred is melted and fixed by a conventionally known heating and pressure fixing device 8 to obtain a color image.

  Further, the residual toner on the photosensitive drums 1a, 1b, 1c, and 1d is cleaned by the cleaning devices 7a, 7b, 7c, and 7d. The secondary transfer residual toner on the intermediate transfer belt 61 is cleaned by a cleaning device 67. In this method, the secondary transfer roller 66 and the cleaning device 67 do not need a contact / separation function. In addition to the intermediate transfer method, a direct transfer method in which a recording material is directly supported on a belt and a toner image on each photosensitive drum is transferred onto the recording material by a transfer roller 65 has been put into practical use. ing.

  The two image forming apparatuses described above have the following characteristics.

  The four-pass method shown in FIG. 4 is a small and low-cost device because it is composed of a single photosensitive drum, an exposure device, a charging roller, a cleaning device, and a primary transfer roller. On the other hand, in order to obtain a full-color image, the intermediate transfer belt needs to rotate four times. Therefore, the intermediate transfer belt is not suitable for high-speed recording. Yes.

  On the other hand, the one-pass method shown in FIG. 5 requires a plurality of photosensitive drums, an exposure device, a charging roller, a cleaning device, and a primary transfer roller, which increases the size and cost of the device. . On the other hand, in order to obtain a full-color image, it is not necessary to rotate the intermediate transfer belt a plurality of times, and an apparatus suitable for high-speed recording and having a recording speed of 8 ppm or more in A4 size has been put into practical use.

  In recent years, a method having an intermediate characteristic between the two methods described above shown in FIG. In this method, two image forming portions are arranged around an intermediate transfer belt as an image carrier, and a full-color image can be obtained by rotating the intermediate transfer belt twice (this method is hereinafter referred to as a two-pass method). Call). In the following, description will be made with reference to FIG. 6, but those having the same configuration / action are denoted by the same reference numerals and description thereof will be omitted.

  Around the intermediate transfer belt 61, a first image forming unit A and a second image forming unit B, each including a photosensitive drum, an exposure device, a charging roller, two switchable developing devices, and a cleaning device, are disposed.

  Next, the image forming operation will be described in detail.

  In the image forming section A, the photosensitive drum 1a is charged by the charging roller 2a, and the first color yellow image exposure is performed by the exposure device 3a. The latent image formed on the photosensitive drum 1a is developed by the developing device 4a corresponding to the first color yellow. The developing devices 4a and 4c can be moved in the direction of the arrow in the figure by driving means (not shown), and the developing devices are switched. The developed yellow toner image is transferred onto the intermediate transfer belt 61 by the primary transfer roller 65a. The second color magenta image is formed in the image forming unit B so that the first color yellow toner image on the intermediate transfer belt 61 is aligned.

  In the image forming unit B, as in the first color yellow image formation in the image forming unit A described above, the photosensitive drum 1b is charged by the charging roller 2b, and the second color magenta image exposure is performed by the exposure device 3b. Done. The latent image formed on the photosensitive drum 1b is developed by the developing device 4b corresponding to the second color magenta. The developing devices 4b and 4d can be moved in the direction of the arrow in the drawing by a driving means (not shown), and the developing devices are switched.

  The developed magenta toner image is transferred onto the intermediate transfer belt 61 by the primary transfer roller 65b so as to be aligned with the first color yellow toner image on the intermediate transfer belt 61.

  When the development of the first color yellow is completed in the image forming unit A, the developing device is switched, and the third color cyan developing device 4c comes into contact with the photosensitive drum 1a. When the development of the second color magenta is completed in the image forming unit B, the developing device is switched, and the developing device 4d for the fourth color black comes into contact with the photosensitive drum 1b. The intermediate transfer belt 61 carrying the toner images of the first color and the second color makes one rotation and reaches the image forming unit again. However, the image forming unit A has 3 so that the toner image on the intermediate transfer belt 61 is aligned. A color cyan toner image and a fourth color black toner image are formed in the image forming portion B, and are transferred onto the intermediate transfer belt 61.

  When the two-color toner images are transferred onto the intermediate transfer belt 61, the recording material P synchronized with the movement of the intermediate transfer belt 61 is transported and separated on the intermediate transfer belt 61 during the toner image formation. The secondary transfer roller 66 has a predetermined peripheral speed difference from the intermediate transfer belt 61 and contacts the intermediate transfer belt 61 via the recording material P. The four-color toner image on the intermediate transfer belt 61 is recorded on the recording material P. It is transcribed onto the top. The recording material P onto which the four-color toner image has been transferred is melted and fixed by a conventionally known heating and pressure fixing device 8 to obtain a color image.

  Further, the untransferred toner on the photosensitive drums 1a and 1b is cleaned by cleaning devices 7a and 7b of known blade means, respectively. Further, the transfer residual toner on the intermediate transfer belt 61 is also cleaned by a cleaning device 67 such as a fur brush or a web that can be contacted and separated.

  As described above, in the 2-pass method, the intermediate transfer belt 61 requires two rotations in order to obtain a full color image, and a recording speed twice as high as that in the 4-pass method can be obtained. In addition, only two image forming units are required, and the image forming unit can be reduced to a half of the one-pass method. Therefore, it is possible to provide a smaller and lower-cost device.

JP 2002-214866 A

  However, in the above-described conventional example of the two-pass method, the following problem has occurred.

  1) Due to the contact shock of the secondary transfer roller 66 with respect to the intermediate transfer belt 61, mechanical vibration is generated at one or both of the primary transfer position T1a and the primary transfer position T1b.

  2) Further, in the conventional image forming apparatus, the peripheral speed of the secondary transfer roller 66 is set to about 100.1 to 102.0% with respect to the peripheral speed of the intermediate transfer belt 61 in order to improve transferability in the secondary transfer portion. The peripheral speed difference is attached. At this time, the moment of the peripheral speed of the intermediate transfer belt at one or both of the primary transfer position T1a and the primary transfer position T1b due to the shock that the secondary transfer roller 66 contacts the intermediate transfer belt 61. Changes occur.

  This vibration and change in peripheral speed cause transfer blur when the toner image is transferred from the photosensitive drum to the intermediate transfer belt.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus that can prevent transfer blur at the primary transfer position due to a contact shock of the secondary transfer roller. It is to provide.

  In order to achieve the above object, a typical configuration of the present invention includes a first image forming unit and a second image forming unit arranged around a moving endless image carrier, There are two switchable developing devices around at least the electrostatic latent image carrier, and the latent images formed on the electrostatic latent image carrier by exposure by the exposure device are sequentially converted into toner images by the two developing devices. And the step of transferring the toner image onto the image carrier by the first transfer means is performed in each of the two image forming units, and a plurality of toner images formed on the image carrier are transferred to the image carrier. In the image forming apparatus that performs batch transfer onto the recording material by the second transfer means that can contact and separate, the distance on the image carrier and the second image forming unit in the moving direction of the image carrier. The distance from the first transfer position to the second transfer position is Lb, and the moving direction length of the recording material When the Lm, characterized in that the relationship is Lb ≧ Lm.

  According to the present invention, it is possible to prevent the transfer blur in the first transfer unit due to the contact shock of the second transfer unit.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in the following embodiments should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. As long as there is no specific description, it is not the meaning which limits the scope of the present invention only to them.

<Embodiment 1>
1 is a cross-sectional view of a main part of an image forming apparatus according to Embodiment 1 of the present invention. Hereinafter, it demonstrates along a figure. Components having the same configurations and functions as those of the conventional example are denoted by the same reference numerals, and description thereof is omitted.

  When a four-color toner image is formed on the intermediate transfer belt 61 as an image carrier and transferred to the recording material P, a secondary transfer roller 66 as a second transfer means that can be contacted and separated is attached to the intermediate transfer belt 61. The contact timing must be before the leading edge of the toner image on the intermediate transfer belt 61 reaches the secondary transfer position T2. This is because if the front end of the toner image abuts after passing through the secondary transfer position T2, the front end of the toner image is not normally transferred onto the recording material.

  On the other hand, at the moment when the secondary transfer roller 66 comes into contact, mechanical vibration is generated, and the vibration is transferred to the photosensitive drums 1a and 1b as the electrostatic latent image carrier and the primary transfer roller as the first transfer means. As a result, the rotational torque of the intermediate transfer belt 61 changes, and the peripheral speed of the intermediate transfer belt changes instantaneously. This vibration and change in peripheral speed cause transfer blur when the toner image is transferred from the photosensitive drum to the intermediate transfer belt. This transfer blur becomes horizontal stripes on the actual image, and degrades the image quality. Even if the rigidity of the apparatus main body, the photosensitive drum, and the first transfer means is increased, it is extremely difficult to prevent transfer blur completely.

  Therefore, in the present embodiment, the distance Lb in the moving direction of the intermediate transfer belt 61 between the primary transfer position T1b and the secondary transfer position T2 of the second image forming portion B on the intermediate transfer belt 61 (hereinafter referred to as “Lb”). The above-described transfer blur is avoided by making the following relationship between the recording material conveyance direction length Lm (hereinafter referred to as the recording material length) and the recording medium length T1b-T2. .

Lb ≧ Lm (1)
By satisfying the above expression (1), the secondary transfer roller is before the toner image on the intermediate transfer belt 61 reaches the secondary transfer position T2 and after the primary transfer at the second image forming unit B. 66 can be brought into contact with the intermediate transfer belt 61. Regarding the primary transfer of the first image forming unit A, the first image forming unit A is located on the upstream side of the second image forming unit B in the moving direction of the intermediate transfer belt 61. The expression (1) is a sufficient condition earlier than the image forming unit B.

  Here, the recording material length Lm will be described.

  If the maximum recording material length that can be recorded by the apparatus satisfies the above formula (1), the recording material having a length equal to or shorter than the maximum recording material necessarily satisfies the above formula (1). Therefore, by setting the length of the maximum recording material that can be recorded by the apparatus to the recording material length Lm that satisfies the above formula (1), it is possible to cope with recording materials of all sizes. .

  In general, an image forming apparatus is designed as a recording material having a fixed size defined by a standard such as JIS or the like (hereinafter referred to as a most frequently used recording material). Specifically, for example, there are two types of A4 size (length 297 mm) and A3 size (length 420 mm). Accordingly, Lm = 297 mm in an A4 size image forming apparatus and Lm = 420 mm in an A3 size image forming apparatus, and Lb satisfying the above equation (1) may be set based on this.

  However, there is a case where a recording material longer than the most frequently used recording material is designed to be recordable. For example, it is a legal size (length 356 mm) in an A4 size compatible image forming apparatus. In this case, Lm = 356 mm may be set to correspond to the legal size. On the other hand, as Lm increases, Lb satisfying the above formula (1) increases, and this is because the circumference of the intermediate transfer belt 61 is increased. It means that it becomes large, and as a result, the whole apparatus becomes large.

  Therefore, regarding the correspondence to the recording material having a size larger than the recording material length Lm satisfying the above formula (1), the contact of the secondary transfer roller 66 is performed and the intermediate transfer belt 61 is further rotated once, that is, Transfer blurring may be avoided by performing after the trailing edge of the four-color toner image has passed the secondary transfer position T2. In this way, even when continuous recording is performed with a recording material that does not satisfy the above formula (1), the rotation of the intermediate transfer belt 61 required for recording per sheet can be suppressed to 3 rotations. An increase in the size of the apparatus can be prevented while suppressing an increase in recording time.

  As described above, according to the present embodiment, the relationship between the T1b-T2 distance Lb and the recording material length Lm satisfies Lb ≧ Lm, so that the secondary transfer roller does not decrease the recording speed. The transfer blur at the primary transfer position T1b of the second image forming portion B due to the contact shock 66 can be prevented.

<Embodiment 2>
FIG. 2 is a cross-sectional view of the main part of the image forming apparatus according to the embodiment of the present invention. Components having the same configurations and functions as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The present embodiment relates to a method for avoiding transfer blur in the first image forming portion A due to a contact shock of the secondary transfer roller 66. The transfer blur of the first image forming unit A occurs after the second sheet when a plurality of prints are continuously performed. That is, the contact shock of the secondary transfer roller 66 when performing the secondary transfer process for the first sheet causes the transfer blur of the first sheet of the second sheet performed in the first image forming unit A. In particular, this embodiment is effective when the intermediate transfer belt 61 is provided with a plurality of image leading edge detection members in order to improve the printing speed.

  In order to avoid the transfer blur described above, the first transfer process for the first color of the second sheet may be started after the secondary transfer roller 66 comes into contact. Therefore, in the present embodiment, the movement of the intermediate transfer belt 61 from the primary transfer position T1a of the first image forming unit A on the intermediate transfer belt 61 to the primary transfer position T1b of the second image forming unit A is performed. Distance Lab in the direction (hereinafter referred to as the distance between T1a and T1b), the distance Lb between T1b and T2 in the second image forming unit B, and the second image leading edge detection unit Lt2 and the first image leading edge detection. The above-described transfer blur is achieved by setting the distance Lt12 (hereinafter referred to as Lt2-Lt1 distance) in the moving direction of the intermediate transfer belt 61 to the portion Lt1 and the recording material length Lm as follows. It is avoiding.

Lab + Lm ≦ Lt12 (2)
FIG. 2 shows the moment when the secondary transfer roller 66 for performing the secondary transfer of the first sheet comes into contact with the intermediate transfer belt 61. In the figure, I indicated by a thick dotted line on the intermediate transfer belt 61 is the intermediate transfer belt. This is the first toner image on the belt 61, and the leading edge position of the toner image I1 is It1, which is an image leading edge detection unit on the intermediate transfer belt 61. I2 indicated by a thick dotted line on the photosensitive drum 1a of the first image forming section B is the first color toner of the second sheet, and the tip of the toner image I2 is an image on the intermediate transfer belt 61 at a predetermined timing. Primary transfer is performed on the tip detection unit It2. Here, the distance from the position It1 to the secondary transfer position T2 is Li, and the distance from the It2 on the intermediate transfer belt 61 on the upstream side as viewed from It1 is It12 (see FIG. 3).

  As described in the above-described embodiment, the distances Lb and Lm satisfy the expression (1) in order to prevent transfer blur at the first transfer unit in the second image forming unit, and the secondary transfer roller 66. The contact with the intermediate transfer belt 61 is before the image leading edge It1 reaches the secondary transfer position T2 and after the primary transfer of the fourth color is completed. Therefore, the above-mentioned distance Li is as follows.

0 ≦ Li ≦ Lb−Lm (3)
Next, the primary transfer of the first color of the second sheet will be described.

  Regarding the second toner image, the leading edge of the image on the intermediate transfer belt 61 is the position It2. As described above, in order to avoid the contact shock of the secondary transfer roller 66 in the first image forming section A, the primary transfer may be started after the secondary transfer roller 66 is contacted. is there. In this case, it is necessary that Lb + Lab ≦ Lt12. That is, from Expression (3), Lab + Lm ≦ Lt12 (Expression (2)).

  Particularly in the formula (2), when Lab + Lm = Lt12, the second image leading edge It2 is maintained while maintaining the conditions for starting the first transfer of the first color of the second sheet after the secondary transfer roller 66 comes into contact. Can be on the most upstream side in the rotation direction of the intermediate transfer belt 61. In this case, during continuous recording, the printing speed can be increased in continuous printing of two or more sheets by shifting the Itop position by a predetermined amount in the upstream direction of the intermediate transfer belt 61 for each number of recording sheets.

  In an actual apparatus, it may be designed to satisfy the formulas (1) and (2) in consideration of variations in time required for the secondary transfer roller 66 to contact. Also in this embodiment, the length Lm of the recording material may be the maximum recording material length that can be recorded by the apparatus, or the length of the most frequently used recording material.

  As described above, according to the present embodiment, in addition to the first embodiment described above, the relationship between the distance Lab between T1a and T1b, the distance between Lt2 and Lt1 Lt12, and the recording material length Lm is expressed as Lab + Lm ≦ By setting Lt12, in addition to the effects of the first embodiment, the transfer blur of the first image forming portion due to the contact shock of the secondary transfer roller 66 in the second and subsequent sheets can be prevented without reducing the recording speed. can do.

  In the above-described embodiment, the printer is exemplified as the image forming apparatus. However, the present invention is not limited to this, and other image forming apparatuses such as a copying machine and a facsimile apparatus, or their functions are used. Another image forming apparatus such as a combined machine may be used, and the same effect can be obtained by applying the present invention to the image forming apparatus.

1 is a cross-sectional view of a main part of an image forming apparatus according to Embodiment 1 of the present invention. It is sectional drawing of the image forming apparatus principal part which concerns on Embodiment 2 of this invention. It is a detailed explanatory view of an image forming apparatus according to Embodiment 2 of the present invention. It is an explanatory diagram of a conventional 4-pass image forming apparatus. It is an explanatory view of a conventional one-pass image forming apparatus. It is an explanatory diagram of a conventional two-pass image forming apparatus.

Explanation of symbols

A, B Image forming section P Recording material T1a, T1b Primary transfer position T2 Secondary transfer position 1a, 1b Photosensitive drum (electrostatic latent image carrier)
2a, 2b Charging roller 3a, 3b Exposure device 4a, 4b, 4c, 4d Developing device 7 Cleaning device 8 Fixing device 61 Intermediate transfer belt (image carrier)
62 driving roller 63 driven roller 64 tension roller 65a, 65b primary transfer roller (first transfer means)
66 Secondary transfer roller (second transfer means)
67 Cleaning device

Claims (4)

A first image forming unit and a second image forming unit are arranged around an endless image carrier that moves, and each of the image forming units has two developments that can be switched at least around the electrostatic latent image carrier. A latent image formed on the electrostatic latent image carrier by exposure by an exposure device is sequentially converted into a toner image by the two developing devices, and the toner image is formed on the image carrier by a first transfer unit. And transferring the toner images formed on the image carrier onto the recording material by a second transfer means capable of coming into contact with and separating from the image carrier. In the image forming apparatus for batch transfer to
The distance on the image carrier, which is the distance from the first transfer position to the second transfer position of the second image forming unit in the moving direction of the image carrier, is Lb, and the moving direction length of the recording material is An image forming apparatus characterized in that when Lm, the relationship is Lb ≧ Lm. The distance on the image carrier during continuous image formation, and the distance from the second image leading edge position to the first image leading edge position in the moving direction on the image carrier is Lt12. A distance on the carrier, and a distance from the first transfer position of the first image forming unit to the first transfer position of the second image forming unit in the moving direction on the image carrier as Lab, When the moving direction length of L is Lm,
Lab + Lm ≦ Lt12
The image forming apparatus according to claim 1, wherein:   3. The image forming apparatus according to claim 1, wherein the length Lm of the transfer material is a length of the longest transfer material corresponding to the image forming apparatus.   3. The image forming apparatus according to claim 1, wherein the length Lm of the transfer material is a length of the most frequently used transfer material in the image forming apparatus.

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