JP2005265951A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus maintaining a variation phase of a photoreceptor drum at a prescribed value by simple constitution at the time of substituting the photoreceptor drum without reducing component accuracy for suppressing periodical variation followed by the decentering of the photoreceptor drum and capable of continuing fine color registration after the substitution of the photoreceptor drum. <P>SOLUTION: In the image forming apparatus for successively transferring visible images formed on photoreceptor drums 3 on a plurality of image stations arranged in parallel in the rotational direction of an intermediate transfer belt to the intermediate transfer belt, the photoreceptor drums on respective image stations are coaxially linked to respective driving gears 502 through drum driving couplings 501. An engagement part 504 for engaging the rear flange of each photoreceptor drum with a drum driving coupling so as not move them in the peripheral direction, is arranged between the rear flange 32 of each photoreceptor drum and the drum driving coupling 501 only on one position in the peripheral direction on the axis of each drum driving coupling 501. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming apparatus such as a printer, and more particularly, to a measure for suppressing a shift of an image on a transfer material due to rotational blurring of a driving unit that drives an image carrier.

Conventionally, as an image forming operation of this type of image forming apparatus, an electrostatic latent image is formed on a photosensitive drum based on received image data. Then, toner is attached to the electrostatic latent image, and the image data is visualized on the photosensitive drum. Thereafter, the toner image on the photosensitive drum is transferred to the recording paper conveyed through the paper conveyance path. As a transfer method, a method in which a toner image on a photosensitive drum is directly transferred to a recording sheet (for example, see Patent Document 1), or a toner image on the photosensitive drum is primarily transferred to an intermediate transfer belt. After that, there is known a system in which the toner image on the intermediate transfer belt is secondarily transferred to a recording sheet (for example, see Patent Document 2). Then, the recording paper on which the toner image is transferred is passed through a fixing roller, and the toner image is fixed on the recording paper by heating and pressurizing with the fixing roller.
JP 2003-156915 A JP 2002-333780 A

  By the way, when a toner image on an image carrier such as a photosensitive drum is transferred to a recording sheet, a halftone is striped in a monochrome (monochrome) image, or on the image carrier for each of a plurality of image forming units. In the tandem type color electrophotographic process in which the toner images are sequentially transferred, highly accurate pixel alignment between the image forming units, so-called color registration, may be deteriorated. This is caused by the rotational angular velocity fluctuation of the image forming unit, and for this, it is important to reduce the fluctuation of the rotational angular velocity of the image forming unit, particularly the image carrier. Is characterized in that the longer the period of variation, the more prominent halftone stripes appear and the worse the color registration. In general, one rotation cycle of the image carrier and the drive gear (or pulley) that drives the image carrier is the longest cycle of the drive means, and this periodic variation is generally relative to the rotation center axis of the component. It is caused by eccentricity.

  Therefore, the central axis of the image carrier relative to the eccentricity of the image carrier is reduced in order to reduce the conspicuous halftone stripe pattern or the deterioration of color registration in the monochrome image due to the fluctuation equal to the rotation period of the image carrier. As a drive shaft, the shaft itself penetrated as a drive shaft, measures such as improving the accuracy of the image carrier to the limit, and holding the peripheral surface of the image carrier itself with ball bearings, etc. Measures are taken to eliminate the effects of.

  On the other hand, the drive gear (or pulley) for driving the image carrier is usually manufactured by an injection molded product of polyacetal, and the eccentricity with respect to the drive shaft is almost determined by the mold. In order to reduce this eccentricity, in general, there is no other way but to improve the component accuracy.

  However, if the accuracy of the parts of the image carrier and the drive gear (or pulley) is improved as described above, the yield is generally deteriorated, and a special molding machine is required to obtain high parts accuracy. It will be expensive. In addition, when the image carrier itself is held by a ball bearing, the inner diameter of the ball bearing becomes φ30 mm or more, resulting in a very expensive system.

  Therefore, it is conceivable not only to suppress periodic fluctuations accompanying the eccentricity of the image carrier with component accuracy, but also to maintain the eccentricity phase of the image forming unit at a predetermined value in addition to this. According to this, the halftone stripe pattern is reduced by maintaining the fluctuation phase of the image carrier at a predetermined value by making the halftone stripe pattern noticeable or the color registration deteriorated by high component accuracy. It is possible to ensure a good monochrome image or good color registration that has disappeared.

  However, with such a technique, when the image carrier is replaced, the fluctuation phase of the image carrier so far may be shifted. In this case, in order to ensure a good monochrome image or good color registration in which the halftone stripes disappear, control is performed so that the fluctuation phase of the image carrier is adjusted again to a predetermined value when the image carrier is replaced. In this case, there is an advantage that the original good state can be maintained, but there is a disadvantage that the control system becomes complicated.

  The present invention has been made in view of the above points, and an object of the present invention is to provide an image at the time of exchanging the image carrier without reducing the accuracy of components that suppress periodic fluctuations caused by eccentricity of the image carrier. An image that can maintain a fluctuating phase of the carrier at a predetermined value with a simple configuration and can continuously obtain a good monochrome image or a good color registration in which the halftone stripe pattern disappears even after the image carrier is replaced. It is to provide a forming apparatus.

  In order to achieve the above object, the solution of the present invention includes an image forming apparatus configured to form a good monochrome image in which a halftone stripe pattern disappears, and a tandem color electrophotographic process. An image forming apparatus configured to ensure good color registration is applied.

  First, an image forming apparatus configured to be able to form a good monochrome image in which a halftone stripe pattern disappears will be described.

  Specifically, the present invention includes an image forming unit that develops image information formed on the image carrier into a visible image, and the visible image on the image carrier of the image forming unit is applied to the image forming medium. On the premise of the image forming apparatus to be transferred, the image carrier of the image forming unit is coaxially connected to the drive means via the drive shaft. Then, the image carrier of the image forming unit and the driving unit are fitted between the image carrier of the image forming unit and the driving unit so as to be immovable in the circumferential direction only at a single circumferential position on the drive shaft. A fitting portion is provided.

  Due to this specific matter, when transferring a toner image on an image carrier such as a photosensitive drum to a recording sheet, an image carrier having improved component accuracy in reducing halftone stripes in a monochrome image, Drive means such as a drive gear (or pulley) is driven by a fitting portion so that the image carrier and the drive means are fitted so as not to move in the circumferential direction only at a single circumferential position on the drive shaft. Become. Therefore, if the image carrier and the driving means are fitted so that the eccentric phase of the image forming unit is maintained at a predetermined value at a predetermined position in the circumferential direction, the image carrier is replaced. Sometimes, the fluctuation phase of the image carrier that has been maintained at a predetermined value is not shifted, and the image carrier and the drive means are only at a single circumferential position on the drive shaft when the image carrier is replaced. The eccentric phase of the image forming unit is maintained at the predetermined value again by the fitting, and it is not necessary to control again to adjust the fluctuation phase of the image carrier to the predetermined value. Thus, the eccentric phase of the image forming unit is maintained in the original good state, and it is possible to continuously obtain a good monochrome image in which the halftone stripe pattern disappears even after replacement of the image carrier.

  On the other hand, an image forming apparatus configured to ensure good color registration in a tandem color electrophotographic process will be described.

  Specifically, according to the present invention, a plurality of image forming units that develop image information formed on an image carrier into a visible image are arranged in parallel in the transfer material moving direction, and the image carriers of these image forming units are arranged. On the premise of an image forming apparatus that sequentially transfers the above visible image to an image forming medium, the image carrier of each of the image forming units is coaxially connected to a driving unit via a driving shaft. . In addition, the image carrier of each image forming unit and the driving unit cannot be moved in the circumferential direction only at a single circumferential position on the drive shaft between the image carrier of each image forming unit and the driving unit. The fitting part which fits in is provided.

  Due to this specific matter, when transferring a toner image on an image carrier such as a photosensitive drum to a recording sheet, the image carrier of each image forming unit has improved the accuracy of parts to reduce the deterioration of color registration. The driving means such as the body and the driving gear (or pulley) is driven by the fitting portion so that the image carrier and the driving means are immovably fitted in the circumferential direction only at a single circumferential position on the driving shaft. Will do. For this reason, as long as the image carrier and the driving unit are fitted so that the eccentric phase of each image forming unit is maintained at a predetermined value at a predetermined position in the circumferential direction, any image forming unit When the image carrier is replaced, the fluctuation phase of each image carrier that has been maintained at a predetermined value does not deviate, and the image carrier and the driving means are connected to the drive shaft when the image carrier is replaced. The control is performed so that the phase of eccentricity of the image forming unit is maintained at a predetermined value again by fitting only at a single circumferential position on the upper side, and the fluctuation phase of the image carrier is adjusted again to the predetermined value. This is no longer necessary, and the eccentric phase of each image forming unit is maintained in its original good state with a very simple configuration, and it is possible to continue to obtain good color registration even after image carrier replacement. .

  In particular, the following configurations are listed as specifying the fitting portion.

  In other words, the fitting portion is configured to fit a drive shaft that is rotatably coupled to the drive means and a shaft shaft that is penetrated and supported at the center of the image carrier.

  By this specific matter, the shaft shaft at the center of the image carrier is coaxially fitted to the drive shaft of the drive means, and the influence of the eccentric component of the image carrier is suppressed as much as possible. This is very advantageous for continuously obtaining a good monochrome image or a good color registration in which the halftone stripe pattern after the replacement has disappeared.

  Further, a fitting portion provided at least in one circumferential direction on the drive shaft between the image carrier of the image forming unit and the drive unit is provided, and the image carrier of the image forming unit and the drive unit are provided as drive shafts. When the image carrier is formed in a key shape that can be relatively moved in the direction, the image carrier of the image forming unit and the driving means are relatively moved in the drive axis direction so that they can be easily fitted together. Can be performed smoothly.

  In the case where an urging means for urging the image bearing member in a direction in which the drive shaft is fitted is provided between the drive means and the drive shaft supported so as to be movable in the axial direction. Even when the image carrier and the drive means are not fitted when the image carrier is exchanged, when the image carrier is rotated to a position where it can be fitted by the rotation of the drive means, it is at a single point in the circumferential direction on the drive shaft. Only reliably can be fitted to the image carrier.

  In particular, the following configuration is listed as one that specifies a drive source that drives a drive unit coupled to the image carrier of a plurality of image forming units.

  That is, at least two drive sources are provided. Specifically, it is possible to use a driving source that drives a driving unit connected to an image forming unit that develops image information into a visible image with a black developer, and developer for each color other than black. Image formation for developing image information into a visible image with a black developer, including a total of two drive sources including a drive source that individually drives drive means connected to an image forming unit that develops a visual image A driving source that drives a driving unit that is connected to the image forming unit and a driving unit that is connected to an image forming unit that develops the image information into a visible image by using another three-color developer different from black are individually driven. A total of four drive sources including three drive sources are provided.

  Then, a detected portion for detecting the rotational phase provided in the driving means of each image forming section, a phase detecting means for individually detecting the rotational phase of the driving means by each detected section, and each of these phase detecting means And a control means for controlling the rotation of each drive source based on the individual rotation phase signals of the drive means detected by.

  By these specific matters, the drive source of the drive means connected to the image carrier of the plurality of image forming units is detected as needed, specifically, the rotational phase of the drive means is individually detected by each detected unit. Based on the rotation phase signal of each drive means from the phase detection means, the rotation of each drive source is individually controlled. As a result, the eccentric phase of each image forming unit is always maintained at a predetermined value even after the image carrier is replaced, and good color registration can be obtained effectively and continuously.

  Further, when a protrusion provided on the side surface of the driving unit is applied as the detected portion, the rotational phase signal of the driving unit can be smoothly detected by the transmission type phase detecting unit. On the other hand, when a reflecting plate provided on the side surface of the driving unit is applied as the detected portion, the rotational phase signal of the driving unit can be smoothly detected by the reflection type phase detecting unit. In addition, the image forming unit can be made compact by the reflection type phase detection means that is generally shorter in the thrust direction of the drive shaft than the transmission type phase detection means.

  Based on the rotational phase of the driving means rotating by the driving force from the predetermined driving source among the plurality of driving sources, the rotational phase of the driving means rotating by the driving force from the other driving source is set to a predetermined value. When the control means controls so as to maintain, the eccentric phase of each image forming unit is always maintained at a predetermined value, and good color registration can be continuously obtained more effectively. Is possible.

  In particular, the following configuration is listed as a means for specifying a driving unit for a plurality of image forming units.

  That is, a resin gear or pulley molded by injection molding is applied as each driving means.

  The resin gears or pulleys of all of the plurality of image forming units are formed by the same mold having only a single cavity formed by a die and a punch.

  Due to these specific matters, the resin gears or pulleys as the driving means are all molded with the same accuracy in each image forming unit, and the eccentric phase of each image forming unit is set to a predetermined value. It will be maintained smoothly, and good color registration can be obtained more continuously.

  In particular, the following configurations are listed as specifying the photosensitive drum.

  In other words, an element tube formed by applying a photoreceptor layer on the surface of a cylindrical aluminum alloy to the surface of the photosensitive drum, and press-fitted into one end of the element tube, and is fitted to the drive means via the drive shaft. A resin-made drive side flange and a resin-made non-drive side flange that is press-fitted into the other end of the base tube and supported by the image forming apparatus main body are provided.

  The resin-made drive side and non-drive side flanges of all of the plurality of image forming units are molded by the same mold having only a single cavity formed by a die and a punch, respectively. .

  Due to these specific matters, the driving side and the non-driving side flanges press-fitted into both ends of the raw tube constituting the photosensitive drum are all molded with the same accuracy in each image forming unit. Thus, the phase of the eccentricity of each image forming unit is smoothly maintained at a predetermined value, and good color registration can be smoothly and continuously obtained.

  In short, in short, even if the image carrier is replaced, the image carrier of the image forming unit and the driving means are fitted so as to be immovable in the circumferential direction only at a single circumferential position on the drive shaft. There is no deviation of the fluctuation phase, and there is no need to control the fluctuation phase of the image carrier again to a predetermined value, and the eccentric phase of the image forming unit is in an original good state with a very simple configuration. Thus, it is possible to continuously obtain a good monochrome image or a good color registration in which the halftone stripe pattern disappears after the exchange of the image carrier.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, a case where the present invention is applied to a color printer will be described.

(Description of overall configuration of image forming apparatus)
FIG. 1 schematically shows the internal configuration of an image forming apparatus A according to this embodiment. The image forming apparatus A generates a multicolor (full color) image or a single color (monochrome) image on a predetermined sheet (recording paper) according to image data transmitted from the outside (for example, a terminal device such as a personal computer). To form. As illustrated, the image forming apparatus A includes an exposure unit 1, a developing device 2 (2a to 2d), a photosensitive drum 3 (3a to 3d) as an image carrier, and a charger 5 (5a to 5d). The cleaner unit 4 (4a to 4d), the intermediate transfer belt unit 8, the fixing device 12, the paper transport path S, the paper feed cassette 10, the paper discharge tray 15, and the like.

  The image data handled in the image forming apparatus A corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y). Accordingly, the developing device 2 (2a to 2d), the photosensitive drum 3 (3a to 3d), the charger 5 (5a to 5d), and the cleaner unit 4 (4a to 4d) generate four types of latent images corresponding to the respective colors. In FIG. 1, a is set to black, b is set to cyan, c is set to magenta, and d is set to yellow to form four image stations (image forming units). ing.

  The photosensitive drum 3 is arranged (attached) on the upper part of the image forming apparatus A, and an electrostatic latent image corresponding to image data is formed by irradiation of laser light from the exposure unit 1 as will be described later. Yes. As shown in FIG. 2, the photosensitive drum 3 includes an element tube 31 formed by applying a photosensitive layer (not shown) on the surface of a cylindrical aluminum alloy, and one end ( A rear flange 32 as a resin drive side flange press-fitted into the right end in FIG. 2 and a front flange as a resin non-drive side flange press-fitted into the other end (left end in FIG. 2) of the raw pipe 31. 33, and a shaft shaft 34 that is rotatably connected to the rear flange 32 and the front flange 33, and is supported through the center of the base tube 31. The front flange 33 is rotatably supported on the front surface of the image forming apparatus A via a bearing (not shown).

  The charger 5 is a charging means for uniformly charging the surface (photosensitive member layer) of the photosensitive drum 3 to a predetermined potential. As shown in FIG. 1, a contact type roller type or brush type charger is provided. In addition, a charger-type charger may be used.

  The exposure unit 1 includes a laser scanning unit (LSU) including a laser irradiation unit 1A and reflection mirrors 1B, 1B,. The laser irradiation unit 1A irradiates laser light for each hue based on the received image data. In addition, there is a method using, for example, an EL or LED writing head in which light emitting elements are arranged in an array. The exposure unit 1 exposes the charged photosensitive drum 3 according to the input image data, thereby forming an electrostatic latent image according to the image data on the surface of the photosensitive drum 3. have.

  The developing device 2 visualizes the electrostatic latent images formed on the respective photosensitive drums 3 with toners (developers) of respective colors (K, C, M, Y).

  The cleaner unit 4 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer.

  The intermediate transfer belt unit 8 disposed above the photosensitive drum 3 includes an intermediate transfer belt 7, an intermediate transfer belt drive roller 71, an intermediate transfer belt tension mechanism 73, an intermediate transfer belt driven roller 72, and a primary transfer roller. An intermediate transfer roller 6 (6a to 6d) and an intermediate transfer belt cleaning unit 9 are provided.

  The intermediate transfer belt drive roller 71, the intermediate transfer belt tension mechanism 73, the intermediate transfer roller 6, and the intermediate transfer belt driven roller 72 are stretched over the intermediate transfer belt 7, and the intermediate transfer belt 71 is rotated along with the rotation of the intermediate transfer belt drive roller 71. The belt 7 travels in the direction of arrow B.

  The intermediate transfer roller 6 is rotatably supported by a roller mounting portion in the intermediate transfer belt tension mechanism 73. As a result, the intermediate transfer rollers 6 a to 6 d are rotatably disposed on the inner surface side of the intermediate transfer belt 7 facing each photoconductor drum 3, and the toner image on the photoconductor drum 3 is also provided. Is transferred to the intermediate transfer belt 7.

  The intermediate transfer belt 7 is provided so as to be in contact with each photosensitive drum 3. Then, the toner images of the respective colors formed on the photosensitive drum 3 are sequentially superimposed and transferred onto the intermediate transfer belt 7, thereby forming a color toner image (multicolor toner composite image) on the intermediate transfer belt 7. It is like that. The intermediate transfer belt 7 is endlessly formed using a film having a thickness of about 100 μm to 150 μm.

  Transfer of the toner image from the photosensitive drum 3 to the intermediate transfer belt 7 is performed by the intermediate transfer roller 6 in contact with the back side (inner surface side) of the intermediate transfer belt 7. That is, a high voltage transfer bias (a high voltage having a polarity (+) opposite to the toner charge polarity (−)) is applied to the intermediate transfer roller 6 in order to transfer the toner image. The intermediate transfer roller 6 is a roller whose base is a metal (for example, stainless steel) shaft having a diameter of 8 to 10 mm and whose surface is covered with a conductive elastic material (for example, EPDM, urethane foam, or the like). With this conductive elastic material, a high voltage can be uniformly applied to the intermediate transfer belt 7. In this embodiment, a roller electrode is used as the transfer electrode, but a brush or the like can also be used.

  As described above, the toner images visualized according to the hues on the photoreceptors 3a to 3d are stacked on the intermediate transfer belt 7 and become image information input to the apparatus. In this way, the laminated image information (composite image of multi-color toner) is transferred to a transfer roller that constitutes a transfer unit that is disposed at a contact position between a later-described sheet and the intermediate transfer belt 7 as the intermediate transfer belt 7 travels. 11 is transferred onto the paper.

  At this time, the intermediate transfer belt 7 and the transfer roller 11 are pressed against each other at a predetermined nip, and a voltage for transferring the toner onto the sheet is applied to the transfer roller 11 (opposite to the charging polarity (−) of the toner). Polarity (+) high voltage). Further, in order to obtain the nip constantly, the transfer roller 11 uses either the transfer roller 11 or the intermediate transfer belt drive roller 71 as a hard material (metal or the like) and the other as a soft material (elasticity such as an elastic roller). Rubber roller or foaming resin roller).

  Further, as described above, the toner adhered to the intermediate transfer belt 7 due to contact with the photosensitive drum 3 or the toner that is not transferred onto the sheet by the transfer roller 11 and remains on the intermediate transfer belt 7 Therefore, the intermediate transfer belt cleaning unit 9 removes and collects the toner. The intermediate transfer belt cleaning unit 9 includes a cleaning blade 91 as a cleaning member that comes into contact with the intermediate transfer belt 7. The intermediate transfer belt 7 contacts the intermediate transfer belt 7 in contact with the cleaning blade 91 from the back side. It is supported by a driven roller 72. The residual toner collected by the cleaning blade 91 falls and accumulates in a storage unit 92 installed below the cleaning blade 91.

  The paper feed cassette 10 is a cassette for storing sheets (recording paper) used for image formation, and is provided at the bottom of the image forming apparatus, that is, below the exposure unit 1. A paper discharge tray 15 provided in the upper part of the image forming apparatus is a tray for placing printed sheets face down.

  Further, the image forming apparatus A is provided with a paper transport path S for sending the sheets of the paper feed cassette 10 to the paper discharge tray 15 via the transfer roller 11 and the fixing device 12. The paper transport path S extends in a substantially vertical direction from the paper discharge unit of the paper feed cassette 10 toward the paper discharge tray 15. Further, a pickup roller 16 (16-1), a registration roller 14, a transfer roller 11, a fixing device 12, and a conveyance roller 25 (25) that conveys a sheet are provided in a paper conveyance path S from the paper cassette 10 to the paper discharge tray 15. -1,25-2, 25-3) and the like are disposed.

  The conveyance rollers 25 are small rollers for promoting and assisting conveyance of the sheet, and a plurality of conveyance rollers 25 are provided along the sheet conveyance path S. The pickup roller 16 is a drawing roller that is provided at the end of the paper feed cassette 10 and that feeds sheets one by one from the paper feed cassette 10 to the paper transport path S.

  Further, the registration roller 14 temporarily holds the sheet being conveyed on the sheet conveyance path S. The sheet has a function of conveying the sheet to a transfer unit (a nip portion between the transfer roller 11 and the intermediate transfer belt driving roller 71) at the timing when the leading edge of the toner image on the intermediate transfer belt 7 is aligned with the leading edge of the sheet. Yes.

  The fixing device 12 includes a heat roller 31, a pressure roller 32, and the like, and the heat roller 31 and the pressure roller 32 rotate with a sheet interposed therebetween. The heat roller 31 is set by the control unit to have a predetermined fixing temperature based on a signal from a temperature detector (not shown), and is transferred to the sheet by thermocompression bonding the sheet together with the pressure roller 32. The resulting multicolor toner image is melted, mixed, and pressed to thermally fix the sheet.

  The sheet after the fixing of the multicolor toner image is transported on the paper transport path S by the transport rollers 25, and is discharged onto the paper discharge tray 15 with the multicolor toner image facing downward. .

  Next, the sheet conveyance path will be described in detail. The image forming apparatus is provided with a paper feed cassette 10 that stores sheets in advance, and a manual feed tray 20 that does not need to open and close the paper feed cassette 10 when a user prints a small number of sheets. ing.

  In both paper feeding methods, pickup rollers 16 (16-1 and 16-2) are arranged, respectively, so as to guide one sheet to the conveyance path.

  The sheet conveyed from the sheet feeding cassette 10 is conveyed to the registration roller 14 by the conveying roller 25-1 in the conveying path, and is transferred to the transfer roller 11 at a timing when the leading edge of the sheet and the leading edge of the image information on the intermediate transfer belt 7 are aligned. The image information is written on the sheet. Thereafter, the sheet passes through the fixing device 12, whereby unfixed toner on the sheet is melted and fixed by heat, and is discharged from the discharge roller 25-3 onto the discharge tray 15 through the conveyance roller 25-2 ( (When requesting single-sided printing)

  On the other hand, the sheets stacked on the manual feed tray 20 are fed by the pickup roller 16-2, reach the registration roller 14 through a plurality of transport rollers (25-6, 25-5, 25-4), and thereafter. The sheet is discharged from the sheet feeding cassette 10 to the sheet discharge tray 15 through the same process as that of the sheet fed (when single-side printing is requested).

  At this time, if the print request content is a double-sided print request, the trailing edge of the sheet that has finished single-sided printing and passed through the fixing device 12 as described above is chucked by the paper discharge roller 25-3, and the paper discharge roller 25 -3 reversely rotates and is guided to the switchback conveyance path S1 provided with the conveyance rollers (25-7, 25-8), then the back side printing is performed through the registration rollers 14, and then the paper discharge tray. 15 will be discharged.

  In the actual image forming operation, the intermediate transfer roller 6 is subjected to intermediate transfer in response to a print request in order to reduce deterioration of the photosensitive drum 3 due to contact between the intermediate transfer belt 7 and the photosensitive drum 3. The intermediate transfer belt 7 and the photosensitive drum 3 can be separated from each other by moving the belt 7 in a direction in which the belt 7 is in contact with or separated from the belt 7.

  That is, the print request includes a color mode and a monochrome mode. In the color mode, each intermediate transfer roller 6 (6a to 6d) moves so as to come into contact with the back surface of the intermediate transfer belt 7, thereby performing the intermediate transfer. The surface of the belt 7 and each of the photosensitive drums 3 (3a to 3d) come into contact with each other so that the toner image of each hue can be primarily transferred to the intermediate transfer belt 7. On the other hand, in the monochrome mode, only the intermediate transfer roller 6a for black image formation moves so as to come into contact with the back surface of the intermediate transfer belt 7, thereby the surface of the intermediate transfer belt 7 and the photosensitive drum for black image formation. 3a comes into contact with the black toner image so that it can be primarily transferred to the intermediate transfer belt 7.

(Drive mechanism)
Next, the drive mechanism 50 which is a characteristic part of the present invention will be described with reference to FIGS.

  As shown in FIGS. 3 and 4, the drive mechanism 50 is connected to the photosensitive drums 3 (3a to 3d) of the four image stations with a drive gear shaft 505 and a shaft shaft 34 coaxially as drive shafts. Then, driving means having a drum driving coupling 501 and a driving gear 502 around the driving gear shaft 505, and driving motors 503-1 and 503 as driving sources for driving the driving gears 502 (502a to 502d). 2 and a fitting portion 504 for fitting the drum drive coupling 501 of each of the drive gears 502 (502a to 502d) and the rear flange 32 of the photosensitive drum 3 (3a to 3d).

  The drum drive coupling 501 is supported so as to be movable in the axial direction and non-movable in the circumferential direction via a key (not shown) with respect to the drive gear shaft 505 that is rotatably coupled to the drive gear 502. As shown in FIGS. 5A to 5C, a stopper 506 is fixed on the drive gear shaft 505 closer to the drive gear 502 than the drum drive coupling 501. A biasing spring 507 serving as a biasing means for biasing the drum driving coupling 501 to the rear flange 32 of the photosensitive drum 3 (rear flange 32 side) is provided between the driving coupling 501 and the driving coupling 501. It is disguised.

  One drum drive motor 503-1 of the drum drive motors 503-1 and 503-2 drives the photosensitive drum 3a of the image station in which the toner color is set to black, and the other drum drive motor. The motor 503-2 drives the photosensitive drums 3 b to 3 d of the image stations whose toner colors are set to cyan, magenta, and yellow. The output gear 503-1a of the one drum drive motor 503-1 is connected to the intermediate transfer belt drive gear 71-1 which is connected to the intermediate transfer belt drive roller 71 so as to rotate integrally therewith. The drive gear 502a is connected to the photosensitive drum 3a of the image station in which the toner color is set to black and is connected to the large and small intermediate gears 503-11 and 503-12. On the other hand, the large-diameter intermediate gear 503-13 and two large and small intermediate gears 503-14 and 503-15 that are coaxially connected to each other are connected so as to be able to transmit power. The output gear 503-2a of the other drum drive motor 503-2 has two intermediate gears 503 having a larger diameter than the drive gear 502b connected to the photosensitive drum 3b of the image station whose toner color is set to cyan. -16, 503-17 and two large and small intermediate gears 503-18 and 503-19 that are coaxially connected to each other so as to be able to transmit power, and the toner color is set to magenta With respect to the drive gear 502c connected to the photosensitive drum 3c of the image station, two large-diameter intermediate gears 503-20 and 503-21 and two large and small intermediate gears 503-22 coaxially and integrally connected to each other. , 503-23 to be able to transmit power, and the photosensitive drum 3 of the image station in which the toner color is set to yellow The intermediate gears 503-20 and 503-21 having a large diameter and the two large and small intermediate gears 503-24 and 503-25 that are coaxially and integrally connected to the drive gear 502d connected to Are connected so that power can be transmitted.

  The fitting portion 504 is a key-shaped protrusion 504-1 that protrudes radially outward at three predetermined intervals in the circumferential direction on the outer peripheral surface of the drum drive coupling 501 of each drive gear 502 (502a to 502d). , 504-2, 504-3, and a key groove shape recessed radially outward at three locations at predetermined intervals in the circumferential direction on the inner peripheral surface of the rear flange 32 of the photosensitive drum 3 (3a to 3d). The concave portions 504-4, 504-5, and 504-6 are provided. One of the protrusions 504-1, 504-2, and 504-3 has a larger width in the circumferential direction than the other protrusions 504-2 and 504-3. . In addition, one of the recesses 504-4, 504-5, and 504-6 has a width in the circumferential direction larger than that of the other recesses 504-5 and 504-6. Only one protrusion 504-1 having a large circumferential width is fitted into only the recess 504-4 having a large circumferential width. By such a fitting portion 504, the photosensitive drum 3 (rear flange 32) and the drive gear 502 (drum drive coupling 501) are axially connected only at a single circumferential position on the axis of each drum drive coupling 501. It is adapted to be able to move relative to each other and not to move in the circumferential direction. Furthermore, the tip of the drive gear shaft 505 (photosensitive drum 3 side end) is fitted into a through hole 32 a that passes through the center of the rear flange 32. A hole 505a is provided at the front end of the drive gear shaft 505, and the rear end of the shaft shaft 34 of the photosensitive drum 3 is fitted into the hole 505a, so that the drive gear shaft 505, the shaft shaft 34, Is designed to fit.

  As shown in FIG. 6, a protrusion 502-1 as a detected portion for detecting the rotational phase of the drive gear 502 is formed on the front side surface (side surface of the photosensitive drum 3) of each of the drive gears 502 (502a to 502d). Is protruding. Further, as shown in FIG. 4, one side of the rear side of the photosensitive drum 3a of the image station in which the toner color is set to black and the photosensitive drum 3b of the image station in which the toner color is set to cyan ( On the left side in FIG. 4, transmission type photo interrupters 508 and 508 are provided as phase detection means for individually detecting the rotational phase of the drive gear 502 by the protrusion 502-1. Then, based on the individual rotation phase signals of the drive gears 502 (502a to 502d) detected by the photo interrupters 508, the rotation of the drum drive motors 503-1 and 503-2 is controlled by the control unit. Yes. This control unit uses the rotation phase of the drive gear 502a that is rotated by the drive force of one of the two drum drive motors 503-1 and 503-2 as a reference, and the other drum drive motor. Control is performed so that the rotational phase of the drive gears 502b to 502d rotated by the driving force 503-2 is maintained at an allowable value (predetermined value).

  Further, all the drive gears 502 (502a to 502d) of each image station are injected by a so-called single die having the single cavity formed by a die and a punch (not shown) or the same die. Molded. Further, the rear flanges 32 of all the photosensitive drums 3 (3a to 3d) of each image station have a so-called single die, that is, the same mold having only a single cavity surrounded by a die and a punch (not shown). On the other hand, the front flanges 33 of all the photosensitive drums 3 (3a to 3d) of each image station also have only a single cavity formed by a die and a punch (not shown). It is injection-molded by a so-called single die having the same die.

  Therefore, in the above-described embodiment, when the toner image on the photosensitive drum 3 (3a to 3d) is transferred to the sheet, the sensitivity of each image station that improves the component accuracy in reducing the deterioration of color registration. The body drums 3a to 3d and the drive gear 502 (502a to 502d) are driven by the fitting portion 504 with the photosensitive drum 3 (rear flange 32) only at a single circumferential position on the axis of each drum drive coupling 501. The gear 502 (drum drive coupling 501) is fitted and driven so as to be relatively movable in the axial direction and immovable in the circumferential direction. For this reason, the photosensitive drum 3 (rear flange 32) and the drive gear 502 (drum drive coupling 501) are arranged so that the eccentric phase of each image station is maintained at a predetermined value at a predetermined position in the circumferential direction. If fitted, the photoconductive drum 3 is maintained at a predetermined value when the photoconductive drum 3 of an arbitrary image station is replaced. 3 is exchanged, the photosensitive drum 3 and the drive gear 502 are fitted only at a single circumferential position on the axis of each drum drive coupling 501, and the eccentric phase of the image station is maintained at a predetermined value again. Therefore, it becomes unnecessary to control the fluctuation phase of the photosensitive drum 3 again to a predetermined value, and the eccentricity of each image station can be reduced with a very simple configuration. The phases can be maintained at its original good state, it is possible to photoreceptor drum 3 after the replacement may also continue a good color registration.

  The fitting portion 504 is a key-shaped protrusion 504 that protrudes radially outward at three predetermined intervals in the circumferential direction on the outer peripheral surface of the drum drive coupling 501 of each drive gear 502 (502a to 502d). -1, 504-2, 504-3, and keys that are recessed radially outward at three circumferentially spaced intervals on the inner peripheral surface of the rear flange 32 of the photosensitive drum 3 (3a to 3d). Since the groove-shaped recesses 504-4, 504-5, and 504-6 are provided, the rear flange 32 of the photosensitive drum 3 (3a to 3d) and the driving gears 502 (502a to 502d) of each image station are provided. The drum drive coupling 501 is relatively moved in the axial direction to be easily fitted, and the replacement work of the photosensitive drum 3 (3a to 3d) can be performed smoothly.

  The drum drive coupling 501 is arranged between the stopper 506 closer to the drive gear 502 than the drum drive coupling 501 on the drive gear shaft 505 and the drum drive coupling 501 of the drive gear 502. Since the urging spring 507 for urging in the direction (rear flange 32 side) to be fitted to the flange 32 is contracted, the photosensitive drum 3 is exposed when the photosensitive drum 3 is replaced as shown in FIG. Even if the rear flange 32 of the body drum 3 and the drum drive coupling 501 of the drive gear 502 are not fitted, the drum drive coupling 501 is rotated by the rotation of the drive gear 502 as shown in FIG. , The protrusions 504 of the drum drive couplings 501 of the drive gears 502 (502a to 502d) , 504-2, 504-3 and the recesses 504-4, 504-5, 504-6 of the rear flange 32 match each other, as shown in FIG. It can be surely fitted to the rear flange 32 of the photosensitive drum 3 only at the location.

  Further, the rear end of the shaft shaft 34 of the photosensitive drum 3 is inserted into the hole 505a at the front end (end of the photosensitive drum 3) of the driving gear shaft 505, and the driving gear shaft 505 and the shaft shaft 34 are fitted. Therefore, the shaft shaft 34 at the center of the photosensitive drum 3 is coaxially fitted to the drum driving coupling 501 of the driving gear 502, and the influence of the eccentric component of the photosensitive drum 3 is affected. Is suppressed as much as possible, which is very advantageous in obtaining good color registration after the replacement of the photosensitive drum 3.

  Two drum drive motors 503-1 and 503-2 are provided, and one of the drum drive motors 503-1 is a drive gear 502a that drives the photosensitive drum 3a of the image station in which the toner color is set to black. The other drum drive motor 503-2 is connected to drive gears 502b to 502d for driving the photosensitive drums 3b to 3d of the image stations whose toner colors are set to cyan, magenta, and yellow. The rotation phase of each drive gear 502 is individually detected by a projection 502-1 provided on the front side surface (side surface of the photosensitive drum 3) of the drive gear 502 (502a to 502d), and the detected drive gear 502 ( 502a to 502d) based on the individual rotational phase signals of the drum drive motors 503-1 and 503-2. Are controlled by the control unit, so that the drum drive motors 503-1 and 503-2 of the drive gear 502 (502a to 502d) connected to the photosensitive drums 3 (3a to 3d) of a plurality of image stations are controlled. Specifically, each drum drive motor 503 is based on the individual rotation phase signals of the drive gears 502a to 502d from the photo interrupters 508 that individually detect the rotation phases of the drive gears 502a to 502d. The rotations of -1,503-2 are individually controlled. Thereby, the phase of the eccentricity of each image station is always maintained at a predetermined value, and good color registration can be effectively and continuously obtained even after the photosensitive drum 3 is replaced.

  In addition, the rotational phase of each drive gear 502 is individually detected by the projection 502-1 that projects from the front side surface (side surface of the photosensitive drum 3) of each drive gear 502 (502a to 502d), thereby transmitting the rotation. The rotational phase signals of the drive gears 502a to 502d can be smoothly detected by the type photo interrupter 508.

  In addition, the control unit drives the other drum on the basis of the rotational phase of the drive gear 502a that is rotated by the driving force of one of the two drum drive motors 503-1 and 503-2. Since the rotation phase of the drive gears 502b to 502d rotated by the driving force of the motor 503-2 is controlled to be an allowable value (predetermined value), the eccentric phase of each image station is always maintained at the predetermined value. As a result, good color registration can be obtained more effectively after the photosensitive drum 3 has been replaced.

  The resin drive gears 502a to 502d of all the image stations are formed by the same mold having only a single cavity formed by a die and a punch, and all of the image stations are Since the rear flange 32 and the front flange 33 are each formed by the same mold having only a single cavity formed by a die and a punch, the driving gears 502a to 502d of the respective image stations are formed. In addition, the rear flange 32 and the front flange 33 are all formed with the same accuracy in each image station, and the eccentric phase of each image station is smoothly maintained at a predetermined value. Even after the body drum is replaced, good color registration can be obtained even more. That.

  In the above embodiment, the photosensitive drum 3 (rear flange 32) and the photosensitive drum 3 are arranged only at a single circumferential position on the axis of each drum drive coupling 501 so as to maintain the eccentric phases of the plurality of image stations at a predetermined value. The case where the drive gear 502 (drum drive coupling 501) is fitted to reduce the deterioration of the color registration has been described. In an image forming apparatus for forming a monochrome image having only a single image station, the image station The halftone stripe pattern in a monochrome image is obtained by fitting the photosensitive drum and the drive gear only at a single circumferential position on the axis of the drum drive coupling so that the phase of the eccentricity is maintained at a predetermined value. You may apply when reducing. In this case, when the photosensitive drum is replaced, the fluctuation phase of the photosensitive drum, which has been maintained at a predetermined value until that time, is not shifted, and the photosensitive drum and the driving gear are not changed when the photosensitive drum is replaced. The phase of the eccentricity of the image station is maintained at a predetermined value again by fitting only at a single circumferential position on the axis of the drive coupling, and the fluctuation phase of the photosensitive drum is adjusted again to the predetermined value. It is no longer necessary to control the image, and the eccentric phase of the image station is maintained in its original good state with a very simple configuration. Can be obtained.

  In the above embodiment, the rotation phase of each drive gear 502 is individually detected by the transmission type photo interrupter 508 by the projection 502-1 protruding from the front side surface of each drive gear 502a to 502d. As shown in FIG. 7, a reflection plate 502-2 as a detected portion deposited on aluminum is stuck on the front side surface (side surface of the photosensitive drum) of the drive gear 502 ', and this is attached to a reflection type photo interrupter (phase). The rotation phase signal of each drive gear 502 ′ may be detected by the detection means). In this case, the rotation phase signal is generally shorter in the thrust direction of the drum drive coupling than the transmission type photo interrupter 508. The reflection type photo interrupter can make the image station compact.

  In the above embodiment, the protrusions 504-1, 504-2, and 504-3 project outward in the radial direction at three predetermined intervals in the circumferential direction on the outer peripheral surface of the drum drive coupling 501 of the drive gear 502. And recesses 504-4, 504-5, and 504-6 that are recessed radially outward at three circumferentially spaced intervals on the inner peripheral surface of the rear flange 32 of the photosensitive drum 3. Although the portion 504 is configured, any number of fitting portions may be provided as long as there are one or more fitting portions in the circumferential direction.

  In the above embodiment, the photosensitive drum 3a of the image station whose toner color is set to black is driven by one drum drive motor 503-1, and the toner color is cyan and magenta by the other drum drive motor 503-2. The photosensitive drums 3b to 3d of the image station set to yellow are driven, but the photosensitive drums of the image stations set to toner colors cyan, magenta, and yellow are respectively driven by individual drum drive motors. You may make it make it. In this case, the photosensitive drum of each image station is driven individually by four drum drive motors.

  In the above-described embodiment, the resin drive gear 502 (502a to 502d) is used as the drive means, but it is needless to say that a resin pulley may be applied as the drive means.

  Furthermore, in the above embodiment, the case where the present invention is applied to an image forming apparatus configured as a color printer has been described. However, the present invention is not limited to this, and an image forming apparatus configured as a color copying machine, The present invention can also be applied to an image forming apparatus configured as a multifunction machine having a function.

1 is a diagram illustrating an internal configuration of an image forming apparatus according to an embodiment of the present invention. It is a partially cutaway cross-sectional view showing the structure of a photosensitive drum and a drive gear. FIG. 5 is a perspective view of a photosensitive drum and a drive gear for explaining a configuration of a fitting portion. 2 is a schematic explanatory diagram illustrating a configuration of a drive mechanism of the image forming apparatus. FIG. (A) is explanatory drawing in the unfitted state of the fitting part which looked at the rear flange of a photoconductive drum and the drum drive coupling of a drive gear from the side orthogonal to the axial direction and the axial direction. ) Is an explanatory view of the rear flange of the photosensitive drum and the drum drive coupling of the drive gear when viewed from the axial direction and from the side perpendicular to the axial direction, in a match state immediately before the fitting portion is fitted. FIG. 3B is an explanatory view of the rear portion of the photosensitive drum and the drum drive coupling of the drive gear in the fitting state of the fitting portion when viewed from the axial direction and the side perpendicular to the axial direction. It is the perspective view which looked at the drum drive gear from the photoconductive drum side. It is the perspective view which looked at the drum drive gear concerning the modification of embodiment from the photoconductive drum side.

Explanation of symbols

3 (3a to 3d) Photosensitive drum (image carrier)
31 Raw pipe 32 Rear flange (drive side flange)
33 Front flange (non-drive side flange)
34 Shaft shaft 501 Drum drive coupling (drive shaft)
502 (502a to 502d), 502 '
Drive gear (drive means)
502-1 Protrusion (Detected part)
502-2 Reflector (detected part)
503-1, 503-2
Drum drive motor (drive source)
504 Fitting part 507 Energizing spring (urging means)
508 Photo interrupter (phase detection means)
A Image forming apparatus

Claims (17)

An image forming apparatus comprising an image forming unit that develops image information formed on an image carrier into a visible image, and transferring the visible image on the image carrier of the image forming unit to an image forming medium In
The image carrier of the image forming unit is coaxially connected to the driving means via a driving shaft,
Between the image carrier of the image forming unit and the driving unit, the image carrier of the image forming unit and the driving unit are fitted so as to be immovable in the circumferential direction only at a single circumferential position on the drive shaft. An image forming apparatus having a fitting portion. A plurality of image forming units that develop image information formed on the image carrier into visible images are arranged in parallel in the transfer material moving direction, and the visible images on the image carrier of these image forming units are sequentially imaged. In an image forming apparatus adapted to transfer to a forming medium,
The image carrier of each of the image forming units is coaxially connected to the driving unit via a driving shaft,
Between the image carrier of each image forming unit and the driving unit, the image carrier and driving unit of each image forming unit cannot be moved in the circumferential direction only at a single circumferential position on the drive shaft. An image forming apparatus comprising a fitting portion to be fitted. In the image forming apparatus according to claim 1 or 2,
An image forming apparatus, wherein a photosensitive drum is applied as the image carrier. The image forming apparatus according to any one of claims 1 to 3, wherein:
The drive shaft is connected to the drive means so as to rotate integrally,
The image forming apparatus according to claim 1, wherein the fitting portion is configured to fit the driving shaft and a shaft shaft penetrating and supported at the center of the image carrier. In the image forming apparatus according to claim 1 or 2,
The fitting portion is provided at least in one circumferential direction on the drive shaft between the image carrier of the image forming unit and the drive unit, and the image carrier of the image forming unit and the drive unit are arranged in the drive axis direction. An image forming apparatus characterized in that it is formed in a key shape that allows relative movement. In the image forming apparatus according to claim 5,
The drive shaft is supported so as to be movable in the axial direction relative to the drive means,
An image forming apparatus characterized in that an urging means for urging the image bearing member in a direction in which the drive shaft is fitted is provided between the drive shaft and the drive means. The image forming apparatus according to any one of claims 2 to 6, wherein:
An image forming apparatus comprising at least two drive sources for driving drive means connected to image carriers of a plurality of image forming units. The image forming apparatus according to claim 7, wherein
The driving source is
A driving source for driving a driving unit connected to an image forming unit that develops image information into a visible image with a black developer;
It is provided with two drive sources that individually drive drive means connected to an image forming unit that develops image information into a visible image by a developer of each color different from black. Image forming apparatus. The image forming apparatus according to claim 7, wherein
The driving source is
A driving source for driving a driving unit connected to an image forming unit that develops image information into a visible image with a black developer;
It is provided with four of three driving sources that individually drive driving means connected to an image forming unit that develops image information into a visible image with a developer of other three colors different from black. An image forming apparatus. The image forming apparatus according to any one of claims 7 to 9, wherein
A detected portion for detecting a rotational phase provided in a driving unit of each image forming unit;
Phase detecting means for individually detecting the rotational phase of the driving means by each detected part; and
An image forming apparatus comprising: control means for controlling rotation of each drive source based on individual rotation phase signals of the drive means detected by each phase detection means. The image forming apparatus according to claim 10, wherein
An image forming apparatus, wherein a protrusion provided on a side surface of a driving unit is applied as the detected portion. The image forming apparatus according to claim 10, wherein
An image forming apparatus, wherein a reflection plate provided on a side surface of a driving unit is applied as the detected portion. The image forming apparatus according to claim 10, wherein
The control means has a predetermined rotation phase of the drive means that is rotated by the drive force from the other drive source based on the rotation phase of the drive means that is rotated by the drive force from the predetermined drive source among the plurality of drive sources. An image forming apparatus controlled to maintain a value. The image forming apparatus according to claim 2,
An image forming apparatus characterized in that resin gears or pulleys formed by injection molding are respectively applied as driving means for the plurality of image forming units. The image forming apparatus according to claim 14, wherein
An image forming apparatus characterized in that the resin gears or pulleys of all of the plurality of image forming units are formed by the same mold having only a single cavity formed by a die and a punch. In the image forming apparatus according to claim 3,
The photosensitive drum is
An element tube formed by applying a photoreceptor layer on the surface of a cylindrical aluminum alloy;
A drive side flange made of resin that is press-fitted into one end of the base tube and fitted to the drive means via a drive shaft;
An image forming apparatus comprising: a resin non-driving side flange that is press-fitted into the other end of the element tube and supported by the image forming apparatus main body. The image forming apparatus according to claim 16, wherein
While the resin drive side flanges of all of the plurality of image forming units are molded by the same mold having only a single cavity formed by a die and a punch,
The resin-made non-driving side flanges of all of the plurality of image forming units are formed by the same mold having only a single cavity formed by a die and a punch. .

Images