JP2007033895A - Photoreceptor drum drive transmission apparatus for electrophotographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving system capable of preventing the occurrence of unevenness in pitch in an image, due to vibrations caused by the meshing of gears being transmitted to a photoreceptor drum, to cause rotational variations of the photoreceptor drum, in a driving system for driving the photoreceptor drum of the electrophotographic apparatus. <P>SOLUTION: The photoreceptor drum drive transmission apparatus has oscillation level transmitted to the drum reduced, by attaching an elastic member to the gears and having a drum axis rotated via the elastic member. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a drive transmission device for a photosensitive drum used in an electrophotographic copying machine, a printer, or the like.

  In an electrophotographic apparatus typified by a copying machine, the surface of the photosensitive drum is uniformly charged, and an electrostatic latent image corresponding to the photosensitive drum original image is formed by image exposure, and then the electrostatic latent image is developed. A toner image is formed on the surface of the photosensitive drum, the toner image is transferred from the surface of the photosensitive drum onto a transfer material such as paper, and the transferred toner image is fixed by heat, pressure, or the like, thereby forming an image. .

  In the electrophotographic apparatus as described above, the quality of the printed image often becomes a problem. There are multiple image defect phenomena and causes, and countermeasures are taken for each. This proposal is related to a technique for dealing with the banding problem caused by the rotational fluctuation of the photosensitive drum. The banding problem is streaky density unevenness that occurs at a substantially constant interval in the direction perpendicular to the paper transport direction. This is caused by fluctuations in the exposure of the latent image process due to fluctuations in the rotation of the photosensitive drum. Depending on what happens. The cause of the rotational fluctuation of the photosensitive drum is mainly a transmission error caused by the meshing of the gear of the drive system that rotationally drives the photosensitive drum.

  Conventionally, rotation transmission errors caused by meshing have been reduced by improving the shape accuracy of the gear or increasing the gear tooth width.

  However, there is a limit in improving the accuracy of plastic molding gears generally used in image forming apparatuses such as copying machines and laser beam printers. Further, there is a drawback that the downsizing of the apparatus is hindered by widening the tooth width. In this proposal, the rotation transmission error generated by the meshing of the gear is suppressed without improving the gear shape accuracy and without increasing the tooth width, and the banding level is improved.

In addition, as an image defect countermeasure technique different from the banding problem, an excessive load torque is applied to the transfer roller by interposing an elastic member such as a torsion coil spring in the path for driving the transfer roller in the prior art Japanese Patent Laid-Open No. 2001-51523. In this case, the idea of not causing distortion in the transferred image is shown, but it differs from the proposed method in that it aims to improve image defects that occur in the transfer section, and the proposed image is an image during normal operation. In contrast to the purpose of improving defects, the prior document differs in that it is an effective mechanism only when an excessive load torque is applied to the transfer roller. There is.
JP 2001-051523 A

  In a drive system for driving a photosensitive drum of an electrophotographic apparatus, a drive system that prevents the occurrence of pitch unevenness on an image due to the vibration generated by the engagement of gears being transmitted to the photosensitive drum and causing the rotational fluctuation of the photosensitive drum is provided. To do.

  According to the present invention, in the driving device of an electrophotographic apparatus in which the rotational force generated by the motor is driven to rotate the photosensitive drum via the rotating shaft and the gear pair consisting of the driving side and the driven side, the rotational force of the driven side gear is A photosensitive drum drive transmission device of an electrophotographic apparatus is provided, wherein the photosensitive drum drive transmission device is transmitted to the rotation shaft via an elastic member disposed between the driven gear and the rotation shaft.

  According to this configuration, rotation transmission that is constantly generated during image formation due to gear meshing due to poor tooth shape accuracy of the gear driving the photosensitive drum, tooth deformation due to load torque, gear pair alignment error, etc. The error is absorbed and attenuated by the elastic member, thereby reducing the rotational fluctuation of the photosensitive drum and improving the banding level. In addition, the above-described effects can be obtained without increasing the gear tooth shape accuracy and enlarging the device by expanding the tooth width.

  FIG. 3 shows an electrophotographic color copier equipped with the photosensitive drum drive transmission device of the present invention. The configuration and operation will be described below.

  In FIG. 3, 1R denotes an image reading unit that reads image data from a document placed on a document reading table. An image output unit 1P forms an image on a recording medium (transfer material P) based on image data input from an external device or a network via an image reading unit 1R or an external interface (not shown).

  The image output unit 1P is roughly divided into an image forming unit 10 (four stations a, b, c, and d are arranged in parallel, and the configuration is the same), a paper feeding unit 20, an intermediate transfer unit 30, and a fixing unit. 40 and a control unit (not shown) (consisting of a control board 170, a motor drive board (not shown), an external interface (not shown), etc.).

  Further, each unit will be described in detail.

  The image forming unit 10 is configured as described below.

Reference numerals 11a, 11b, 11c, and 11d denote photosensitive drums as image carriers, which are pivotally supported at the centers and are driven to rotate in the direction of the arrows. The primary chargers 12a, 12b, 12c, 12d, the laser scanner devices 13a, 13b, 13c, 13d, the developing devices 14a, 14b, 14c are opposed to the outer peripheral surfaces of the photosensitive drums 11a, 11b, 11c, 11d in the rotational direction. , 14d are arranged. In the primary chargers 12a to 12d, charges of a uniform charge amount are given to the surfaces of the photosensitive drums 11a to 11d.
Next, the laser scanner devices 13a to 13d expose the photosensitive drums 11a to 11d with laser beams modulated according to the recording image signal, thereby forming electrostatic latent images thereon. Further, the electrostatic latent images are visualized by developing devices 14a to 14d that respectively store four color developers (toners) such as yellow (Y), magenta (M), cyan (C), and black (BK). .

  The visualized visible image is transferred to an intermediate transfer member (intermediate transfer belt 31). On the downstream side of the image transfer areas Ta, Tb, Tc, and Td, the toner remaining on the photosensitive drums 11a to 11d without being transferred to the transfer material by the cleaning devices 15a, 15b, 15c, and 15d is scraped off and the surface of the drum is Clean.

  Through the process described above, image formation is sequentially performed using yellow (Y), magenta (M), cyan (C), and black (BK) toners.

  The paper feed unit 20 includes cassettes 21a and 21b and a manual feed tray 27 for storing the recording material P, pickup rollers 22a, 22b and 26 for feeding the recording material P one by one from the cassette or the manual feed tray, and each pickup roller. A pair of paper feed rollers 23 and a paper feed guide 24 for conveying the recording material P sent out from the recording roller to the registration rollers, and for feeding the recording material P to the secondary transfer region Te in accordance with the image forming timing of the image forming unit. It consists of registration rollers 25a and 25b.

  Hereinafter, the intermediate transfer unit 30 will be described.

  The intermediate transfer belt 31 includes a driving roller 32 that transmits driving to the intermediate transfer belt 31, a tension roller 33 that applies appropriate tension to the intermediate transfer belt 31 by urging of a spring (not shown), and a secondary transfer region across the belt. It is wound around a driven roller 34 facing Te. Among these, a primary transfer plane A is formed between the driving roller 32 and the tension roller 33. The drive roller 32 is coated with rubber (urethane or chloroprene) having a thickness of several millimeters on the surface of the metal roller to prevent slippage with the belt. The drive roller 32 is rotationally driven by a pulse motor (not shown). Primary transfer blades 35 a to 35 d are arranged behind the intermediate transfer belt 31 in primary transfer regions Ta to Td where the photosensitive drums 11 a to 11 d and the intermediate transfer belt 31 face each other.

  A secondary transfer roller 36 is disposed so as to face the driven roller 34, and a secondary transfer region Te is formed by a nip with the intermediate transfer belt 31. The secondary transfer roller 36 is pressed with an appropriate pressure against the intermediate transfer member. A cleaning device 50 for cleaning the image forming surface of the intermediate transfer belt 31 is disposed on the intermediate transfer belt 31 and downstream of the secondary transfer region Te. The cleaning device 50 includes a cleaner blade 51 (as a material). And a waste toner box 52 for storing waste toner.

  The fixing unit 40 includes a fixing roller 41a having a heat source such as a halogen heater therein, a fixing roller 41b to which the roller is pressed (the fixing roller 41b may also have a heat source), and a nip of the roller pair. It comprises a guide 43 for guiding the transfer material P to the part, and an inner discharge roller 44 and an outer discharge roller 45 for further guiding the transfer material P discharged from the roller pair to the outside of the apparatus.

  The control unit includes a control board 170 for controlling the operation of the mechanism in each unit, a motor drive board (not shown), and the like.

  Next, a description will be added in accordance with the operation of the apparatus.

  When an image forming operation start signal is issued, first, the transfer material P is sent out one by one from the cassette 21a by the pickup roller 22a. The transfer material P is guided between the paper feed guides 24 by the paper feed roller pair 23 and is conveyed to the registration rollers 25a and 25b. At that time, the registration rollers 25a and 25b are stopped, and the leading edge of the paper hits the nip portion. Thereafter, the registration rollers 25a and 25b start rotating in accordance with the timing at which the image forming unit starts to form an image. The rotation timing is set so that the transfer material P and the toner image primary-transferred onto the intermediate transfer belt 31 from the image forming unit exactly coincide with each other in the secondary transfer region Te.

  On the other hand, in the image forming unit, when an image forming operation start signal is issued, a high voltage is applied to the toner image formed on the photosensitive drum 11d that is the most upstream in the rotation direction of the intermediate transfer belt 31 by the process described above. Further, primary transfer is performed on the intermediate transfer belt 31 in the primary transfer region Td by the primary transfer charger 35d. The primarily transferred toner image is conveyed to the next primary transfer region Tc. In this case, image formation is delayed by a time during which the toner image is conveyed between the image forming portions, and the next toner image is transferred with the resist aligned on the previous image. Thereafter, the same process is repeated, and eventually, four color toner images are primarily transferred onto the intermediate transfer belt 31.

  Thereafter, when the recording material P enters the secondary transfer region Te and contacts the intermediate transfer belt 31, a high voltage is applied to the secondary transfer roller 36 in accordance with the passing timing of the recording material P. Then, the four color toner images formed on the intermediate transfer belt 31 by the process described above are transferred onto the surface of the recording material P. Thereafter, the recording material P is accurately guided to the fixing roller nip portion by the conveyance guide 43. The toner image is fixed on the surface of the recording material by the heat of the pair of fixing rollers 41a and 41b and the pressure of the nip. Thereafter, the recording material P is conveyed by the inner and outer discharge rollers 44 and 45, and the recording material P is discharged outside the apparatus.

  When obtaining a monochromatic image, a monochromatic visible image is primarily transferred onto the intermediate transfer member from a specific image forming unit (for example, the image forming unit d located at the most downstream in the traveling direction of the intermediate transfer member). A monochromatic image is obtained through the same process as that for forming the image.

  FIG. 1 is a cross-sectional view of a photosensitive drum driving unit, which is a characteristic configuration of the present invention, as viewed from above, and FIG. 2 is a perspective view in which only main components are extracted. A SUS φ8 diameter drum shaft 80 is passed between the front side plate 71 and the rear side plate 72, and both ends thereof are rotatably supported by bearings 73 and 74. The photosensitive drum 11a is mounted on the drum shaft 80 and is pressed against the rotation prevention pin 82 by a nut 81 to thereby perform positioning in the thrust direction and rotation prevention in the rotation direction. A stepping motor 91 for rotating the photosensitive drum is screwed to a drive frame 90 made of galvanized steel sheet. A drive side gear 92 is carved on the motor output shaft and meshes with the driven side gear 93 with a predetermined backlash. In order to improve the meshing rate, the gear tooth type has a helical gear with a twist angle of 20 °. The driven gear 93 is a polyacetal molded gear having a basic wall thickness of 1.5 mm, and a ball bearing 94 is press-fitted into the center thereof. The tooth profile accuracy of the driven gear is given a general JGMA grade 2 as the accuracy of the gear used for the drum drive system in a copying machine or the like. The ball bearing 94 is fitted to the drum shaft 80 and is positioned in the thrust direction by two E-rings 95. A cylindrical small protrusion 93a having a diameter of φ3.2 is integrally formed on the thinned disc portion of the driven gear 93, and a cylindrical silicon rubber having a φ3 system inner diameter slightly smaller than the diameter of the cylinder. The elastic member 96 made of is attached. The hardness of the silicon rubber is Shore A70, and the elastic member 96 is held by the small protrusion 93a by its own elastic force and does not fall off. One end of the lever plate 97 made of galvanized steel plate is integrally fixed to the end of the drum shaft 80 with a screw, and the other end is bent in a U-shape in the direction perpendicular to the rotational direction of the driven gear, and in the same direction The outer peripheral surface of the rubber 96 is sandwiched between these surfaces. With the above configuration, the driving force generated by the motor is transmitted from the driving side gear 92 to the driven side gear 93, and the photosensitive drum rotates when the lever member 97 rotates the drum shaft 80 via the elastic member 96.

  In the meshing part of the drive side gear and the driven side gear, the conventional configuration shown in FIG. 8 is also shown in FIG. 8 due to insufficient gear tooth shape accuracy, tooth deformation due to load torque, misalignment of gears due to insufficient component accuracy, etc. Even in the configuration, a transmission error occurs. When this embodiment and the conventional example have the same tooth pattern accuracy, are assembled with the same alignment and are used with the same load torque, it is considered that the rotational fluctuation level of the driven gear is the same. In the conventional example, since the driven gear and the drum shaft are directly connected, the rotational fluctuation level of the driven gear is directly the rotational fluctuation level of the drum shaft and the photosensitive drum. However, in the proposed system, the rotational fluctuation of the driven gear is reduced. The elastic member is damped by buffering, and the fluctuation level of the drum shaft and the photosensitive drum is reduced.

  Next, experimental results of this embodiment and the conventional type will be shown.

  4 and 5 are graphs obtained by measuring the rotational fluctuation of the drum shaft during image printing in an actual machine using a rotary encoder and analyzing the frequency by FFT analysis. Since the gear meshing frequency in this experiment is 200 Hz, comparing the rotational fluctuations near 200 Hz, it can be seen that the rotational fluctuations of the drum shaft are greatly improved compared to the conventional type. .

  6 and 7 are graphs obtained by measuring density unevenness of an image sample printed with an actual machine and performing frequency analysis by FFT analysis. In the vicinity of the gear meshing frequency of 200 Hz, the conventional type has a clear peak, whereas in this embodiment, there is no peak and the banding level is improved even in the actual image.

  That is, according to the present proposal, without using a gear having a high-precision tooth shape or a gear having a wide tooth width, the rotational fluctuation generated at the meshing portion of the gear is attenuated by the elastic member attached to the driven gear. Further, it is possible to suppress the rotational fluctuation on the drum shaft and the photosensitive drum, and it is possible to reduce the banding level caused by the rotational fluctuation of the drum.

FIG. 3 is a partial top view of the copying machine according to the embodiment of the present invention. Partial perspective view of the same 1 is a main cross-sectional view of a copying machine according to an embodiment of the present invention. Frequency analysis graph of measurement result of drum shaft rotation fluctuation in the embodiment of the present invention Frequency analysis graph of drum shaft rotation fluctuation measurement results in the conventional system Frequency analysis graph of density unevenness of image sample printed in an embodiment of the present invention Frequency analysis graph of density unevenness of image sample printed with conventional system Illustration of conventional example

Claims (2)

  In a driving apparatus of an electrophotographic apparatus in which a rotational force generated by a motor is driven to rotate a photosensitive drum through a pair of gears including a driving side and a driven side and a rotating shaft, the rotational force of the driven side gear and the driven side gear A photosensitive drum drive transmission device of an electrophotographic apparatus, wherein the photosensitive drum drive transmission device is transmitted to the rotation shaft through an elastic member disposed between the rotation shafts.   2. The driven elastic gear according to claim 1, wherein the driven gear is rotatably fitted to the rotating shaft, has a protruding portion provided on a disk portion of the driven gear, and the cylindrical elastic member attached to the protruding portion is itself A photosensitive drum drive transmission device for an electrophotographic apparatus, characterized in that a lever member held by elastic deformation and fixed to a rotating shaft abuts on the outer peripheral surface of the elastic member on a surface orthogonal to the rotation direction of the gear.

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