JP2005099235A - Rotary driving unit of photoreceptor drum - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rotary driving unit permitting the formation of a proper record image, in an image forming apparatus, by enhancing the precision regarding the rotational central position and the rotational velocity of a photoreceptor drum, and to provide the rotary driving unit capable of achieving such an objective inexpensively. <P>SOLUTION: The rotary driving unit is composed of: a unit housing fixed to an apparatus frame of the image forming apparatus; a driving motor fixed to the unit housing; a planetary reduction mechanism housed in the unit housing, having an output shaft disposed on the same axial center as the driving motor, and transmitting the rotation of the driving motor to the photoreceptor drum; a support housing provided so as to protrude from the unit housing and positioned with respect to the apparatus frame; and a drum shaft continuously formed with the output shaft of the planetary reduction mechanism, inserted into the photoreceptor drum through the support housing, and driving the photoreceptor drum. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a rotational drive unit for rotationally driving a photosensitive drum which is the center of an image forming operation in an image forming apparatus such as a copying machine or a laser beam printer. The present invention relates to an improvement for increasing positional accuracy and rotational accuracy.

JP 2000-346144 A JP 2002-171721 A JP-A-5-53381 Japanese Patent Laid-Open No. 5-180290

  In an image forming apparatus such as a copying machine or a laser beam printer, a toner image corresponding to image information is formed on a photosensitive drum rotating at a predetermined process speed, and the toner image is transferred and fixed on a recording sheet for recording. I have an image. Accordingly, if there is speed variation or eccentricity in the rotation of the photosensitive drum, a toner image faithful to the image information cannot be formed on the photosensitive drum. In particular, in full-color copying machines and full-color laser beam printers, it is required to superimpose yellow, cyan, magenta, and black toner images with high accuracy, and it is necessary to control the rotation of the photosensitive drum with high accuracy. Has been.

  On the other hand, the photosensitive drum is a consumable product because the photosensitive layer on the surface is worn away over time, and needs to be replaced according to the cumulative print amount. The apparatus frame is configured to be detachable from the apparatus frame, and is coupled to a driving mechanism such as a motor and a reduction gear train when the apparatus frame is mounted. That is, a coupling is provided at the tip of the rotating shaft of the photosensitive drum, and when the photosensitive drum is mounted so as to be pushed in the axial direction with respect to the apparatus frame, the coupling is output from the reduction gear train. It is configured to engage with a coupling provided on the shaft and transmit a rotational driving force to the photosensitive drum (Japanese Patent Laid-Open No. 2000-346144, etc.).

  However, when the photosensitive drum is coupled to the output shaft of the drive mechanism through the coupling provided at the tip of the rotational shaft of the photosensitive drum in this way, the rotational center of the photosensitive drum is set to the output shaft. It is difficult to make it completely coincide with the center of rotation, and vibration and rotational speed unevenness are likely to occur with respect to the rotation of the photosensitive drum.

  Also, when the rotational speed of the motor is reduced by using a reduction gear train when the photosensitive drum is driven to rotate, due to the formation accuracy of each gear, the eccentricity with respect to the rotating shaft, etc. Vibrations with a frequency corresponding to the rotation speed are likely to occur. For this reason, when the rotational speed of the motor is transmitted to the photosensitive drum via the reduction gear, even if the rotational speed of the motor is controlled with high accuracy, the rotational speed unevenness occurs on the photosensitive drum, which has a strict meaning. Then, there is a concern that color misregistration and color unevenness cannot be completely prevented.

  Therefore, in recent years, a traction type planetary reduction device has been proposed as a device that reduces the rotation of a motor without using a gear (Japanese Patent Laid-Open No. 2002-171721). In this planetary reduction device of the traction type, an internal ring is arranged so as to surround the sun roller connected to the output shaft of the motor, and between the inner peripheral surface of the internal ring and the outer peripheral surface of the sun roller. A plurality of planetary rollers are sandwiched between them, and an output shaft that is disposed on the same axis as the sun roller and rotates by the revolution of the planetary rollers is provided. With such a configuration, when the sun roller rotates with the rotation of the motor, the planetary roller rotates due to the frictional force acting between the sun roller and the planetary roller, and the planetary roller rotates while the sun roller rotates. Revolve around. The revolution causes the output shaft to rotate, and the rotation of the motor is transmitted to the output shaft in a decelerated state.

  As a drive mechanism of a photosensitive drum using this traction type planetary reduction device, those disclosed in Japanese Patent Laid-Open Nos. 5-53381 and 5-180290 are known. In this drive mechanism, a motor and the planetary speed reducer are built in the photosensitive drum, and the output shaft of the planetary speed reducer is directly the rotating shaft of the photosensitive drum. Therefore, when transmitting the rotation of the motor to the photosensitive drum, it is not necessary to use the coupling as described above, and it is possible to rotate the photosensitive drum with high precision. Since the motor and the planetary speed reducer are also replaced at the time of replacement, there is a problem that the running cost of the image forming apparatus, that is, the production cost per print increases.

  The present invention has been made in view of such problems, and an object of the present invention is to improve the accuracy with respect to the rotational center position and rotational speed of the photosensitive drum, thereby forming a good recorded image in the image forming apparatus. Another object of the present invention is to provide a rotary drive unit for enabling the above-mentioned purpose, and further to provide a rotary drive unit capable of achieving such an object at a low cost.

  That is, the present invention provides a rotary drive unit that rotates a photosensitive drum of an image forming apparatus, a unit housing fixed to an apparatus frame of the image forming apparatus, a drive motor fixed to the unit housing, A planetary speed reduction mechanism that is housed in a unit housing and has an output shaft disposed on the same axis as the drive motor, and that transmits the rotation of the drive motor to the photosensitive drum; and protrudes from the unit housing A support housing which is fitted and positioned in the apparatus frame, and an output shaft of the planetary speed reduction mechanism, and is formed continuously through the support housing and supported for rotation in the support housing. And a drum shaft that is inserted into the drum and drives the photosensitive drum. It is an.

  According to the rotary drive unit of the present invention configured as described above, the drum shaft formed continuously with the output shaft of the planetary reduction gear, in other words, the drum shaft extending the output shaft is inserted into the photosensitive drum. In addition, since the photosensitive drum is driven to rotate, the photosensitive drum is positioned on the same axis as the output shaft of the planetary reduction gear, and the output shaft is not decentered or uneven in rotational speed. . The drum shaft passes through a support housing protruding from the unit housing and is supported for rotation by the support housing. The support housing is fitted and positioned in the apparatus frame of the image forming apparatus. Therefore, the drum shaft itself is accurately positioned with respect to the apparatus frame. Further, the drum shaft is continuously formed from the output shaft of the planetary reduction mechanism in the unit housing, and is also supported for rotation in the support housing protruding from the unit housing. Even if the shaft length is extended to the extent that it is inserted, the bending can be sufficiently suppressed, and the rotational accuracy of the photosensitive drum can be increased with an inexpensive configuration.

  In such technical means, the planetary reduction mechanism may be of a type that transmits the rotational power of the motor to the output shaft by meshing the gear, but the meshing vibration of the gear propagates to the photosensitive drum. From the viewpoint of preventing this, it is preferable to use a so-called traction system that transmits the rotational power of the motor by the frictional force between the rollers.

  Further, if the drum shaft is inserted into the photosensitive drum and constitutes the rotational axis of the photosensitive drum, the photosensitive drum can be exposed without penetrating or penetrating the leading end of the drum shaft. It does not matter if it stays in the body drum. However, from the viewpoint of making the rotation center of the photosensitive drum completely coincide with the rotation center of the drum shaft, it is preferable that the drum shaft penetrates the photosensitive drum.

  Furthermore, since the drum shaft of the present invention is continuously formed from the output shaft of the planetary speed reduction mechanism and inserted into the photosensitive drum, the drum shaft has a considerable length. From the viewpoint of holding and improving the rotational accuracy of the photosensitive drum, it is preferable to provide a pair of bearings at a distance from each other in the support housing and the unit housing, and to support the rotation of the drum shaft by the bearings.

  Furthermore, in order to accurately rotate the photosensitive drum at a predetermined speed, an encoder that outputs a signal corresponding to the number of rotations of the drum shaft is used to grasp the actual rotation speed of the drum shaft and drive it. It is preferable to feedback control the rotational speed of the motor. At this time, from the viewpoint of accurately detecting the actual rotation speed of the drum shaft, the encoder is preferably provided at a position where the eccentricity of the drum shaft is as small as possible. In the present invention, the rotation of the drum shaft is performed. It is preferably provided between a pair of bearings that are supported.

  In a so-called tandem type color image forming apparatus provided with a photosensitive drum for each color of yellow, cyan, magenta, and black, there is a slight error in the interval between the photosensitive drums of each color, and the formed color recording image Color misregistration occurs. Accordingly, it is extremely important to position the photosensitive drums of the respective colors with respect to the apparatus frame, that is, to improve the absolute position accuracy. From this viewpoint, in the present invention, one of the pair of bearings for supporting the drum shaft is It is preferable to overlap the support housing through which the drum shaft passes and the apparatus frame. With this configuration, the drum shaft itself can be positioned extremely accurately with respect to the apparatus frame, and the absolute positional accuracy of the photosensitive drum with respect to the apparatus frame through which the drum shaft passes can be improved. Become.

  Further, the rotary drive unit of the present invention can fix the unit housing to the apparatus frame via a fixing bracket, and the deformation of the drum shaft after mounting the photosensitive drum is reduced to reduce the photosensitive drum. From the standpoint of maintaining a high accuracy of rotation, it is preferable that the rigidity of the fixed bracket is set lower than the rigidity of the apparatus frame. If the rigidity of the fixed bracket is lower than the rigidity of the device frame, if a large load is applied to the tip of the drum shaft that penetrates the device frame, the fixed bracket will be deformed before the device frame is deformed. Without being bent, it is slightly tilted around the penetrating position of the apparatus frame, and the influence on the rotation accuracy of the drum shaft can be minimized.

  Furthermore, in forming a toner image corresponding to image information on the photosensitive drum, it is necessary to develop the electrostatic latent image formed on the photosensitive drum by exposure with a developing device. Has a developing roll for adhering the toner to the photosensitive drum. In order to develop the electrostatic latent image with high quality toner, it is necessary to dispose the developing roll at a predetermined interval from the photosensitive drum and to rotate the developing roll with high accuracy like the photosensitive drum. . Therefore, it is important that the drive mechanism for applying the rotational driving force to the developing roll is accurately positioned with respect to the rotation center of the photosensitive drum. From this point of view, it is preferable to provide a reference surface for positioning the drive mechanism of the developing device with respect to the drum shaft in the support housing in the rotary drive unit of the present invention. That is, as described above, the sahort housing is positioned with respect to the apparatus frame of the image forming apparatus, and this determines the absolute position of the drum shaft, which is the rotation center of the photosensitive drum, with respect to the apparatus frame. If a reference surface for positioning the drive mechanism is provided on the support housing, the developing device can be positioned with respect to the drum shaft and, consequently, the device frame, and the electrostatic latent image is developed by the developing device. The positional relationship between the photosensitive drum and the developing roll in the middle can be made accurate, and the electrostatic latent image can be developed with high quality toner.

  Then, according to the rotation drive unit of the present invention configured as described above, the absolute position accuracy and rotation accuracy of the photosensitive drum, which is the most important in improving the image quality of the recorded image in the image forming apparatus, can be increased. An image forming apparatus using this rotational drive unit for rotationally driving the photosensitive drum can form a high-quality recorded image.

Hereinafter, a rotary drive unit of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows a schematic configuration of a full-color laser beam printer using a rotary drive unit of the present invention for driving a photosensitive drum. This laser beam printer includes four image forming engines 10Y, 10M, 10C, and 10Bk that form toner images for each of yellow, magenta, cyan, and black, and the toner images are primarily transferred from the image forming engines. An intermediate transfer belt 20 is provided, and the toner image multiple-transferred to the intermediate transfer belt 20 is secondarily transferred to the recording sheet P to form a full color image.

  The intermediate transfer belt 20 is formed in an endless shape and is wound around three belt transporting rolls 21 to 23 including a driving roll 21, and each color image forming engine 10Y, 10M, while rotating in the direction of the arrow. It is configured to receive a primary transfer of a toner image formed with 10C and 10Bk. Further, a secondary transfer roll 30 is disposed at a position facing the belt conveying roll 23 with the intermediate transfer belt 20 interposed therebetween, and the recording sheet P is interposed between the transfer roll 30 and the intermediate transfer belt 20 that are pressed against each other. The toner image is secondarily transferred from the intermediate transfer belt 20 by being inserted. That is, the belt conveyance roll 23 functions as a backup roll for the transfer roll 30, and the transfer roll 30 and the belt conveyance roll 23 constitute a secondary transfer unit.

  The intermediate transfer belt 20 is stretched between three belt conveyance rolls 21 to 23, and a substantially horizontal image receiving span is formed between the belt conveyance rolls 21 and 22, while the two are directly below the image receiving span. A third belt conveyance roll 23 facing the next transfer roll 30 is disposed and stretched in an inverted triangular shape as a whole.

  The four image forming engines 10Y, 10M, 10C, and 10Bk described above are arranged in parallel on the image receiving span of the intermediate transfer belt 20, and a toner image formed according to image information of each color is intermediate transferred. Primary transfer is performed on the belt 20. These four image forming engines 10Y, 10M, 10C, and 10Bk are arranged in the order of yellow 10Y, magenta 10M, cyan 10C, and black 10Bk along the rotation direction of the intermediate transfer belt 20, and are used most frequently. The black image forming engine 10Bk that is likely to be located is disposed closest to the secondary transfer portion. Each of the image forming engines 10Y, 10M, 10C, and 10Bk includes a raster scanning unit 12 that exposes the photosensitive drum 11 provided in each image forming engine in accordance with the image information. The laser beam Bm modulated accordingly exposes the photosensitive drums 11 of the image forming engines 10Y, 10M, 10C, and 10Bk.

  Each of the image forming engines 10Y, 10M, 10C, and 10Bk is sensitized by exposure of the photosensitive drum 11, the charger 13 that charges the photosensitive drum 11 to a uniform background portion potential, and the laser beam Bm. A developing device 14 that develops the electrostatic latent image formed on the photosensitive drum 11 to form a toner image, and residual toner and paper dust from the surface of the photosensitive drum 11 after the toner image is transferred to the intermediate transfer belt 20. A drum cleaner 15 that removes toner and a pre-cleaning static eliminator 16 that neutralizes residual toner prior to cleaning by the drum cleaner, and forms a toner image corresponding to image information of each color on the photosensitive drum 11. Configured to get.

  Primary transfer rolls 17Y, 17M, 17C, and 17Bk are disposed at positions facing the photosensitive drums 11 of the image forming engines 10Y, 10M, 10C, and 10Bk so as to sandwich the intermediate transfer belt 20, and these transfer rolls. By applying a predetermined transfer bias voltage to 17Y, 17M, 17C, and 17Bk, an electric field is formed between the photoconductive drum 11 and the transfer rolls 17Y, 17M, 17C, and 17Bk. The charged toner image is transferred to the intermediate transfer belt 20 by Coulomb force.

  Therefore, in forming a full color image by the color laser beam printer, first, the raster scanning unit 12 applies the photosensitive drums 11 of the image forming engines 10Y, 10M, 10C, and 10Bk at a predetermined timing according to the image information of each color. By exposure, a toner image corresponding to the image information is formed on each of the image forming engines 10Y, 10M, 10C, and 10Bk. The toner images formed by the image forming engines 10Y, 10M, 10C, and 10Bk are sequentially transferred to the rotating intermediate transfer belt 20, and a multiple toner image in which the respective color toner images are overlapped on the intermediate transfer belt 20. It is formed.

  On the other hand, after the recording sheet P is pulled out from the sheet cassette 40 one by one by the sheet feeding roll 41, the intermediate transfer belt 20 and the secondary transfer roll 30 pass through a predetermined sheet feeding path 46 indicated by a broken line in the drawing. Is fed to the secondary transfer portion in contact. A registration roll 42 is provided on the front side of the secondary transfer portion, and the recording sheet P is primary-transferred onto the intermediate transfer belt 20 by controlling the entry timing with respect to the secondary transfer portion by the registration roll 42. Registration with the toner image is performed.

  The backup roll 23 facing the secondary transfer roll 30 with the intermediate transfer belt 20 interposed therebetween is formed by covering the surface of the insulating roll with a semiconductive sheet, and a predetermined transfer bias voltage is applied to the surface. The conductive contact roll 50 is in contact. Accordingly, when a transfer bias voltage having the same polarity as that of the toner image is applied to the contact roll 50 and a charge is applied to the surface of the backup roll 23, the transfer roll 30 and the intermediate transfer located on the back side of the recording sheet P are transferred. A transfer electric field is formed between the backup roll 23 located on the back side of the belt 20, and the toner image held on the intermediate transfer belt 20 is electrostatically transferred to the recording sheet P.

  The recording sheet P on which the toner image has been secondarily transferred is peeled off from the intermediate transfer belt 20 and then conveyed to the fixing device 44 by a series of two sheet conveying belts 43 arranged in series. The recording sheet P is fixed on the toner image by the fixing device 44 and then discharged to the paper discharge tray 45, whereby the formation of the full color image on the recording sheet P is completed. Further, in this printer, an inverter passage 47 for inverting the front and back of the recording sheet P between the fixing device 44 and the discharge tray 45 in order to enable so-called face-down discharge with the image surface of the recording sheet P facing downward. Is formed. Further, the inverter passage 47 is connected to the above-described sheet feeding passage 46 by a sheet re-transmission passage 48. By feeding the recording sheet P that is reversed upside down in the inverter passage 47 to the secondary transfer portion again, the recording sheet P It is possible to form recorded images on both the front and back sides.

  In this color printer, in order to perform the transfer position alignment of each color toner image on the intermediate transfer belt 20 with high accuracy, the photosensitive drum 11 is driven for each of the image forming engines 10Y, 10M, 10C, and 10Bk as shown in FIG. Rotating drive unit 6 (6Y, 6M, 6C, 6Bk) is provided so that the rotational speeds of the photosensitive drums 11Y, 11M, 11C, 11Bk for yellow, magenta, cyan, and black can be individually controlled. It has become. 2 clearly shows the relationship between the rotary drive units 6Y, 6M, 6C, and 6Bk and the photosensitive drums 11Y, 11M, 11C, and 11Bk, and other devices that are originally provided around these units are omitted. It is drawn.

  FIG. 3 is a cross-sectional view showing each rotary drive unit 6. The rotational drive unit 6 penetrates the photosensitive drum 11 and drives the photosensitive drum 11, a driving motor M as a driving source, and rotation of the driving motor M at a predetermined reduction ratio. A planetary speed reduction mechanism 5 that decelerates and transmits to the drum shaft 60 is provided, and the photosensitive drum 11 is mounted on the drum shaft 60. The drive motor M is fixed to the outside of a unit housing 61 formed in a substantially rectangular shape, and the motor shaft 51 is inserted into the unit housing 61. In the unit housing 61, the planetary reduction mechanism 5 and Are combined.

  FIG. 4 shows an example of the planetary reduction mechanism 5. The planetary speed reduction mechanism in this figure is not a gear but a so-called traction type planetary speed reduction roller mechanism that transmits the rotation of the motor to the drum shaft by using the frictional force between the rollers. The planetary speed reduction roller mechanism 5 includes a sun roller 51 that can directly use the motor shaft of the motor M, a plurality of planetary rollers 52 arranged so as to be in contact with the outer peripheral surface of the sun roller 51, and the planetary rollers 52 outside. And an output ring 54 disposed on the same axial center as the sun roller 51, and fixed to the output shaft 54 and rotatable about the planetary roller 52. The output shaft 54 is supported on a housing 56 via a bearing, while the sun roller 51 is fixed to an end plate 57 via a bearing. Then, by fixing the end plate 57 to the housing 56, a housing space for the sun roller 51, the planetary roller 52, the internal ring 53, and the carrier 55 is formed in the housing 56, and the housing space is lubricated. Filled with grease as agent.

  Each planetary roller 52 has a large diameter portion 52a and a pair of small diameter portions 52b provided so as to sandwich the large diameter portion 52a from both sides in the axial direction. The former large diameter portion 52a has an outer peripheral surface thereof. Is in pressure contact with the outer peripheral surface of the sun roller 51. Each small diameter portion 52 b of the planetary roller 52 is formed in a tapered shape, and the outer peripheral surface of the small diameter portion 52 b is in pressure contact with the inner peripheral surface of the internal ring 53. These planetary rollers 52 are rotatably supported by a rod 58 standing on the carrier 55, and are rotated along with the rotation of the sun roller 51 with the rod 58 as a rotation center.

  On the other hand, the internal ring 53 is composed of a fixed ring 53a and a movable ring 53b, and the inner peripheral surface of each ring 53a, 53b is formed in a tapered shape that matches the outer peripheral surface of the small diameter portion of the planetary roller 52. . The movable ring 53 b and the fixed ring 53 a are arranged so as to sandwich the large diameter portion 52 a of the planetary roller 52 from the axial direction, and the fixed ring 53 a is fixed to the housing 56. The movable ring 53b is fixed to the housing 56 with respect to the circumferential direction thereof, but is disposed so as to be movable within the housing 56 with respect to the axial direction. Further, the movable ring 53b is pressed in the axial direction by a compression coil spring 59, and the movable ring 53b and the fixed ring 53a sandwich the small diameter portion 52b of the planetary roller 52 from both sides in the axial direction by the pressing force. The tapered inner peripheral surface and the tapered inner peripheral surface of the fixing ring 53a are configured to come into pressure contact with the tapered outer peripheral surface of the small diameter portion 52b of the planetary roller 52, respectively.

  The motor shaft of the motor M is connected to the sun roller 51 of the planetary reduction mechanism 5 configured as described above and rotates the sun roller 51. The output shaft of the motor M itself is inserted into the housing 56, and the sun roller 51. When the output shaft of the motor M, that is, the sun roller 51 is rotated, the planetary roller 52 pressed against the outer peripheral surface of the sun roller 51 is rotated along with the rotation of the sun roller 51. Since the small diameter portion 52b is in pressure contact with the internal ring 52 (movable ring 52b and fixed ring 52a) fixed in the circumferential direction, the planetary roller 52 revolves around the sun roller 51 while rotating. As a result, the carrier 55 supporting the planetary roller 52 rotates, and the output shaft 54 to which the carrier 55 is fixed rotates at the revolution speed of the planetary roller 52.

  As shown in FIG. 3, the drum shaft 60 is formed continuously and integrally with the output shaft 54 of the planetary reduction roller mechanism 5. That is, by extending the output shaft 54 of the planetary reduction mechanism 5 in the axial direction and penetrating the photosensitive drum 11, the output shaft 54 becomes the drum shaft 60 as it is.

  The unit housing 61 containing the planetary speed reduction roller mechanism 5 is fixed from the rear side to the printer apparatus frame F via a fixing bracket 62 made of a metal plate, and the drum shaft 60 protrudes from the unit housing 61 and is fixed to the fixing bracket 62. 62, and the apparatus frame F is penetrated from the rear side to the front side. Further, a substantially cylindrical support housing 63 projects from the unit housing 61 so as to cover the drum shaft 60, and the support housing 63 penetrates the fixed bracket 62, and its tip is attached to the apparatus frame F. The fitting hole 64 is provided. That is, the outer peripheral surface of the distal end portion of the support housing 63 formed in a cylindrical shape is a reference surface for positioning the rotary drive unit 6 with respect to the apparatus frame F.

  In addition, in order to reliably support the long drum shaft 60, a pair of bearings 65 and 66 are provided in the unit housing 61 and the support housing 63, and these bearings 65 and 66 are provided on the drum shaft 60. It is arranged at a certain distance in the axial direction. Of these bearings, one bearing 66 is provided at the distal end of the support housing 63, and when the support housing 63 is positioned by being fitted to the apparatus frame F, the bearing 66 is connected to the apparatus frame F. It is designed to be fixed at the overlapping position.

  As a result, each rotary drive unit 6 is positioned on the apparatus frame F with the outer peripheral surface of the support housing 63 as a reference plane, and the drum shaft 60 is rotated by a bearing 66 disposed at a position overlapping the apparatus frame F. Since it is supported with respect to the support housing 63, the absolute position accuracy of the drum shaft 60 with respect to the apparatus frame F becomes extremely high, and the absolute position accuracy with respect to the apparatus frame F of the photosensitive drum 11 through which the drum shaft 60 passes is also improved. It can be very high.

  In order to accurately control the rotational speed of the photosensitive drum 11, a rotary encoder 67 for detecting the rotational speed of the drum shaft 60 is built in the unit housing 61, and a detection signal of the rotary encoder 67 is received. The rotational speed of the drive motor M is used for feedback control. The rotary encoder 67 is provided between the pair of bearings 65 and 66 described above, and since the eccentricity of the drum shaft 60 is hardly recognized at such a position, the rotational speed of the drum shaft 60 can be accurately detected. It is possible.

  As shown in FIG. 2, the photosensitive drums 11 of the image forming engines 10Y, 10M, 10C, and 10Bk are attached to and detached from the drum shaft 60 in the axial direction. A key groove 60a is provided in the vicinity of the tip of the drum shaft 60. When the drum shaft 60 is inserted into the through hole of the photosensitive drum 11, the key (FIG. (Not shown) enters the key groove 60a, and the photosensitive drum 11 and the drum shaft 60 are coupled in the circumferential direction.

  Actually, the photosensitive drums 11 are not individually mounted on the drum shaft 60, but the drums corresponding to the photosensitive drums 11 are simultaneously pressed by pushing the holding frame 7 shown in FIG. 5 into the apparatus housing of the printer. Mounted on the shaft 60. Although FIG. 5 is drawn with the photosensitive drum 11 omitted, the shaft ends of the photosensitive drums 11 are temporarily held with some play with respect to the rear plate 70 and the front plate 71 of the holding frame 7. When the holding frame 7 is pushed into the printer casing along the direction of the arrow in the figure, the drum shaft 60 of the rotation drive unit 6 is inserted into the through hole of each photosensitive drum 11 and the photosensitive drum. 11 is positioned around the drum shaft 60. Further, when the holding frame body 7 is completely pushed into the printer casing, the stud 72 standing on the rear plate 70 of the holding frame body 7 is fitted into the apparatus frame F to which the rotary drive unit 6 is fixed. In addition to positioning the holding frame body 7 with respect to the apparatus frame F, the leading end of each drum shaft 60 is fitted into a bearing 73 provided on the front plate 71 of the holding frame body, and the leading end of the drum shaft 60 is It is supported by the holding frame 7. As a result, when the holding frame 7 is pushed into the printer housing, the photosensitive drum 11 is positioned around the drum shaft 60 positioned with high accuracy with respect to the apparatus frame F, and the four The distance and parallelism between the photosensitive drums 11Y, 11M, 11C, and 11Bk can be ensured. Further, the holding frame 7 also holds a developing device 14 and a drum cleaner 15 that constitute the image forming engines 10Y, 10M, 10C, and 10Bk, which are combined with the photosensitive drums 11Y, 11M, 11C, and 11Bk. Can be positioned.

  Of the four rotary drive units 6Y, 6M, 6C, and 6Bk corresponding to each color, the rotary drive unit 6Bk corresponding to black is fixed independently to the apparatus frame F, but the other yellow, magenta, and cyan The three rotary drive units 6Y, 6M, and 6C corresponding to the above are fixed to the apparatus frame F by one fixing bracket 62, and as shown in FIG. 6, drive modules corresponding to three colors of yellow, magenta, and cyan 8 is constituted. The drive module 8 includes a driving mechanism for driving the developing device 14 and the drum cleaner 15 included in the yellow, magenta, and cyan image forming engines 10Y, 10M, and 10C. A driving force is distributed from one process motor 80 to the drum cleaner 15. In other words, the yellow, magenta and cyan developing units 14 and the drum cleaner 15 other than black are always driven together, and the black developing unit 14 and the drum cleaner 15 are at timings different from those colors. It is possible to drive. In the printer shown in this embodiment, since only the black image forming engine 10Bk can be driven separately from the other color image forming engines 10Y, 10M, and 10C, yellow, magenta, and cyan are formed when a monochrome image is formed. The photoconductor drums 11Y, 11M, and 11C, the developing device 14 and the drum cleaner 15 can be stopped, and the power consumption can be suppressed correspondingly, and the photoconductor drums 11Y, 11M for yellow, magenta, and cyan can be reduced. , 11C can be prevented from being worn.

  As shown in FIG. 6, the drive module 8 is configured to be sandwiched between a fixed bracket 62 and a middle plate 81, and when the fixed bracket 62 and the middle plate 81 are coupled, the middle Each drum shaft 60 protrudes from the plate 81, and a developer drive shaft 82 and a cleaner drive shaft 83 protrude adjacent to each drum shaft 60. The developing device driving shaft 82 and the cleaner driving shaft 83 are provided with gears or couplings at their tips. When the entire drive module 8 is fixed to the apparatus frame F, the drum shaft 60, the developing device driving shaft 82, and the cleaner driving shaft 83 are fixed. Protrudes to the front side of the apparatus frame F. Thus, when the holding frame 7 shown in FIG. 5 is pushed into the printer housing, the developing device drive shaft 82 and the cleaner drive shaft 83 with respect to the developing device 14 and the drum cleaner 15 held by the holding frame 7. Are connected to each other so that the power of the process motor 80 can be transmitted.

  The developer drive shaft 82 and the cleaner drive shaft 83 are supported on the middle plate 81 via bearings 84. Further, as shown in FIG. 3, the middle plate 81 is provided with positioning holes 85 into which the support housings 63 of the yellow, magenta, and cyan rotary drive units 6 are fitted. The rotary drive unit 6 is positioned with respect to the outer peripheral surface. As described above, since the outer peripheral surface of the support housing 63 is also used as a positioning reference for each rotation drive unit 6 with respect to the device frame F, the middle plate 81 is connected to the device frame F via the support housing 63 of the rotation drive unit 6. Will be positioned accurately. Therefore, the developing device drive shaft 82 and the cleaner drive shaft 83 supported on the middle plate 81 via the bearings 84 are accurately positioned with respect to the apparatus frame F and consequently the drum shaft 60. As a result, the positional relationship between the photosensitive drum 11 and the developing roller of the developing device 14 and the positional relationship between the photosensitive drum 11 and the drum cleaner 15 can be accurately maintained, and the electrostatic latent image on the photosensitive drum 11 can be maintained. It is possible to develop the toner with the developing device 14 satisfactorily.

  The plate thickness of the fixed bracket 62 constituting the drive module 8 is set to 0.5 mm, and the rigidity is lower than the plate thickness of the device frame F of 1.6 mm. For this reason, for example, when the drum cleaner 15 is pressed against the photosensitive drum 11 and a radial load is applied to the drum shaft 60, the fixed bracket 62 is deformed before the drum shaft 60 is bent. The drum shaft 60 is slightly inclined with the penetration position of the device frame F as the center. As a result, even when a radial load is applied to the drum shaft 60, fluctuations in the rotational speed of the drum shaft 60, that is, fluctuations in the rotational speed of the photosensitive drum 11 can be suppressed.

  FIG. 7 shows the results of examining how much the rotational speed V of the drum shaft 60 fluctuated before and after the radial displacement was given to the tip of the drum shaft 60. The rotary drive unit 6 was fixed to the apparatus frame F via a fixed bracket 62. The fixed bracket 62 used was a plate having a thickness of 0.5 mm and a plate having a thickness of 2 mm. The thickness of the apparatus frame F to which the fixing bracket 62 is attached is 1.6 mm. The horizontal axis of the graph shown in FIG. 7 indicates the amount of displacement in the radial direction at the tip of the drum shaft 60, and the vertical axis indicates the variation rate of the rotational speed of the drum shaft 60. As shown in this graph, as the amount of displacement in the radial direction at the tip of the drum shaft 60 increases, the fluctuation rate of the rotational speed of the drum shaft 60 increases. In addition, when the fixing bracket 62 having a thickness of 2 mm is attached to the apparatus frame F having a thickness of 1.6 mm, the speed of the drum shaft 60 is increased even if the displacement amount of the tip of the drum shaft 60 is about 1.0 mm. Although the fluctuation exceeded 0.05%, when the fixing bracket 62 with a plate thickness of 0.5 mm was attached to the device frame F with a plate thickness of 1.6 mm, the tip of the drum shaft 60 was displaced to the same extent. Even if it was made, the fluctuation rate of the rotational speed of the drum shaft 60 did not increase. Accordingly, it has been found that the rate of change in the rotational speed of the drum shaft 60 can be reduced when the rigidity of the fixed bracket 62 is set to be lower than the rigidity of at least the device frame F.

  Next, FIG. 6 is a block diagram showing a control system for the rotational speed of the photosensitive drum 11 when such a rotational drive unit 6 is used. A configuration surrounded by a broken line in the drawing is a drive control device provided for each color photosensitive drum 11Y, 11M, 11C, 11Bk, and each drive control device is connected to the main control board 9 of the image forming apparatus. A signal relating to the rotational speed of the photosensitive drum 11 is transmitted and received. The drive control device includes a rotation control unit 90 configured by a computer system, and the rotation control unit 90 sends a drive control signal to the drive motor M of the photosensitive drum 11.

  The planetary reduction device 5 of the traction type (friction transmission type) has characteristics such as less fluctuation in angular velocity, low noise, and low vibration compared with a reduction device using gears. Above all, since gear meshing vibration does not occur, there is an advantage that striped image quality defects called banding are unlikely to occur in a recorded image. On the other hand, the rotational torque is not transmitted by the meshing of the gears, but the rotational torque is transmitted by the frictional force between the rollers that are in pressure contact with each other. There is a characteristic that a slip occurs between the rotation speeds of the drive motor and the output speed of the planetary reduction roller mechanism, that is, the rotation speed of the drum shaft does not correspond one-to-one.

  From this, the rotation control unit 90 reads the detection signal of the rotary encoder 67 described above, thereby grasping the rotation speed of the drum shaft 60, that is, the rotation speed of the photosensitive drum 11. The rotation control unit 90 compares the rotation speed of the drum shaft 60 with the target rotation speed of the photosensitive drum 11 instructed from the main control board 9 of the image forming apparatus, and the rotation speed of the drum shaft 60 is the target rotation speed. The rotation of the drive motor M is feedback controlled so that Thereby, the rotation of the photosensitive drum 11 can be controlled to an optimum speed for each of the image forming engines 10Y, 10M, 10C, and 10Bk.

  The rotation control unit 90 can be provided for each color rotation drive unit. However, when a monochrome image is printed as described above, the yellow, magenta, and cyan image forming engines 10Y, 10M, and 10C stop driving. When forming a color image, the yellow, magenta, and cyan image forming engines 10Y, 10M, and 10C are always driven together, so that they correspond to the yellow, magenta, and cyan image forming engines 10Y, 10M, and 10C. Regarding the rotation drive units 6Y, 6M, and 6C, it is preferable that the rotation control unit 90 is integrated into one, and the rotation control unit 90 is provided separately only for the rotation drive unit 6Bk corresponding to the black image forming engine 10Bk. With this configuration, it is possible to reduce the production cost by causing the number of parts constituting the control system to occur and reducing the routing of the signal lines.

FIG. 2 is a diagram showing a schematic configuration of a full-color laser beam printer that can use the rotation drive unit of the present invention for driving a photosensitive drum. It is a perspective view which shows the mounting state of the photosensitive drum with respect to the drum shaft of a rotation drive unit. It is sectional drawing which shows the state which attached the rotational drive unit of this invention to the apparatus frame. It is sectional drawing which shows the planetary reduction roller mechanism which can be used for the rotational drive unit of this invention. FIG. 6 is a perspective view showing a positional relationship between a holding frame body that temporarily holds a photosensitive drum and a drum shaft. It is a perspective view which shows a drive module. It is a graph which shows the relationship between the displacement amount of a drum shaft front-end | tip, and the speed fluctuation of this drum shaft. It is a block diagram which shows the control system for controlling the rotational speed of a drum shaft.

Explanation of symbols

  5 ... Planetary speed reduction roller mechanism, 6 (6Y, 6M, 6C, 6Bk) ... Rotation drive unit, 10 (10Y, 10M, 10C, 10Bk) ... Image forming engine, 11 (11Y, 11M, 11C, 11Bk) ... Photoconductor Drum, 60 ... drum shaft, 61 ... unit housing, 62 ... fixed bracket, 63 ... support housing, F ... device frame, M ... drive motor

Claims (8)

A rotational drive unit that rotates a photosensitive drum of an image forming apparatus,
A unit housing fixed to an apparatus frame of the image forming apparatus;
A drive motor fixed to the unit housing;
A planetary reduction mechanism having an output shaft housed in the unit housing and disposed on the same axis as the drive motor, and transmitting the rotation of the drive motor to the photosensitive drum;
A support housing that protrudes from the unit housing and is positioned by fitting into the device frame;
A drum shaft that is formed continuously with the output shaft of the planetary speed reduction mechanism, passes through the support housing and is supported for rotation in the support housing, and is inserted into the photosensitive drum to drive the photosensitive drum;
A rotary drive unit comprising: 2. The rotary drive unit according to claim 1, wherein a tip of the drive shaft penetrates the photosensitive drum and is supported by a temporary holding frame body of the photosensitive drum. 2. The rotary drive unit according to claim 1, wherein the rotation of the drum shaft is supported by a pair of bearings provided at a distance from each other in the support housing and the unit housing. 4. The rotary drive unit according to claim 3, wherein an encoder that outputs a signal corresponding to the number of rotations of the drum shaft is provided between a pair of bearings that support the rotation of the drum shaft. 4. The rotary drive unit according to claim 3, wherein at least one of the bearings is provided so as to overlap with a fitting position between the device frame and the support housing. 6. The rotary drive unit according to claim 5, wherein the unit housing is fixed to the apparatus frame via a fixing bracket, and the rigidity of the fixing bracket is set lower than the rigidity of the apparatus frame. 2. The rotary drive unit according to claim 1, wherein the support housing is provided with a reference surface for positioning a drive mechanism of a developing device with respect to the drum shaft. In a color image forming apparatus including a plurality of photosensitive drums on which toner images corresponding to image information are formed, and forming a recorded image by superimposing the toner images formed on the photosensitive drums,
A color image forming apparatus using the rotation drive unit according to claim 1 for rotation of each photosensitive drum.

Images