JP2011043629A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of performing image correction while continuously performing image formation. <P>SOLUTION: The image forming apparatus is configured to transfer images on image carriers 1Y, 1C and 1M being some of a plurality of image carriers 1Y, 1C, 1M and 1Bk to a recording medium on a conveyance body 14 through an intermediate transfer body 8, and transfer an image on the other image carrier 1Bk to the recording medium on the conveyance body 14 without through the intermediate transfer body 8. The image forming apparatus includes a pattern image forming means configured to form a pattern image for image correction on the respective image carriers 1Y, 1C, 1M and 1Bk, and a pattern image detection means 32 configured to detect the pattern image on the conveyance body 14. When continuously performing image formation by a plurality of number of times, the pattern images formed on the respective image carriers 1Y, 1C, 1M and 1Bk are transferred to intervals between recording medium carrying areas to carry the recording medium on the conveyance body 14. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine of these.

  In color image forming apparatuses such as copiers, printers, facsimiles, and multifunction machines of these, measures to prevent deterioration of consumables by preventing the image forming apparatus for color image formation from being driven during monochrome image formation. Has been adopted. For example, Japanese Patent Application Laid-Open No. 2006-201743 discloses an image forming apparatus that can drive a black image forming unit without driving a color image forming unit.

  As shown in FIG. 10, the image forming apparatus described in the above-mentioned Patent Document 1 transfers images of yellow, magenta, and cyan color image forming units 100Y, 100M, and 100C, and a black image forming unit 100Bk. An intermediate transfer belt 200, a paper feed cassette 300 containing recording paper P, a transport belt 400 for transporting the recording paper, a fixing device 500 for fixing an image on the recording paper, and the like. The color image forming units 100Y, 100M, and 100C are disposed on the intermediate transfer belt 200. On the other hand, the black image forming unit 100 </ b> Bk is disposed on the transport belt 400.

A full-color image forming operation in the image forming apparatus will be described with reference to FIG.
Images are formed in the image forming units 100Y, 100M, 100C, and 100Bk, respectively. Among the formed color images, the yellow, magenta, and cyan color images are displayed at the primary transfer position N1 where the color image forming units 100Y, 100M, and 100C contact the intermediate transfer belt 200, respectively. 100M and 100C are sequentially superimposed and transferred onto the intermediate transfer belt 200. The color image transferred to the intermediate transfer belt 200 is transferred to the recording paper P sent out from the paper feed cassette 300 at the secondary transfer position N2 where the intermediate transfer belt 200 and the transport belt 400 are in contact with each other. Thereafter, the formed black image is transferred from the black image forming unit 100Bk to the recording paper P on the conveying belt 400 at the direct transfer position N3 where the black image forming unit 100Bk and the conveying belt 400 are in contact with each other. . The recording paper P onto which the full color image has been transferred in this manner is sent to the fixing device 500 where the image is fixed on the recording paper P.

  When monochrome image formation is performed, the color image forming units 100Y, 100M, and 100C are not driven, and only the black image forming unit 100Bk is driven. The image formed on the black image forming unit 100Bk is directly transferred to the recording paper P at the transfer position N3, and then the image is fixed by the fixing device 500. In this way, when performing monochrome image formation, a sharp image can be obtained by directly transferring a black image onto a recording sheet, and a consumable for color image formation without driving a color image formation unit. Prevention of deterioration and reduction of scattered toner.

  In the configuration in which the color image and the black image are transferred at different positions (secondary transfer position and direct transfer position) as in the image forming apparatus described in Patent Document 1, a position between the images transferred on the recording paper is set. Misalignment is likely to occur. For this reason, a pattern image for detecting image misalignment is formed on the conveyor belt, the pattern image is detected by an optical sensor, and the image forming condition is corrected based on the detection result so as to suppress the image misalignment. It is possible. It is also conceivable to correct the image density by forming a pattern image for detecting the image density on the conveyor belt and detecting this pattern image.

  In addition, when a large amount of printing is continuously performed, it is preferable to perform image correction during printing because there is a possibility that image displacement or density change may occur during printing. However, in order to perform image correction while continuing printing, the pattern image must be transferred so as not to overlap the recording paper on the conveyance belt. If the image forming operation is temporarily stopped and the image correction is performed, and then the image forming operation is restarted, it is easy to transfer the pattern image so as not to overlap the recording paper on the conveyance belt. In this case, there is a problem that the waiting time of the user is increased and inconvenience is caused.

  In view of such circumstances, an object of the present invention is to provide an image forming apparatus capable of performing image correction while continuously performing image formation.

  The invention of claim 1 comprises a plurality of image carriers that carry an image on the surface, a carrier that carries and conveys a recording medium, and an intermediate transfer member to which an image on the image carrier is transferred, Among the plurality of image carriers, some of the images on the image carrier are transferred to the recording medium on the carrier via the intermediate transfer member, and the other images on the image carrier are In an image forming apparatus configured to be transferred to a recording medium on the conveyance body without passing through an intermediate transfer body, pattern image forming means for forming a pattern image for image correction on each image carrier; A pattern image detecting means for detecting the pattern image on the carrier, and when performing image formation a plurality of times, between the recording medium carrying regions carrying the recording medium on the carrier, Transfer of the pattern image formed on each image carrier It is those that you configured.

  When image formation is performed a plurality of times, the pattern image can be transferred between the recording medium holding areas on the conveyance body, so that the recording medium is continuously conveyed by the conveyance body while the pattern on the conveyance body is transferred. Image transfer can be performed. Thereby, it is possible to perform image correction by detecting the pattern image on the carrier without stopping the image forming operation.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the recording medium is a rotating body that conveys the recording medium while the conveying body rotates, and the recording medium having the same conveying direction length is predetermined by the conveying body. When transported continuously at intervals, control is performed so that the same area on the transport body becomes the recording medium carrying area for each cycle of rotation of the transport body.

  By controlling so that the same area on the conveyance body becomes a recording medium carrying area for each cycle of rotation of the conveyance body, it is possible to avoid the transfer of the pattern image to the recording medium. It is possible to prevent the pattern image from being stained. In addition, since the pattern image can be reliably transferred onto the carrier, the reliability of image correction is improved.

  According to a third aspect of the present invention, in the image forming apparatus according to the second aspect of the present invention, there is provided a position detecting means for detecting a position in the rotational direction of the surface of the transport body.

  By detecting the position of the surface of the conveyance body in the rotation direction by the position detection means, the accuracy of position control of the recording medium carrying area on the conveyance body is improved.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, an intermediate transfer body cleaning unit that cleans the surface of the intermediate transfer body is provided, and the pattern image on the transport body is provided. Is detected by the pattern image detecting means, and then the pattern image on the carrier is transferred to the intermediate transfer body and cleaned by the intermediate transfer body cleaning means.

  By transferring the pattern image on the carrier to the intermediate transfer member and cleaning the pattern image transferred to the intermediate transfer belt by the intermediate transfer member cleaning means, a dedicated cleaning means for cleaning the surface of the carrier is provided. There is no need to provide it, and the apparatus can be downsized.

  According to a fifth aspect of the present invention, there is provided the image forming apparatus according to any one of the first to fourth aspects, wherein the surface of the image carrier that transfers an image without passing through the intermediate transfer body is cleaned. After the pattern image on the conveyance body is detected by the pattern image detection means, the pattern image on the conveyance body is transferred to the image carrier that transfers the image without passing through the intermediate transfer body. Thus, the cleaning is performed by the image carrier cleaning means.

  By transferring the pattern image on the carrier to the image carrier and cleaning the pattern image transferred to the image carrier by the image carrier cleaning means, a dedicated cleaning means for cleaning the surface of the carrier is provided. There is no need to provide it, and the apparatus can be downsized.

  A sixth aspect of the present invention is the image forming apparatus according to any one of the first to fifth aspects, wherein the pattern image formed on the image carrier is applied to the intermediate transfer by applying a transfer bias. A transfer means for electrostatically transferring from a body to the transport body, and applying a bias having a polarity opposite to the transfer bias to the transfer means, whereby the pattern image on the transport body is applied to the intermediate transfer body. It is configured to transfer electrostatically.

  Since the pattern image transferred to the carrier is charged to the same polarity as the charged polarity at the time of transfer, applying a bias having a polarity opposite to the transfer bias to the transfer means causes the pattern image to be intermediate from the carrier. An electrostatic biasing force toward the transfer body can be generated. As described above, the pattern image can be transferred from the conveyance body to the intermediate transfer body only by changing the polarity of the bias applied to the transfer means.

  A seventh aspect of the present invention is the image forming apparatus according to any one of the first to sixth aspects, wherein the pattern image formed on the image carrier is applied to the intermediate transfer by applying a transfer bias. A transfer means for electrostatically transferring to the transport body without passing through a body, and applying a bias having a polarity opposite to that of the transfer bias to the transfer means, thereby transferring the pattern image on the transport body to the intermediate It is configured to electrostatically transfer to the image carrier without passing through a transfer member.

  Since the pattern image transferred to the carrier is charged with the same polarity as the charged polarity at the time of transfer, applying a bias having a polarity opposite to the transfer bias to the transfer means causes the pattern image to be transferred from the carrier to the pattern image. An electrostatic urging force toward the carrier can be generated. In this way, the pattern image can be transferred from the carrier to the image carrier only by changing the polarity of the bias applied to the transfer means.

  According to an eighth aspect of the present invention, in the image forming apparatus according to the sixth or seventh aspect, there is provided charging means for charging the pattern image on the transport body to the same polarity as the charge polarity at the time of transfer to the transport body. It is a thing.

  As described above, the pattern image transferred onto the carrier is charged with the same polarity as the charging polarity at the time of transfer, but the charged charge of the pattern image may be reduced with the passage of time. Therefore, by recharging the pattern image on the transport body to the same polarity as the charging polarity at the time of transfer by the charging means, it is possible to reliably transfer the pattern image from the transport body to the intermediate transfer body or the image carrier. Become

  According to a ninth aspect of the present invention, in the image forming apparatus according to the eighth aspect, the image forming apparatus further includes a suction unit that electrostatically sucks the recording medium onto the transport body when a suction bias is applied. , And used as the charging means for charging the pattern image.

  Since the suction means also functions as a charging means for charging the pattern image, it is not necessary to provide a dedicated charging means, and the apparatus can be downsized.

  The invention of claim 10 is the image forming apparatus according to any one of claims 1 to 9, wherein the pattern image is a pattern image for detecting image displacement, a pattern image for detecting image density, or Both a pattern image for detecting image displacement and a pattern image for detecting image density are used.

  By detecting the pattern image, it is possible to perform image positional deviation correction, image density correction, or both.

  According to an eleventh aspect of the present invention, in the image forming apparatus according to any one of the first to tenth aspects, whether or not to form the pattern image is determined according to the number of times of subsequent image formation. It is a thing.

  In general, when the number of times of subsequent image formation is small, the possibility that image correction is necessary is reduced. In such a case, it is possible to reduce the consumption of the developer used for forming the pattern image by not forming the pattern image.

  According to a twelfth aspect of the present invention, in the image forming apparatus according to any one of the first to eleventh aspects, at least a black image is formed on the image carrier that transfers an image without passing through the intermediate transfer member. Image carrier.

  In this case, the black image is improved because the black image is transferred to the recording medium without using the intermediate transfer member.

  A thirteenth aspect of the present invention is the image forming apparatus according to any one of the first to twelfth aspects, wherein the toner used as the developer for forming the pattern image has a circularity of 0.92 or more. Alternatively, the shape factor SF-1 is in the range of 100 to 180, and the shape factor SF-2 is in the range of 100 to 180.

  Thereby, since the shape of the toner becomes a substantially spherical shape, the attractive force between the toner and the attractive force between the toner and the toner carrying surface are weakened, and the transfer rate is improved.

  A fourteenth aspect of the present invention is the image forming apparatus according to any one of the first to thirteenth aspects, wherein the intermediate transfer body and the transport body are configured to be detachable from the main body of the image forming apparatus. .

  Since the intermediate transfer member and the transport member can be attached to and detached from the image forming apparatus main body, their maintainability is improved.

  According to the present invention, a pattern image can be detected and image correction can be performed without stopping the image forming operation even during the subsequent image formation. As a result, an increase in the waiting time of the user can be suppressed and high image quality can be realized.

1 is a schematic configuration diagram of a color image forming apparatus of the present invention. 1 is a schematic configuration diagram of an image forming apparatus during monochrome image formation. It is a top view of a conveyance belt. It is a figure which shows an example of the relationship between the circumference of a conveyance belt, a paper part, and between paper. It is a figure which shows another example of the relationship between the circumference of a conveyance belt, a paper part, and between paper. It is a figure which shows an example of the timing chart in which a voltage is applied to a direct transfer roller. It is a figure which shows an example of the timing chart in which a voltage is applied to a drive roller. FIG. 2 is a schematic configuration diagram of an image forming apparatus in which a black process unit is disposed on the downstream side in the recording medium conveyance direction with respect to an intermediate transfer belt. 4A and 4B are diagrams schematically illustrating the shape of a toner, where FIG. 5A is an explanatory diagram of a shape factor SF-1, and FIG. 5B is an explanatory diagram of a shape factor SF-2. 1 is a schematic configuration diagram of an image forming apparatus configured to directly transfer only a black image.

  FIG. 1 is a schematic configuration diagram of a color image forming apparatus according to the present invention. The image forming apparatus shown in FIG. 1 includes process units 1Y, 1C, 1M, and 1Bk as four image forming units configured to be detachable from the image forming apparatus main body 10. The process units 1Y, 1C, 1M, and 1Bk have the same configuration except that they contain toners of different colors of yellow, cyan, magenta, and black corresponding to the color separation components of the color image.

  Specifically, each of the process units 1Y, 1C, 1M, and 1Bk is provided on the photosensitive member 2 as an image carrier, a charging roller 3 as a charging unit that charges the surface of the photosensitive member 2, and the surface of the photosensitive member 2. A developing device 4 as a developing unit that supplies toner (developer) and a cleaning blade 5 as an image carrier cleaning unit that cleans the surface of the photoreceptor 2 are provided. The cleaning means is not limited to the cleaning blade. A fur brush roller, a magnetic brush, or the like may be applied as the cleaning means.

  On the upper part of the image forming apparatus main body 10, a scanner 9 for reading an image of a document is disposed. On the other hand, in the lower part of the image forming apparatus main body 10, paper feed trays 15 and 16 that accommodate recording paper P as a recording medium are provided.

  Under the yellow, cyan, and magenta process units 1Y, 1M, and 1C (hereinafter collectively referred to as “color process units”), the surface of the photoreceptor 2 is exposed to form an electrostatic latent image. An exposure device 6 is provided as means. In this embodiment, the exposure apparatus 6 employs a method of forming an electrostatic latent image with a laser, but is not limited to this, and may be an LED method or the like.

  An intermediate transfer device 7 is disposed above the color process units 1Y, 1C, 1M. The intermediate transfer device 7 has an endless belt-like intermediate transfer belt 8 as an intermediate transfer body onto which an image is transferred. The intermediate transfer belt 8 is stretched around a driving roller 19, a driven roller 20, and tension rollers 21 and 22. Further, four primary transfer rollers 11 as primary transfer means are disposed at positions facing the respective photoreceptors 2 of the color process units 1Y, 1C, and 1M via the intermediate transfer belt 8. Each primary transfer roller 11 is in contact with each photoreceptor 2 via an intermediate transfer belt 8, and a primary transfer nip is formed at a location where the intermediate transfer belt 8 and each photoreceptor 2 are in contact with each other.

  Above the intermediate transfer belt 8, four toner tanks 17Y, 17C, 17M, and 17Bk that store toners of yellow, cyan, magenta, and black are provided. These toner tanks 17Y, 17C, 17M, and 17Bk are connected to each developing device 4 through toner supply pipes 18Y, 18C, 18M, and 18Bk.

  On the left side of the intermediate transfer belt 8 in the figure, a belt cleaning device 13 is disposed as an intermediate transfer member cleaning unit that cleans the outer peripheral surface of the intermediate transfer belt 8.

  On the other hand, an endless belt-like transport belt 14 is disposed on the right side of the intermediate transfer belt 8 as a transport body that carries and transports the recording paper P. The conveyor belt 14 is stretched by a driving roller 23, a tension roller 24, a driven roller 31, a direct transfer roller 25 as a direct transfer unit, and a secondary transfer roller 26 as a secondary transfer unit.

  The direct transfer roller 25 is disposed at a position facing the photoconductor 2 of the black process unit 1Bk. The direct transfer roller 25 is in contact with the photosensitive member 2 via the conveyance belt 14, and a direct transfer nip is formed at a place where the photosensitive member 2 and the conveyance belt 14 are in contact with each other.

  The secondary transfer roller 26 is disposed at a position facing the driving roller 19 that drives the intermediate transfer belt 8. The secondary transfer roller 26 is in contact with the driving roller 19 via the conveyance belt 14 and the intermediate transfer belt 8, and a secondary transfer nip is formed at a position where the conveyance belt 14 and the intermediate transfer belt 8 are in contact with each other. Yes.

  A pair of registration rollers 27 for adjusting the timing of conveying the recording paper is disposed below the conveyance belt 14. On the other hand, a fixing device 12 for fixing an image on a recording sheet is disposed above the conveyor belt 14. A pair of paper discharge rollers 28 are disposed at the downstream end of the paper discharge path R1 formed above the fixing device 12. On the left side of the paper discharge roller 28 in the drawing, a paper discharge tray 29 for stocking the discharged recording paper is provided.

  Further, on the right side of the drawing of the image forming apparatus main body 10, there is provided a double-sided unit 30 that reverses the front and back of the recording paper for performing double-sided printing, and a conveyance path R <b> 2 for guiding the recording paper to the double-sided unit 30. Is branched from the paper discharge path R1.

Hereinafter, an image forming operation when a full-color image is formed in the image forming apparatus will be described with reference to FIG.
First, image information of a document read by the scanner 9 or image information based on received data such as a facsimile or data transmitted from a computer is decomposed into color information of yellow, cyan, magenta, and black and sent to the exposure device 6. Further, the photoreceptors 2 of the process units 1Y, 1C, 1M, and 1Bk are rotationally driven, and the surface of each photoreceptor 2 is uniformly charged to a predetermined polarity by the charging roller 3. Based on the information of each color, a laser is irradiated from the exposure device 6 to the surface of each photoconductor 2, and an electrostatic latent image is formed on the surface of each photoconductor 2. The electrostatic latent image formed on the photoreceptor 2 in this way is supplied with toner by each developing device 4, whereby the electrostatic latent image is visualized as a toner image.

  The recording paper P is sent out from the paper feed tray 15 or 16, and the recording paper P is timed by the registration roller 27 and sent to the conveying belt 14 rotating (circulating) in the direction of the arrow in the figure. Then, the black image formed on the photosensitive member 2 of the black process unit 1Bk is directly transferred onto the recording paper P in the direct transfer nip between the photosensitive member 2 of the black process unit 1Bk and the conveying belt 14. . Specifically, a transfer bias (voltage) having a polarity opposite to the charging polarity of the toner is directly applied to the transfer roller 25, and the black image on the photoreceptor 2 is electrostatically transferred to the recording paper P by this transfer bias. The

  On the other hand, the image formed on each photoconductor 2 of the color process units 1Y, 1M, and 1C other than black is rotated in the direction of the arrow in the figure at the primary transfer nip between each photoconductor 2 and the intermediate transfer belt 8. Primary transfer is performed so as to overlap on the intermediate transfer belt 8 (circular running). Specifically, a transfer bias (voltage) having a polarity opposite to the toner charging polarity is also applied to each primary transfer roller 11, and each color image on the photoreceptor 2 is electrostatically applied to the intermediate transfer belt 8 by this transfer bias. Is transferred to.

  The image on the intermediate transfer belt 8 is secondarily transferred to the recording paper P on which the black image has already been transferred at the secondary transfer nip between the intermediate transfer belt 8 and the conveyance belt 14. In this case, a transfer bias (voltage) having a polarity opposite to the toner charging polarity is applied to the secondary transfer roller 26, or a transfer bias (voltage) having the same polarity as the toner charging polarity is applied to the driving roller 19. Thus, the image on the intermediate transfer belt 8 is electrostatically transferred to the recording paper P. Thus, a full color image is transferred to the recording paper P.

  When a transfer bias having a polarity opposite to the charging polarity of the toner is applied to the secondary transfer roller 26, a high-voltage power supply for directly applying the transfer bias to the transfer roller 25 can be used. Since it is not necessary to provide a dedicated power source for applying a bias, the cost can be reduced and the image forming apparatus can be downsized. On the other hand, when a transfer bias having the same polarity as the charging polarity of the toner is applied to the driving roller 19, a voltage is applied to the toner via the intermediate transfer belt 8, so that even if the recording paper P absorbs moisture and the resistance decreases. Good transfer is possible.

  Thereafter, the recording paper P onto which the full-color image has been transferred is conveyed to the fixing device 12 where the image is fixed. Then, the recording paper P on which the image is fixed passes through the paper discharge path R 1, is discharged by the paper discharge roller 28, and is stocked on the paper discharge tray 29.

  When performing duplex printing, the recording paper P is guided to the transport path R <b> 2 and transported to the duplex unit 30. Then, the front and back sides of the recording paper P are reversed by the duplex unit 30, and the image is transferred and fixed on the back surface of the recording paper P through the same process as described above, and then the recording paper P is discharged to the paper discharge tray 29.

  Further, the residual toner adhering to the surface of each photoconductor 2 after the toner image is transferred is removed by the cleaning blade 5, and then the surface is subjected to a static elimination action by a static eliminator (not shown), and the surface potential is removed. Is initialized and prepared for the next image formation. Further, the toner remaining on the intermediate transfer belt 8 after the transfer is removed by the belt cleaning device 13.

  In this embodiment, the transfer of the black toner image is a direct transfer without using the intermediate transfer belt 8. By directly transferring the black image in this way, it is possible to reduce the number of components, and there is an advantage that the black writing image by the exposure device 6 can be written in the same direction without being inverted with respect to the other color image writing images. . Further, since direct transfer has higher transfer efficiency than indirect transfer performed via the intermediate transfer belt 8 or the like, the toner consumption of the black image formed on the photoreceptor 2 can be reduced. The present invention is not limited to the configuration in which the black image is directly transferred, and the image is transferred from the photosensitive member 2 of the black process unit 1Bk to a recording medium via an intermediate transfer member different from the intermediate transfer belt 8. It may be configured to transfer. However, in this case, since the black writing image by the exposure device 6 is inverted with respect to the writing image of the color image and becomes a mirror image, the writing control becomes complicated.

Next, a monochrome image forming operation for forming only a black toner image will be described.
When performing monochrome image formation, the secondary transfer roller 26 is separated from the intermediate transfer belt 8 in the direction of the arrow as shown in FIG. In conjunction with the separation of the secondary transfer roller 26, the conveyance belt 14 is displaced in a direction away from the intermediate transfer belt 8 by its own tension, so that the conveyance belt 14 is not in contact with the intermediate transfer belt 8.

  Then, a toner image is formed on the photosensitive member 2 of the black process unit 1Bk through the same process as described above in a state where the conveyance belt 14 is disposed in non-contact with the intermediate transfer belt 8, and the toner image is formed on the conveyance belt 14 The image is directly transferred onto the recording paper P conveyed by. Thereafter, the black image on the recording paper P is fixed by the fixing device 12, and the recording paper P is discharged to the paper discharge tray 29.

  If a monochrome image is formed with the conveyance belt 14 and the intermediate transfer belt 8 in contact with each other, the unfixed black image transferred to the recording paper P is stopped on the intermediate transfer belt 8. There is a possibility that the image is disturbed by the contact. In contrast, in this embodiment, when monochrome image formation is performed, the conveyance belt 14 and the intermediate transfer belt 8 are brought into a non-contact state so that the image on the recording paper P contacts the intermediate transfer belt 8. It can be avoided. This eliminates the need to drive the color process units 1Y, 1M, and 1C and the intermediate transfer belt 8 when forming a monochrome image, thereby extending the life of these units. Further, when full-color image formation is performed after monochrome image formation, the secondary transfer roller 26 is again brought closer to the intermediate transfer belt 8 side, and the conveying belt 14 is brought into contact with the intermediate transfer belt 8.

  In the above embodiment, the secondary transfer roller 26 is displaced. However, the entire conveyance belt 14 is displaced with the driven roller 31 as a fulcrum, and the conveyance belt 14 is brought into contact with and separated from the intermediate transfer belt 8. May be.

  Further, it is also possible to adopt a configuration in which the driving roller 19 that stretches the intermediate transfer belt 8 is moved closer to and away from the conveyance belt 14 and the intermediate transfer belt 8 is brought into contact with and separated from the conveyance belt 14. In this case, since it is not necessary to displace the conveyor belt 14, the behavior of the recording paper between the conveyor belt 14 and the fixing device 12 does not become unstable. For this reason, it is possible to prevent the recording paper after being discharged from the fixing device 12 from being wrinkled or disturbed. On the other hand, since the color images of the respective colors are superimposed on the intermediate transfer belt 8, if the intermediate transfer belt 8 is displaced, the image alignment accuracy may be deteriorated with time.

  In contrast, in this embodiment, the conveyance belt 14 is displaced, and the intermediate transfer belt 8 is stationary (not linked to the conveyance belt 14), so that there is no fluctuation in the tension of the intermediate transfer belt 8. Further, the intermediate transfer belt 8 can be kept in contact with the respective photoreceptors 2 that form a color image. For this reason, the positioning accuracy between the stretching rollers of the intermediate transfer belt 8 can be set high, and the margin with respect to the deviation of the belt is improved. In addition, by stabilizing the running of the intermediate transfer belt 8, it is possible to improve the margin against color misregistration (image misregistration) during full-color image formation.

  Conventionally, in an image forming apparatus in which the photosensitive members of all colors are brought into contact with the intermediate transfer belt, a mechanism for separating the intermediate transfer belt from the photosensitive members of colors other than black is also known. In this system, when the black image is formed, it is not necessary to drive the photoconductor other than black by separating the intermediate transfer belt from the photoconductor of a color other than black. However, in this case, since the intermediate transfer belt is displaced, it is unavoidable that the problem of the tension fluctuation of the intermediate transfer belt occurs.

  In addition, the image forming apparatus of the present invention is configured to be able to correct misalignment of each color image and image density correction. Hereinafter, a configuration and a correction operation for performing image misregistration correction and density correction will be described.

  By the pattern image forming means composed of the charging roller 3, the developing device 4, the exposure device 6, and the control unit for controlling them, the photosensitive members 2 of the process units 1Y, 1C, 1M, and 1Bk shown in FIG. A pattern image for image correction can be formed. This pattern image may be a pattern image for detecting an image position shift or a pattern image for detecting an image density. Alternatively, the pattern image may be both a pattern image for detecting image displacement and a pattern image for detecting image density.

  As shown in FIG. 1, pattern detection means 32 for detecting the pattern image is disposed at a position facing the conveyor belt 14. The pattern image detection means 32 is comprised with an optical sensor etc., for example. Further, a position detection means 33 for detecting the position of the surface of the conveyance belt 14 in the rotational direction and a charging means 34 for charging the surface (outer peripheral surface) of the conveyance belt 14 are disposed at a position facing the conveyance belt 14. ing. The position detection means 33 is configured to detect the position of the conveyance belt 14 in the rotational direction by detecting a reference position (not shown) provided on the conveyance belt 14.

  First, when full-color image correction is performed, a predetermined pattern latent image is formed by the exposure device 6 on the charged photoreceptors 2 of all the process units 1Y, 1C, 1M, and 1Bk. Then, the pattern latent image on each photoconductor 2 is developed by the developing device 4 to form a pattern image (toner image). The pattern image formed on the black photoreceptor 2 is transferred onto the conveying belt 14 by applying a transfer bias having a polarity opposite to the toner charging polarity directly to the transfer roller 25. On the other hand, the image formed on each photoconductor 2 of a color other than black is transferred to the intermediate transfer belt 8 by applying a transfer bias having a polarity opposite to the charging polarity of the toner to the primary transfer roller 11, and then the secondary transfer roller. The toner image is transferred from the intermediate transfer belt 8 to the conveying belt 14 by applying a transfer bias having a polarity opposite to the toner charging polarity to the toner 26 or applying a transfer bias having the same polarity as the toner charging polarity to the driving roller 19. .

  In this way, when the pattern image of each color is transferred, the conveyor belt 14 rotates, and when the pattern image on the conveyor belt 14 reaches the position of the pattern image detector 32, each pattern image is detected by the pattern image detector 32. Is detected. Then, based on the detection result, a control unit (not shown) controls the image forming conditions to correct the image misalignment and the image density.

  Thereafter, when the pattern image on the conveyance belt 14 reaches the position of the direct transfer roller 25, a bias having a polarity opposite to the above-described transfer bias is applied to the direct transfer roller 25. At this time, since the pattern image on the conveyance belt 14 is charged with the same polarity as the charging polarity when transferred to the conveyance belt 14, the transfer roller 25 is directly charged with the opposite polarity to the transfer bias. An electrostatic urging force from the conveyor belt 14 toward the black photosensitive member 2 acts on the pattern image. Therefore, the pattern image is transferred from the conveyor belt 14 to the black photosensitive member 2. The pattern image transferred to the black photoconductor 2 is removed by a cleaning blade 5 provided on the black photoconductor 2.

  As described above, by transferring the pattern image from the conveyance belt 14 to the black photosensitive member 2, the pattern image basically disappears from the conveyance belt 14, but in this embodiment, the pattern on the conveyance belt 14 is further reduced. When the portion where the image has been transferred reaches the position of the secondary transfer roller 26, a bias having a polarity opposite to that of the transfer bias is applied to the secondary transfer roller 26 or the driving roller 19. As a result, an electrostatic urging force from the conveyance belt 14 toward the intermediate transfer belt 8 is generated on the pattern image remaining on the conveyance belt 14, and the pattern image is transferred to the intermediate transfer belt 8. The pattern image transferred to the intermediate transfer belt 8 is removed by a belt cleaning device 13 provided on the intermediate transfer belt 8.

  Next, when performing black-only image correction, as shown in FIG. 2, the secondary transfer roller 26 is separated from the intermediate transfer belt 8 in the direction of the arrow, and the conveying belt 14 is moved to the intermediate transfer belt 8. On the other hand, it is in a non-contact state. In this state, a pattern image is formed on the photosensitive member 2 of the black process unit 1Bk in the same manner as described above, and a transfer bias is directly applied to the transfer roller 25, whereby the black photosensitive member 2 and the conveying belt 14 are applied. Transfer the pattern image to On the other hand, the color process units 1Y, 1C, 1M other than black and the intermediate transfer belt 8 are not driven.

  Then, the pattern image on the conveyor belt 14 is detected by the pattern image detecting unit 32, and the image density of the black image is corrected based on the detection result. After the detection by the pattern image detecting means 32, when the pattern image on the conveyance belt 14 reaches the position of the direct transfer roller 25, a bias having a polarity opposite to the transfer bias is applied to the direct transfer roller 25, thereby the pattern image. Is transferred from the conveyor belt 14 to the black photoreceptor 2. The pattern image transferred to the black photoconductor 2 is removed by a cleaning blade 5 provided on the black photoconductor 2.

  As described above, in the image forming apparatus of the present invention, the pattern image on the conveyance belt 14 is transferred to the black photoreceptor 2 or the intermediate transfer belt 8 and removed by the cleaning means provided on each of the patterns. Since there is no need to provide a dedicated cleaning means for removing the pattern image on the belt 14, the apparatus can be reduced in size. In the above embodiment, in full color image correction, the collection of the pattern image on the conveyor belt 14 is performed by both the black photoreceptor 2 and the intermediate transfer belt 8, but the image is transferred to either one. You may make it collect | recover.

  Further, as described above, the pattern image on the conveyor belt 14 is charged to the same polarity as the charged polarity when transferred to the conveyor belt 14, but the charged charge of the pattern image decreases with time. Is also possible. Therefore, in this embodiment, after the pattern image on the conveying belt 14 is detected by the pattern image detecting unit 32, the pattern image is recharged to the same polarity as the charging polarity at the time of transfer to the conveying belt 14 by the charging unit 34. Thus, the transfer of the pattern image from the transport belt 14 to the black photosensitive member 2 or the intermediate transfer belt 8 can be reliably performed.

  In addition, the image forming apparatus of the present invention is configured to perform image correction by detecting a pattern image while performing image formation continuously even when image formation is performed a plurality of times. Hereinafter, a specific method of this image correction will be described in detail.

  When image formation is continuously performed a plurality of times, the recording paper is continuously conveyed by the conveyance belt 14 at a predetermined interval. Therefore, as shown in FIG. 3, the surface of the transport belt 14 is divided into a recording medium carrying area G carrying the recording paper P and a non-carrying area H between the recording medium carrying areas G. Hereinafter, for convenience, the “recording medium carrying area” is referred to as “paper portion” and the “non-carrying area” is referred to as “paper space”. In the image forming apparatus according to the present invention, the same area on the conveyor belt 14 is controlled to be between the paper portion and the sheet for each cycle of the rotation of the conveyor belt 14.

FIG. 4 shows an example of the relationship between the circumference of the conveyor belt and the paper portion and the space between the paper.
In FIG. 4, the circumferential length of the conveyance belt is represented as Lb, and the length of the recording sheet in the conveyance direction (paper portion) is represented as Lp. Here, a case where one recording sheet is conveyed while the conveying belt makes one rotation is taken as an example. That is, the relationship is Lp ≦ Lb <2Lp. In this case, the paper belt and the paper space are divided one by one on the conveyance belt for each cycle, and the paper portion and the paper space in each cycle are controlled to be the same area on the conveyance belt. .

FIG. 5 shows another example of the relationship between the circumference of the conveyor belt and the paper portion and the space between the paper.
FIG. 5 shows an example in which two recording sheets are conveyed while the conveying belt makes one rotation. That is, the relationship is 2Lp ≦ Lb <3Lp. In this case, the paper belt and the paper space are divided into two each for each cycle on the transport belt, and the paper portion and the paper space in each cycle are controlled to be the same region on the transport belt. .

  When three or more recording sheets are conveyed while the conveying belt is rotated once, the sheet interval between the sheets in each cycle is adjusted on the conveying belt by adjusting the sheet interval as described above. What is necessary is just to set to the same area | region.

  For example, in the example shown in FIG. 4, when performing image correction while forming an image, first, the first printing image is formed on each photoconductor, and each image is printed on the first turn on the conveyor belt. Transfer to the paper section (on the first recording sheet). Next, a pattern image is formed on each photoconductor, and each pattern image is transferred between the first round paper on the conveyor belt. Then, a second printing image is formed on each photoconductor, and each image is transferred to the second round paper portion (on the second recording paper) on the conveyor belt. Here, since the pattern image transferred between the first round paper is carried between the second round paper on the transport belt, this pattern image is reversed to the black photoreceptor or the intermediate transfer belt. Copy and collect. From the third round onward, the first and second rounds are repeated.

  In the case of the example shown in FIG. 5, a first printing image is formed on each photosensitive member, and each image is printed on the first paper portion (first recording paper on the first turn on the conveyor belt). Transfer to top). Next, a pattern image is formed on each photoconductor, and each pattern image is transferred between the first sheets of paper on the first turn on the conveyance belt. Then, a second printing image is formed on each photoconductor, and each image is transferred to the second paper portion (on the second recording paper) in the first turn on the transport belt. Further, a pattern image different from the pattern image formed first is formed on each photoconductor, and transferred between the second sheets of paper on the first turn on the conveyor belt. That is, in this case, unlike the case of FIG. 4, the pattern image is transferred between the next sheets before the pattern image transferred between the first sheets is collected.

  Then, a third printing image is formed on each photoconductor, and each image is transferred to the third paper portion (on the third recording paper) in the second turn on the conveyor belt. Since the pattern image transferred between the first paper is carried between the next three papers, the pattern image is reversely transferred to a black photoconductor or intermediate transfer belt and collected. Further, a fourth printing image is formed on each photoconductor, and each image is transferred to the fourth paper portion (on the fourth recording paper) in the second turn on the conveyor belt. Further, since the pattern image transferred between the second paper is carried between the next fourth paper, the pattern image is reversely transferred to a black photoconductor or intermediate transfer belt and collected. From the third round onward, the first and second rounds are repeated.

  FIG. 6 shows an example of a timing chart in which a voltage is applied to the direct transfer roller 25 (see FIG. 1) as the transfer means. The timing chart shown in FIG. 6 corresponds to the embodiment described in FIG. In this case, it is assumed that the toner of the image for printing and the pattern image is negatively charged.

  As shown in FIG. 6, when the first and second paper sections on the conveyance belt reach the position of the direct transfer roller 25, a positive transfer bias is applied to the direct transfer roller 25. Has been. As a result, the negative toner is attracted from the black photosensitive member to the conveying belt side, and the image is transferred to the first and second recording sheets. In addition, a positive transfer bias is applied to the direct transfer roller 25 even when the space between the first sheet of paper reaches the position of the direct transfer roller 25. As a result, the pattern image is transferred from the black photoreceptor to the paper on the conveyor belt. On the other hand, when the space between the second sheet of papers reaches the position of the direct transfer roller 25, a negative reverse transfer bias is applied to the direct transfer roller 25. As a result, the negative toner is repelled from the conveying belt toward the black photoconductor, and the pattern image transferred between the first round paper is reversely transferred to the black photoconductor. The applied voltage after the third round is controlled in the same manner as in the first and second rounds.

  FIG. 7 shows an example of a timing chart in which a voltage is applied to the drive roller 19 (see FIG. 1) as the transfer means. The timing chart shown in FIG. 7 also corresponds to the embodiment described in FIG. Also in this case, it is assumed that the toner of the printing image and the pattern image is negatively charged.

  As shown in FIG. 7, when the first and second paper sections on the conveyance belt reach the position of the transfer roller 25 directly, a negative transfer bias is applied to the drive roller 19. ing. As a result, the negative toner is repelled from the intermediate transfer belt toward the conveying belt, and the image is transferred to the first and second recording sheets. In addition, a negative transfer bias is applied to the driving roller 19 even when the interval between the first sheet of paper reaches the position of the driving roller 19. As a result, the pattern image is transferred from the intermediate transfer belt to the paper on the conveyance belt. On the other hand, when the interval between the second sheet of paper reaches the position of the driving roller 19, a positive reverse transfer bias is applied to the driving roller 19. As a result, the negative polarity toner is attracted from the conveyance belt to the intermediate transfer belt side, and the pattern image transferred between the first round paper is reversely transferred to the intermediate transfer belt. The applied voltage after the third round is controlled in the same manner as in the first and second rounds.

  In the above-described embodiment, either pattern image transfer or collection is performed for each sheet interval, but either one is not necessarily performed. For example, it is also possible to form a pattern image at a desired timing, for example, by transferring a pattern image between every tenth paper of the conveyor belt from the start of printing. Further, whether or not to form a pattern image may be determined according to the number of times of subsequent image formation. If the number of subsequent image formations is small, there is little risk of image displacement or density change. In such a case, toner consumption is reduced by not forming a pattern image. It is possible.

  In the above-described embodiment, image correction when full-color image formation is continuously performed has been described. However, when monochrome image formation is continuously performed, the same region is provided for each cycle of the transport belt as described above. Control may be performed so that there is a gap between sheets, and pattern images may be transferred and reversely transferred between the sheets.

  Further, the position detection means 33 shown in FIG. 1 detects the reference position on the conveyance belt and feeds back the detection result to the drive control of the conveyance belt. Accuracy is improved. In this embodiment, the position detection means 33 detects the reference position of the transport belt and starts image formation after moving the reference position to the home position. You may drive from.

  In addition, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. In the embodiment shown in FIG. 1, the image forming apparatus of the present invention has been described as a configuration in which the black process unit 1Bk is disposed upstream (downward in the drawing) in the recording medium conveyance direction with respect to the intermediate transfer belt 8. However, as shown in FIG. 8, the black process unit 1Bk may be arranged downstream of the intermediate transfer belt 8 in the recording medium conveyance direction (upper side in the drawing). In FIG. 8, the same reference numerals as those in FIG. 1 denote the same members or apparatuses as those in FIG.

  Further, in the image forming apparatus shown in FIG. 8, an adsorbing means 35 that electrostatically adsorbs the recording paper onto the conveyance belt 14 is disposed so as to face the outer peripheral surface of the conveyance belt 14. Here, a suction roller is used as the suction means 35, but an elastic brush or the like may be used. By applying a suction bias (voltage) to the suction means 35, a charge is applied to the recording paper transported on the transport belt 14, and the recording paper is electrostatically attracted to the transport belt 14. Thereby, it is possible to stabilize the transportability of the recording paper.

  Further, the suction means 35 may be used as the charging means 34 shown in FIG. In this case, by applying a bias of charging polarity at the time of transfer to the conveyance belt 14 to the pattern image transferred between the sheets on the conveyance belt 14 by the suction unit 35, the black photosensitive member 2 from the conveyance belt 14 is applied. Alternatively, the pattern image can be reliably transferred to the intermediate transfer belt 8. In addition, since the suction unit 35 also functions as a charging unit for recharging the pattern image, it is not necessary to provide a dedicated charging unit, so that the apparatus can be downsized.

  In the above-described embodiment, an intermediate transfer belt is used as an intermediate transfer body for transferring an image, and a conveyance belt is used as a conveyance body for conveying recording paper. It is also possible to apply other rotating bodies. Further, the intermediate transfer belt 8 and the conveyance belt 14 may be configured to be detachable from the image forming apparatus main body. Thereby, these maintainability improves. Further, the image forming apparatus according to the present invention may be a copying machine, a printer, a facsimile, or a complex machine thereof other than the apparatuses shown in FIGS.

  The toner used in the image forming apparatus of the present invention preferably has a circularity of 0.92 or more. Circularity SR = (peripheral length of a circle having the same area as the particle projection area / perimeter length of the particle projection image) × 100%. The closer the toner is to a true sphere, the closer to 100%. Alternatively, it is preferable to use a toner having a shape factor SF-1 in the range of 100 to 180 and a shape factor SF-2 in the range of 100 to 180.

FIG. 9 is a diagram schematically illustrating the shape of the toner. FIG. 9A is a diagram for explaining the shape factor SF-1, and FIG. 9B is a diagram for explaining the shape factor SF-2. The shape factor SF-1 indicates the ratio of the roundness of the toner shape and is represented by the following formula (1). This is a value obtained by dividing the square of the maximum length MXLNG of the shape formed by projecting the toner on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4.
SF-1 = {(MXLNG) ² / AREA} × (100π / 4) (1)
When the value of SF-1 is 100, the shape of the toner becomes a true sphere, and becomes larger as the value of SF-1 increases.

The shape factor SF-2 indicates the ratio of the unevenness of the toner shape, and is represented by the following formula (2). A value obtained by dividing the square of the perimeter PERI of the figure formed by projecting the toner on the two-dimensional plane by the figure area AREA and multiplying by 100π / 4.
SF-2 = {(PERI) ² / AREA} × (100π / 4) (2)
When the value of SF-2 is 100, there is no unevenness on the toner surface, and as the value of SF-2 increases, the unevenness of the toner surface becomes more prominent.

  As described above, the circularity of the toner is 0.92 or more, or the toner is in the range of 100 to 180 in terms of the shape factor SF-1 and in the range of 100 to 180 in terms of the shape factor SF-2 As a result, the shape of the toner is substantially spherical. When the toner is substantially spherical, the contact state between the toner and the toner or between the toner and the toner carrying surface becomes a point contact, so that the adsorbing force between the toners becomes weak and the fluidity becomes high. Further, the attractive force between the toner and the toner carrying surface is weakened, and the transfer rate is improved. By using such a substantially spherical toner, it becomes easy to reversely transfer the pattern image from the conveying belt to the black photosensitive member or the intermediate transfer belt, and the cleaning property of the conveying belt can be improved.

  As described above, according to the present invention, when the image formation is performed a plurality of times, the pattern image can be transferred between the papers on the transport belt, so that the recording paper can be continuously transported by the transport belt. The pattern image can be transferred. For this reason, it is possible to detect a pattern image and perform image correction without stopping the image forming operation, and it is possible to suppress an increase in the waiting time of the user and realize high image quality. . Further, in the above-described embodiment, since the same area on the conveyance belt is controlled so as to be between the paper portion and the paper every cycle of the rotation of the conveyance belt, the pattern image is transferred to the recording paper and becomes dirty. Can be prevented. Further, since the pattern image can be reliably transferred onto the conveyor belt, the reliability of image correction is also improved.

2 Photoconductor (image carrier)
5 Cleaning blade (Image carrier cleaning means)
8 Intermediate transfer belt (intermediate transfer member)
DESCRIPTION OF SYMBOLS 10 Image forming apparatus main body 13 Belt cleaning apparatus (intermediate transfer body cleaning means)
14 Conveyor belt (conveyor)
19 Drive roller (transfer means)
25 Direct transfer roller (transfer means)
26 Secondary transfer roller (transfer means)
32 Pattern detection means 33 Position detection means 34 Charging means 35 Adsorption means P Recording paper (recording medium)

JP 2006-201743 A

Claims (14)

A plurality of image carriers carrying images on the surface;
A carrier for carrying and carrying a recording medium;
An intermediate transfer member to which an image on the image carrier is transferred,
Among the plurality of image carriers, some of the images on the image carrier are transferred to the recording medium on the carrier via the intermediate transfer member, and the other images on the image carrier are In an image forming apparatus configured to be transferred to a recording medium on the conveyance body without passing through an intermediate transfer body,
Pattern image forming means for forming a pattern image for image correction on each image carrier;
A pattern image detecting means for detecting the pattern image on the carrier,
When performing image formation a plurality of times, the pattern image formed on each image carrier can be transferred between recording medium carrying regions carrying the recording medium on the carrier. An image forming apparatus. When the recording medium is a rotating body that conveys a recording medium while rotating the conveyance body, and the recording medium having the same conveyance direction length is conveyed continuously at a predetermined interval by the conveyance body,
The image forming apparatus according to claim 1, wherein the same area on the conveyance body is controlled to be the recording medium carrying area for each cycle of rotation of the conveyance body.   The image forming apparatus according to claim 2, further comprising a position detection unit configured to detect a position in a rotation direction of the surface of the conveyance body. Providing an intermediate transfer member cleaning means for cleaning the surface of the intermediate transfer member;
After the pattern image on the transport body is detected by the pattern image detection means, the pattern image on the transport body is transferred to the intermediate transfer body and cleaned by the intermediate transfer body cleaning means. The image forming apparatus according to claim 1. An image carrier cleaning means for cleaning the surface of the image carrier to transfer an image without passing through the intermediate transfer member;
After the pattern image on the transport body is detected by the pattern image detecting means, the pattern image on the transport body is transferred to the image carrier that transfers an image without passing through the intermediate transfer body, and The image forming apparatus according to claim 1, wherein the image forming apparatus is configured to be cleaned by an image carrier cleaning unit. A transfer means for electrostatically transferring the pattern image formed on the image carrier from the intermediate transfer body to the transport body by applying a transfer bias;
6. The apparatus according to claim 1, wherein the pattern image on the conveying member is electrostatically transferred to the intermediate transfer member by applying a bias having a polarity opposite to the transfer bias to the transfer unit. The image forming apparatus according to claim 1. A transfer means for electrostatically transferring the pattern image formed on the image carrier to the transport body without passing through the intermediate transfer body by applying a transfer bias;
By applying a bias having a reverse polarity to the transfer bias to the transfer means, the pattern image on the transport body is electrostatically transferred to the image carrier without passing through the intermediate transfer body. The image forming apparatus according to any one of claims 1 to 6.   The image forming apparatus according to claim 6, further comprising a charging unit configured to charge the pattern image on the transport body with the same polarity as a charge polarity at the time of transfer to the transport body. An adsorption means for electrostatically adsorbing the recording medium on the carrier by applying an adsorption bias;
The image forming apparatus according to claim 8, wherein the suction unit is used as the charging unit that charges the pattern image.   The pattern image is a pattern image for detecting an image position deviation, a pattern image for detecting an image density, or both a pattern image for detecting an image position deviation and a pattern image for detecting an image density. The image forming apparatus according to any one of the above.   11. The image forming apparatus according to claim 1, wherein whether or not to form the pattern image is determined according to the number of times of subsequent image formation.   The image forming apparatus according to claim 1, wherein the image carrier that transfers an image without passing through the intermediate transfer member is an image carrier on which at least a black image is formed.   The toner used as the developer for forming the pattern image has a circularity of 0.92 or more, or a shape factor SF-1 in the range of 100 to 180, and a shape factor SF-2 in the range of 100 to 180. The image forming apparatus according to claim 1, wherein the image forming apparatus is in a range of 180.   The image forming apparatus according to claim 1, wherein the intermediate transfer body and the transport body are configured to be detachable from a main body of the image forming apparatus.

Images