JP2008090092A - Image forming apparatus - Google Patents

Abstract

An object of the present invention is to record an image transferred from a photosensitive drum to a recording material via an intermediate transfer belt without using a special part or mechanism, and to record from the photosensitive drum without using an intermediate transfer belt. This is to accurately align the image directly transferred to the material.
A secondary transfer position P2 for transferring an image transferred from a photosensitive drum 2C, 2Y, 2M to an intermediate transfer belt 11 at a primary transfer position onto a recording material, and a conveying direction of the recording material from the secondary transfer position P2. The image transferred at the primary transfer position P1M is directly transferred in the image forming apparatus in which the direct transfer position PB for directly transferring the image from the photosensitive drum 2B to the recording material on the downstream side is arranged in the transport path of the recording material T / t is an integer, where T is a time required to reach the position PB and t is a rotation period of the driving roller 12 that rotationally drives the intermediate transfer belt 11.
[Selection] Figure 1

Description

  The present invention relates to an image forming apparatus capable of forming a color image on a recording material using a plurality of image forming units provided for each color.

  Conventionally, as a color image forming apparatus having a plurality of image forming units, a color image forming apparatus in which two different transfer points are arranged in parallel on a recording material has been proposed (Japanese Patent Laid-Open No. 2004-205943). ). In order to shorten the initial printout time during monochrome printing, this transfer point is used for direct transfer of the black image forming portion at one place, and for the other color image forming portion using the intermediate transfer method at the other place. Secondary transfer is used.

  Specifically, this color image forming apparatus has a secondary transfer portion of the intermediate transfer belt on which the color image is formed in the transfer portion upstream in the conveyance direction of the recording material, and forms a black image in the downstream transfer portion. It has a direct transfer part. The four color image forming units are arranged in such a manner that three color image forming units having different colors are arranged in parallel above the intermediate transfer belt, and a black image forming unit is arranged above the color image forming unit. According to this configuration, at the time of monochrome printing, it is possible to directly transfer to the recording material without being transferred to the intermediate transfer belt, and compared to the case of direct transfer to the recording material by the direct transfer method of the four-color inline configuration, The initial printout time can be shortened.

  Further, as described above, in the color image forming apparatus, the image transfer position from the black image forming unit (direct transfer unit) and the image transfer position from the other color image forming unit (secondary transfer unit) are transported of the recording material. Side by side. For this reason, the recording material fed to the transport path from one feeding cassette is transported to both the direct transfer position by the black image forming unit and the secondary transfer position through the intermediate transfer belt from the other color image forming unit. can do.

JP 2004-205943 A

  In the image forming apparatus using the intermediate transfer method, the interval between the plurality of image forming units arranged side by side on the intermediate transfer belt is related to the circumferential length of the driving roller that stretches and rotates the intermediate transfer belt. In many cases, the interval between the image forming portions is an integral multiple of the circumferential length of the drive roller. This is for canceling the speed fluctuation of the drive roller period that causes the rotational speed fluctuation of the intermediate transfer belt. With this configuration, even if there is speed variation in the driving roller cycle, the images of each color by the plurality of image forming units are superimposed at the same position on the intermediate transfer belt without color misregistration.

  However, in the above conventional example, when forming a color image using four colors, after superimposing the three color images on the intermediate transfer belt, the image is transferred to the recording material at the secondary transfer position, and further, The black image is superimposed on the color image on the recording material at the downstream direct transfer position. For this reason, when there is a speed variation in the driving roller cycle of the intermediate transfer belt, there is a possibility that a positional shift (color shift) may occur when the black image is superimposed on the three color images on the recording material.

  In order to avoid this problem, for example, there is means for creating process black by mixing three colors of cyan, yellow, and magenta without superimposing the three colors and black. However, when creating black text, since three colors are superimposed on one character, there is a possibility that toner scatters more than when only one color (black) is used. Further, since the gloss value is higher in the portion where the three colors are superimposed than in the case of only one color, the reflection of the light of the black text by the three colors is strong, and in some cases it is difficult to read. In the case of creating black halftone image data, the color halftone becomes conspicuous even with a slight color shift, and the black halftone image stability becomes a problem. For this reason, the three colors must be stably and accurately superimposed, but it is difficult to ensure the positional accuracy that satisfies this required performance. From the above, it can be seen that it is preferable to use black toner in the black portion of the image rather than process black by superimposing three colors.

  Accordingly, an object of the present invention is to provide an image transferred from the image carrier to the recording material via the intermediate transfer member without using special parts or mechanisms, and from the image carrier to the recording material without passing through the intermediate transfer member. Is to accurately align the image directly transferred to the image.

  A typical configuration of the present invention for achieving the above object is a second transfer position for transferring an image transferred from the first image carrier to the intermediate transfer body at the first transfer position onto a recording material, Image formation in which the third transfer position for directly transferring the image from the second image carrier to the recording material on the downstream side in the recording material conveyance direction from the second transfer position is arranged in parallel with the recording material conveyance path. In the apparatus, when T is a time required for the image transferred at the first transfer position to reach the third transfer position, and t is a rotation period of the rotating body that rotationally drives the intermediate transfer body, T / t is an integer.

  According to the present invention, the image transferred from the first image carrier to the recording material via the intermediate transfer member without using any special parts or mechanism, and the recording material on the downstream side in the conveyance direction of the recording material. The image directly transferred from the second image carrier to the recording material can be accurately aligned. It is possible to minimize the displacement of the transferred image due to the uneven rotational speed of the rotating body that rotates the intermediate transfer body.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be changed as appropriate according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless specifically stated otherwise, the scope of the present invention is not intended to be limited thereto.

  A schematic configuration of the image forming apparatus will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a color image forming apparatus. As shown in FIG. 1, the image forming apparatus includes four color image forming portions 1C, 1Y, 1M, and 1B of cyan, yellow, magenta, and black. Each color image forming unit includes photosensitive drums 2C, 2Y, 2M, and 2B as image carriers, and sequentially surrounds the vicinity of the peripheral surface, and charging devices 3C, 3Y, 3M, and 3B, and developing devices 4C and 4C, respectively. 4Y, 4M, and 4B are arranged. In addition, blades 8C, 8Y, 8M, and 8B for cleaning residual toner on each photosensitive drum are provided. In each image forming unit, the photosensitive drum, the charger, the developing device, and the blade are integrated as a process cartridge that can be attached to and detached from the image forming apparatus main body. A predetermined interval is provided between the charger and the developing device, and exposure irradiation is performed on the peripheral surface of the photosensitive drum from the scanner device 10 as an exposure unit through this gap. The image forming apparatus also includes an intermediate transfer belt 11 as an intermediate transfer member, a driving roller 12 and a driven roller 13 that stretch the intermediate transfer belt 11, a feeding cassette 14, a feeding roller 15, a registration roller 16, and a fixing roller. 17, discharge rollers 18, 19 and the like are disposed.

  The image forming portions 1C, 1Y, 1M, and 1B are arranged in a substantially straight line, and an intermediate transfer belt 11 is disposed below the image forming portions 1C, 1Y, 1M, and 1B. The intermediate transfer belt 11 is pressed against the photosensitive drums 2C, 2Y, and 2M other than the photosensitive drum 2B by the primary transfer rollers 5C, 5Y, and 5M, and is rotated clockwise by a driving roller 12 as a rotating body that is rotationally driven by a driving motor. Rotate. Each primary transfer roller and the photosensitive drum constitute a primary transfer portion via the intermediate transfer belt 11. The drive roller 12 is disposed in the recording material conveyance path, and a secondary transfer roller 6 as a transfer member is provided at a position facing the drive roller 12. The secondary transfer roller 6 and the driving roller 12 constitute a secondary transfer portion via the intermediate transfer belt 11. An image forming unit 1B is disposed downstream of the secondary transfer unit in the recording material conveyance direction, and the black photosensitive drum 2B is disposed in the recording material conveyance path. A black transfer roller 7 for directly transferring an image from the drum 2B to a recording material is disposed at a position facing the black photosensitive drum 2B. The black photosensitive drum 2B and the black transfer roller 7 directly constitute a transfer portion.

  A color image forming operation in this image forming apparatus will be described below. The surface of each photosensitive drum that is driven to rotate is uniformly charged by each charger. Then, the image forming signal is transmitted to the image forming apparatus via various networks and the like, and the scanner device 10 irradiates each photosensitive drum with laser light corresponding to each place based on the image forming signal. In this way, each developing device develops the electrostatic latent image formed by the potential difference formed on the photosensitive drum with each color toner, and visualizes it.

  Each color toner image formed on the surface of each color photosensitive drum 2C, 2Y, 2M as the first image carrier is caused by the action of an electric field at a position facing each primary transfer roller 5C, 5Y, 5M. Primary transfer is performed on the intermediate transfer belt 11 that is electrostatically rotated. At this time, first, a cyan toner image is primarily transferred to the intermediate transfer belt 11 at a primary transfer position facing the primary transfer roller 5C. Subsequently, a yellow toner image is primarily transferred onto the intermediate transfer belt 11 on the intermediate transfer belt 11 at a primary transfer position facing the primary transfer roller 5Y. Further, magenta toner images are similarly superimposed at the primary transfer position (first transfer position) P1M facing the primary transfer roller 5M, and a three-color toner image is formed on the intermediate transfer belt 11.

  The three color toner images are conveyed to the secondary transfer position (second transfer position) P2 where the driving roller 12 and the secondary transfer roller 6 face each other as the intermediate transfer belt 11 rotates. On the other hand, one sheet of recording material stored in the feeding cassette 14 is conveyed to the secondary transfer position P <b> 2 through the feeding roller 15 and the registration roller 16. Then, the toner image and the recording material on the intermediate transfer belt 11 reach the secondary transfer position P2 at the same time, and the toner image becomes electrostatic by the action of the transfer electric field generated by the intermediate transfer belt 11 and the secondary transfer roller 6. Is transferred to a recording material.

  The recording material onto which the three color toner images have been transferred is conveyed to the black image forming unit 1B by the conveying force obtained by the driving roller 12 and the secondary transfer roller 6. The toner image formed on the surface of the black photosensitive drum 2B as the second image carrier is transferred onto the recording material conveyed at the black transfer position (third transfer position) PB opposed to the black transfer roller 7. A full color image is formed by superimposing on the color toner image.

  The recording material that holds the full-color toner image on the surface passes through the nip portion of the fixing roller 17. At that time, the full-color toner image is melted by the action of heat and pressure and fixed on the recording material as a permanent image, and the image formation is completed.

  Next, a monochrome image forming operation will be described. During monochrome image formation, toner image formation by the color image forming portions 1C, 1Y, 1M, primary transfer to the intermediate transfer belt 11, and secondary to the recording material at the nip portion between the intermediate transfer belt 11 and the secondary transfer roller 6 There is no transcription. Further, the secondary transfer roller 6 has a mechanism that is separated from the intermediate transfer belt 11, and is separated from the intermediate transfer belt 11 when a monochrome image is formed. At the time of monochrome image formation, first, the recording material on which the toner image has not been transferred is conveyed from the feeding cassette 14 to the black image forming unit 1B. When the recording material is conveyed to the nip between the black photosensitive drum 2B and the black transfer roller 7, the black toner image is transferred to the recording material at the nip portion. Then, the recording material after the transfer of the black toner image is conveyed to the fixing roller 17 and the toner image is fixed. As a result, a monochrome image containing only the black component is formed on the recording material. The recording material that has passed through the fixing roller 17 is discharged to a discharge portion at the upper part of the apparatus by a discharge roller 19. Further, during this series of monochrome image formation, the intermediate transfer belt 11 and the color image forming units 1C, 1Y, 1M are not driven and are in a stopped state.

  According to the image forming apparatus, there are only two toner image transfer points in the recording material conveyance path, and the length of the recording material conveyance path from the feeding cassette 14 to the discharge portion downstream of the fixing roller 17 is set to the conventional color. Compared with the direct transfer method in the image forming apparatus, it can be shortened. As a result, it is possible to transport the recording material from the feeding cassette 14 to the black image forming unit without passing through a color image forming unit that is not necessary for the image formation at the time of black image formation. Can be shortened.

  In addition, when performing monochrome printing by the indirect transfer method in the conventional color image forming apparatus, it is necessary to primarily transfer the toner image formed in the black image forming unit to the intermediate transfer belt and then to the secondary transfer to the recording material. is there. Therefore, according to the image forming apparatus, it is possible to shorten the time compared to the indirect transfer method in which the printout time is increased by the time for performing the transfer twice. Further, during monochrome printing, the color image forming units 1C, 1Y, 1M and the intermediate transfer belt 11 do not rotate, so that the life of the intermediate transfer belt 11 and the color image forming units 1C, 1Y, 1M can be extended.

  Next, the relationship between the time required for the image transferred at the primary transfer position P1M to reach the direct transfer position PB and the rotation period of the driving roller 12 of the intermediate transfer belt 11 will be described.

  In color image formation, the required performance with respect to a positional deviation amount (color deviation amount) between a plurality of toner images to be superimposed is high. Here, since the black image forming unit 1B does not superimpose the toner image on the same intermediate transfer belt 11, there is a possibility that color misregistration occurs between the three colors of cyan, yellow, and magenta and black. To solve this problem, there is a means for forming a black image by forming process black by superimposing three colors of cyan, yellow, and magenta, and forming an image. However, when creating a text image, if three colors are superimposed, toner scattering may increase, and it is difficult to maintain print quality. Even when a black halftone is formed with a photographic image or the like, if a halftone is formed with process black, cyan, yellow, and magenta colors are easily visible, and it is difficult to stably print a gray image. Therefore, in order to create an image by effectively using black in addition to cyan, yellow, and magenta, a technique for superimposing the four colors is important.

  Therefore, in the present image forming apparatus, the following relationship exists between the time T required for the image transferred at the primary transfer position of the color image forming unit to reach the direct transfer position of the black image forming unit and the rotation period t of the driving roller 12. Is given. Here, the required time T from the primary transfer position P1M of the magenta 1M on the most downstream side of the color image forming unit to the direct transfer position PB of the black 1B via the secondary transfer position P2 rotates the intermediate transfer belt 11. The driving roller 12 is made to be an integer of the period t of one rotation. That is, the value of T / t is an integer.

  Here, the operation and effect of the case where the value of T / t is an integer will be described by taking as an example the case of forming equally spaced lines of four colors. The intermediate transfer belt 11 repeats rotation unevenness with a cycle of one rotation due to eccentricity of the drive roller 12 or the like. Due to the belt speed unevenness caused by the rotational unevenness, the image is transferred with a wide line pitch when it is fast and with a narrow line pitch when it is slow. In order not to make the color misregistration between the colors caused by the rotation unevenness, the required time between the cyan, yellow, and magenta image forming units is made equal to one rotation period t of the drive roller 12. That is, the time required for the image transferred at the previous first transfer position to reach the next first transfer position is equal to one rotation period t of the drive roller 12. As a result, the toner images of the three colors cyan, yellow, and magenta are located on the intermediate transfer belt at positions different from the ideal positions (equal intervals), but there is no relative position error of the toner images between the colors. Can be made. A portion transferred at a low speed has a narrow line pitch for cyan, yellow, magenta, and three colors, and a portion transferred at a high speed has a wide line pitch for cyan, yellow, magenta, and three colors (FIG. 2). reference).

  Further, as described above, the required time between the primary transfer positions of the image forming units 1C, 1Y, 1M is equal to one rotation period of the driving roller 12. For this reason, the primary transfer position of the color image forming unit serving as the base point of the required time T to the direct transfer position described above is not limited to the primary transfer position of the magenta image forming unit 1M, and the cyan image forming unit 1C or the yellow image forming unit. It may be the primary transfer position of the portion 1Y. Even in this case, the value of T / t is an integer.

  The three color toner images superimposed on the intermediate transfer belt 11 are secondarily transferred onto the recording material fed from the feeding cassette at the secondary transfer position P2, and the line pitch of each color is intermediate. The image is transferred at the same position as the image on the transfer belt 11. This is because the conveyance speed of the recording material is equal to the speed of the intermediate transfer belt 11. The recording material sent from the feeding cassette 14 to the secondary transfer position P <b> 2 is immediately separated from the upstream conveying roller 16, so that the conveyance is performed via the intermediate transfer belt 11 and the driving roller 12 and the secondary transfer roller. 6 is performed. As a result, the recording material is fed to the black direct transfer position PB while having the same speed fluctuation in one rotation cycle of the drive roller 12 as the intermediate transfer belt 11. Here, as described above, the required time T from the transfer position P1M of magenta 1M to the transfer position PB of black 1B is set to an integral multiple (here, 7 times) of one rotation period t of the drive roller 12. As a result, the recording material is sent slowly when an image with a narrow line pitch reaches black, and the recording material is sent fast when an image with a wide line pitch reaches black. Therefore, since the narrow and wide line pitch of black can be synchronized with the narrow and wide line pitch of the three colors, no color shift (position shift) occurs.

  The following is a description from the moving speed of the toner image. FIG. 3 shows what speed fluctuation occurs while the toner image formed on the first image carrier is conveyed with the intermediate transfer belt 11 and the recording material. The toner image is conveyed on the intermediate transfer belt 11 and the recording material at the rotational speed of the driving roller 12 that determines the moving speed of the intermediate transfer belt 11 and the conveying speed of the recording material. The speed fluctuates with the rotation cycle.

  For example, it is assumed that a toner image is transferred onto the intermediate transfer belt 11 by the first image forming unit (cyan) when the intermediate transfer belt 11 rotates most slowly. When the toner image reaches the next second image forming unit (yellow), the toner image is in the slow state as when it was transferred by the first image forming unit. Similarly, when the third image forming unit (magenta) is reached, the state becomes the slowest. Then, when passing through the secondary transfer position P2 and reaching the transfer position PB of the fourth image forming portion (black), the required time T from the last primary transfer position P1M to the transfer position PB is the driving roller 12 It is in the relationship (T / t) of the integral multiple of one rotation time t. Therefore, the toner image superimposed and transferred on the recording material at the secondary transfer position P2 is the same as that at the third image forming portion (magenta) at the direct transfer position PB downstream from the secondary transfer position P2. Reach at the slowest speed.

  As a result, the toner image at a certain position can be kept at the same speed during primary transfer and direct transfer on the intermediate transfer belt 11 and the recording material. When the line pitch is written, the relationship between the narrow and wide pitch can be maintained.

  By adopting these configurations, it is possible to reduce color misregistration between a three-color image formed by the indirect transfer method and a black image by the direct transfer method.

  In this embodiment, the peripheral speeds of the photosensitive drum 2, the intermediate transfer belt 11, and the recording material are substantially constant. For this reason, the required time T from magenta 1M to black 1B is an integral multiple of one rotation period t of drive roller 12, and at the same time, the distance from transfer position P1M of magenta 1M to transfer position PB of black 1B 12 is an integral multiple of one rotation distance (circumferential length).

  Here, the integer range of T / t described above will be described in detail. The integer should ideally be a true integer, but may have a slight width depending on the product configuration, and can be paraphrased as an almost integer. Here, the positional shift of each color generated by one rotation of the driving roller has a periodic fluctuation of a substantially sine waveform, and the amplitude thereof is about ± 50 μm. In this case, the deviation from an integer to 0.01 (for example, T / t = 7.01) is 3.6 degrees when converted into a phase difference of a sine waveform, and the positional deviation is 3.1 μm. The deviation from the integer to 0.1 (for example, T / t = 7.1) is a phase deviation of 36 degrees and a positional deviation of 29.4 μm. Further, the belt thickness variation in the circumferential direction that always occurs during processing becomes a speed variation of one rotation of the belt, which causes a positional shift. Since the permissible value is 30 μm, the permissible value of the displacement of the AC component caused by the phase difference can be about the same. Judging from the above-described allowable deviation in position caused by the belt film pressure unevenness, the level of the difference from the integer ratio of 0.01 is within the allowable range without any problem, and the difference from the integer ratio is 0.1. The level is the upper limit of the allowable value. Therefore, a phase difference greater than this is an unacceptable numerical value. This allowable value has a range depending on the main body configuration and required performance (positional deviation, color misregistration allowable value, etc.), and the value of T / t described above is in the range of integer value ± 0.1.

  As described above, by setting T / t to be an integer, an image transferred to a recording material via an intermediate transfer belt can be recorded without using a special part or mechanism, and a recording can be performed without using an intermediate transfer belt. It is possible to accurately align the image directly transferred to the material. It is possible to minimize the displacement of the transferred image due to uneven rotation speed of the driving roller that rotationally drives the intermediate transfer belt. Thereby, a higher quality color image is obtained.

  In the above-described embodiment, the configuration in which the number of image forming units provided in parallel on the intermediate transfer belt is three is illustrated. However, the number of use is not limited, and may be appropriately set as necessary. good.

  In the above-described embodiment, as a process cartridge that is detachable from the main body of the image forming apparatus, a process that integrally includes a photosensitive drum and a charging unit, a developing unit, and a cleaning unit as a process unit that acts on the photosensitive drum. A cartridge was illustrated. However, the present invention is not limited to this. For example, in addition to the photosensitive drum, a process cartridge that integrally includes any one of a charging unit, a developing unit, and a cleaning unit may be used.

  Further, in the above-described embodiment, the configuration in which the process cartridge including the photosensitive drum is detachable from the main body of the image forming apparatus is exemplified, but the present invention is not limited to this. For example, an image forming apparatus in which each constituent member is incorporated, or an image forming apparatus in which each constituent member is detachable may be used.

  In the above-described embodiments, 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 machine, or a combination of these functions. Other image forming apparatuses such as multifunction peripherals may also be used. The same effect can be obtained by applying the present invention to these image forming apparatuses.

Schematic cross-sectional view showing schematic configuration of image forming apparatus Plan view showing line images of each color with no relative displacement The figure which shows the moving speed nonuniformity of a certain toner image, and the passage position of each image formation part

Explanation of symbols

P1M ... primary transfer position P2 ... secondary transfer position PB ... direct transfer positions 1C, 1Y, 1M, 1B ... image forming unit 2B ... photosensitive drum (second image carrier)
2C, 2Y, 2M ... photosensitive drum (first image carrier)
5C, 5Y, 5M ... primary transfer roller 6 ... secondary transfer roller (transfer member)
7: Transfer roller 11: Intermediate transfer belt (intermediate transfer member)
12 ... Driving roller (rotating body)

Claims (4)

A second transfer position for transferring an image transferred from the first image carrier to the intermediate transfer member at the first transfer position onto the recording material; and a downstream side in the conveying direction of the recording material from the second transfer position. In the image forming apparatus in which the third transfer position for directly transferring the image from the second image carrier to the recording material is arranged in parallel with the conveyance path of the recording material,
Assuming that the time required for the image transferred at the first transfer position to reach the third transfer position is T, and t is the rotation period of the rotating body that rotationally drives the intermediate transfer body, T / t Is an integer.   2. The image forming apparatus according to claim 1, wherein the T / t is an integer, wherein the value of the T / t is within a range of an integer ± 0.1.   The recording material fed to the second transfer position is conveyed at a constant speed with the intermediate transfer member by a nip formed by the intermediate transfer member and a transfer member facing the intermediate transfer member. The image forming apparatus according to claim 1 or 2.   The intermediate transfer member is provided with a plurality of the first image carriers, and the time required for the image transferred at the first transfer position to reach the next first transfer position is 4. The image forming apparatus according to claim 1, wherein the image forming apparatus is equal to one rotation period of a rotating body that rotationally drives the intermediate transfer body. 5.

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