JP2006119597A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device capable of forming a high-quality image. <P>SOLUTION: The image forming device forms an electrostatic latent image on a photoconductor drum 1 by light exposure unit 4, forms a toner image by supplying toner to the electostatic latent image from a developing unit 5, transfers the toner image to a transfer material A by a transfer/electrifier unit 6, thereby forming an image, wherein the drum shaft 1a of the photoconductor drum 1 and the rotary shaft 2a of a drive motor 2 are coupled by a constant-velocity joint J, so that even if the drum shaft 1a and the rotary shaft 2a are not aligned or inclined relative to each other, it is possible to prevent shrinkage or expansion of any electrostatic latent image or an image transferred to the transfer material by rotating the photoconductor drum 1 at a constant speed. By forming the outer ring 11 and the cage 21 of the constant-velocity joint J from a synthetic resin, it is possible to eliminate the need for lubrication with grease. With this arrangement, the constant-velocity joint J can be easily assembled and disassembled by inserting the cage 21 into the outer ring 11 and pulling the cage out of the outer ring, and parts of the image forming device such as the photoconductor drum 31 can be easily replaced with new ones and the maintenance of the image forming device is facilitated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer (LBP).

  A charger, an exposure unit, a developing unit, and a transfer charger are provided around the outer periphery of the photosensitive drum that is rotated in one direction. After the entire outer periphery of the photosensitive drum is uniformly charged by the charger, image information is obtained by the exposure unit. Image light is exposed to form an electrostatic latent image, and toner is supplied from the developing unit to the electrostatic latent image to form a toner image. The toner image is transferred to the photosensitive drum at the same peripheral speed as the transfer charger. 2. Description of the Related Art Image forming apparatuses that transfer onto a transfer material conveyed at a speed are conventionally known.

  In a monochromatic image forming apparatus, an image is formed by a set of image forming units including a photosensitive drum, a charger, an exposure unit, a developing unit, and a transfer charger. On the other hand, in a full-color image forming apparatus, four sets of images are formed. The image forming units are arranged in tandem in the transfer material conveyance direction, and each image forming unit forms a toner image of each color of yellow, magenta, cyan, and black, and these toner images are transferred onto the transfer material to form a color. An image is formed.

  In single-color and full-color image forming apparatuses, an image is formed by the rotation of the photosensitive drum. Therefore, if there is uneven rotation speed during one rotation of the photosensitive drum, the electrostatic latent image on the photosensitive drum is exposed during exposure by the exposure unit. In addition to the expansion and contraction, the image expands and contracts when the toner image is transferred to the transfer material, and these cause an image unevenness and cannot form a high quality image. Therefore, it is necessary to always rotate the photosensitive drum at a constant speed.

  It is known that when a photosensitive drum is driven, a rotating shaft of a motor is directly connected to the drum shaft of the photosensitive drum, and the photosensitive drum is rotated by driving the motor. In this case, it is extremely difficult to arrange the drum shaft of the photosensitive drum and the rotation shaft of the motor on the same axis, and when the misalignment or inclination occurs between the drum shaft and the rotation shaft. The photosensitive drum cannot be rotated at a constant speed, and a high-quality image cannot be formed.

In order to solve such problems, in the image forming apparatus described in Patent Document 1, the drum shaft of the photosensitive drum and the rotating shaft of the motor are connected by a universal joint, and the exposure position of the photosensitive drum and the transfer are transferred. The position is set at a position of 180 °, and the expansion and contraction of the image due to uneven rotation speed of the photosensitive drum is offset by the expansion and contraction of the image at the exposure position on the photosensitive drum and the transfer position, thereby preventing the expansion and contraction of the image on the transfer material. I am doing so.
JP-A-5-341589

  By the way, in the image forming apparatus described in Patent Document 1, since the universal joint is an inconstant speed universal joint, the photosensitive drum cannot be rotated at a constant speed, and the exposure position of the photosensitive drum and the transfer position can be transferred. Even if the position is set to 180 °, the position of 180 ° is displaced due to assembly errors, the photosensitive drum tilt, or bending, and the image expansion and contraction cannot be completely canceled, and a high quality image is formed. Can not do it.

  In addition, the inconstant-velocity universal joint cannot be easily disassembled from the input side to the output side, so that there is a problem that replacement of parts such as a photosensitive drum takes time and maintenance is difficult.

  An object of the present invention is to provide an image forming apparatus that is easy to maintain so that a high-quality image can be formed by always rotating a photosensitive drum at a constant speed.

  In order to solve the above problems, a photosensitive drum, driving means for rotating the photosensitive drum, exposure means for forming an electrostatic latent image on the photosensitive drum, and an electrostatic latent image on the photosensitive drum. The image forming apparatus includes developing means for supplying toner to form a toner image and transfer means for transferring the toner image onto a transfer material conveyed at the same speed as the peripheral speed of the photosensitive drum, and driving the drum shaft of the photosensitive drum. In the image forming apparatus in which the drive shaft of the means is connected by a shaft joint, the shaft joint has an annular space having one end opened, and three shafts extend in the axial direction on at least one of an outer wall surface and an inner wall surface of the annular space. An outer ring formed with a track groove of 120 ° in the circumferential direction, a second shaft is provided at an end portion of the outer ring located on the opening end side of the outer ring, and Poke at the position corresponding to the track groove A constant velocity joint having a cage formed with a cage, and a ball that can be rolled along the track groove formed in an outer ring of the cage, the cage outer diameter of each pocket in the cage A configuration is adopted in which a retaining means for preventing the ball from dropping off is provided at the opening end on the side and the inner diameter side of the cage.

  As the retaining means, it is possible to use a plurality of protrusions formed on the inner surface of the opening end of the pocket at intervals in the circumferential direction.

  In the constant velocity joint, when a tapered surface having a large diameter end at the opening end of the outer wall surface and the inner wall surface in the annular space is provided at the opening end portion of each track groove, the cage is incorporated into the annular space of the outer ring. Sometimes, the ball is guided by the tapered surface, and when the outer ring and the cage are rotated relative to each other in the guided state, the ball is inserted into the track groove, and there may be a phase shift between the ball and the track groove. The constant velocity joint can be easily assembled.

  Further, in the constant velocity joint, by forming the outer ring as a synthetic resin molded product, the constant velocity joint can be made non-lubricated, and the operation sound during torque transmission can be reduced and reduced in weight.

  In this case, the cage is also made of a synthetic resin, so that the operation noise during torque transmission can be further reduced and the constant velocity joint can be further reduced in weight.

  When the cage is made of a synthetic resin molded product, the protruding portion becomes an undercut when the cage is molded. Therefore, if the protruding length of the protruding portion becomes longer than necessary, the protruding portion may be damaged when demolding after molding. If the ball is too short, the ball may fall off. For this reason, it is good to make the inscribed circle diameter of a protrusion part into the range of 70 to 99% of a ball diameter.

  Here, by using a synthetic resin that can be injection-molded as the synthetic resin, the outer ring and the cage can be easily molded. Further, by adopting the lubricating resin, it is possible to further improve the lubricity of the ball rolling surface, so that it is possible to obtain a constant velocity joint with a smaller operating noise.

  As described above, the drum shaft of the photosensitive drum and the drive shaft of the drive means are connected by a constant velocity joint, so that the drive shaft of the drive means and the drum shaft of the photosensitive drum may be misaligned or inclined with respect to each other. The photosensitive drum can be rotated at a constant speed without causing uneven speed.

  For this reason, it is possible to prevent the electrostatic latent image formed by the exposure means from expanding and contracting, and the image from expanding and contracting when the toner image on the photosensitive drum is transferred to the transfer material. An image can be formed.

  In addition, by providing a retaining means to prevent the ball from falling off at the open end of the pocket formed in the cage, it is possible to prevent the ball from falling off when the cage is pulled out, making the constant velocity joint extremely easy. Can be assembled and disassembled. Therefore, parts such as the photosensitive drum can be easily replaced, and an image forming apparatus with easy maintenance can be obtained.

  Furthermore, at least the outer ring of the constant velocity joint and cage can be made of synthetic resin, so that grease lubrication can be dispensed with. The constant velocity joint can be assembled and disassembled by inserting / removing the cage into / from the annular space. Further, since grease lubrication can be dispensed with, it is possible to eliminate the inconvenience that the transfer material is soiled due to leakage of grease.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a monochromatic image forming apparatus. This image forming apparatus has a photosensitive drum 1. The photosensitive drum 1 is rotated in a direction indicated by an arrow in FIG. 1 by a driving motor 2 as a driving unit shown in FIG. 2, and around the photosensitive drum 1, a charger 3, an exposure unit 4, and a developing unit as a developing unit. 5. A transfer charger 6 and a cleaning device 7 as transfer means are provided in order in the rotation direction of the photosensitive drum 1.

  In the image forming apparatus having the above-described configuration, the entire outer periphery of the photosensitive drum 1 is uniformly charged by the charger 3 when the photosensitive drum 1 rotates, and then the exposure unit 4 exposes the image light based on the image information to electrostatically. A latent image is formed, toner is supplied onto the electrostatic latent image from the developing device 5 to form a toner image, and the toner image is conveyed by the transfer charger 6 at the same speed as the peripheral speed of the photosensitive drum 1. The image is transferred onto the transfer material A and an image is formed on the transfer material A. Further, after the transfer, the residual toner remaining on the peripheral surface of the photosensitive drum 1 is removed by the cleaning device 7.

  As shown in FIG. 2, the photosensitive drum 1 has drum shafts 1 a at both ends, and the drum shaft 1 a is rotatably supported by a pair of side frames 8 via bearings 9, while rotating the photosensitive drum 1. The driving motor 2 to be driven is attached to the casing 10 and arranged to face the photosensitive drum 1 in the axial direction.

  A rotating shaft 2 a as a driving shaft of the driving motor 2 and a drum shaft 1 a of the photosensitive drum 1 are connected through a constant velocity joint J.

  As shown in FIGS. 3 and 4, the constant velocity joint J includes an outer ring 11, a cage 21 and a ball 31.

  The outer ring 11 has a cup portion 12 that is open at one end, and a first shaft 13 is provided at the closed end of the cup portion 12. Further, a guide shaft 14 is provided on the central axis in the cup portion 12, an annular space 15 is formed between the guide shaft 14 and the cup portion 12, and the cup portion 12 that forms the outer wall surface of the annular space 15 is formed. Three track grooves 16, 17 extending in the axial direction are provided on the outer peripheral surface of the guide shaft 14 that forms the inner peripheral surface and the inner wall surface of the annular space 15 at intervals of 120 ° in the circumferential direction.

  In the embodiment, the track grooves 16 and 17 are formed on the outer wall surface and the inner wall surface of the annular space 15, respectively. However, the track groove may be provided on one of the outer wall surface and the inner wall surface.

  The cage 21 is incorporated in the annular space 15 of the outer ring 11, and a second shaft 22 is integrally provided at an end portion of the annular space 15 located on the opening end side.

  The cage 21 is formed with pockets 23 corresponding to the three track grooves 16 and 17 of the outer ring 11, and the balls 31 are incorporated in the pockets 23. Each of the balls 31 can roll along the track grooves 16 and 17.

  The outer ring 11 and the cage 21 may be made of metal, or may be made of a synthetic resin molded product. When a synthetic resin molded product is used, grease lubrication is not required, and it is possible to achieve non-lubrication, a reduction in operation sound during torque transmission, and a reduction in weight. For this reason, in the embodiment, each of the outer ring 11 and the cage 21 is a synthetic resin molded product. However, at least the outer ring 11 of the outer ring 11 and the cage 21 may be a synthetic resin molded product. The synthetic resin is preferably a synthetic resin that can be injection-molded. Any resin that can be injection-molded may be a thermoplastic resin or a thermosetting resin.

  There are two types of resin that can be injection-molded: crystalline resin and non-crystalline resin. Either resin can be used, but non-crystalline resin has low toughness. Therefore, it is preferable to use a crystalline resin.

  Preferred synthetic resins include synthetic resins with high lubrication characteristics, such as polyacetal resins (POM), nylon resins, fluoroplastics such as PFA, FEP, and ETFE, injection moldable polyimide resins, and polyphenylene sulfide resins (PPS). And wholly aromatic polyester resins, polyetheretherketone resins (PEEK), polyamideimide resins, and the like.

  Each of these resins may be used alone or a polymer alloy in which two or more kinds are mixed. Or the polymer alloy which mix | blended said synthetic resin with the synthetic resin with low lubrication characteristics other than the above may be sufficient.

  Moreover, even a synthetic resin having low lubricating properties can be used by enhancing the lubricating properties by adding a solid lubricant or lubricating oil. Examples of the solid lubricant include polytetrafluoroethylene, graphite, and molybdenum disulfide.

  Further, glass fiber, carbon fiber, various mineral fibers (whiskers) may be added to the synthetic resin to increase the strength, or may be used in combination with a solid lubricant or the like.

  The most suitable materials for use are POM, nylon resin, PPS, PEEK. The nylon resin may be nylon 6, nylon 66, nylon 610, nylon 612, nylon 11, nylon 12, nylon 46, semi-aromatic nylon having an aromatic ring in the molecular chain, or the like. Since POM, nylon resin, and PPS are excellent in heat resistance and lubricity and relatively inexpensive, a constant velocity joint with excellent cost performance can be obtained. Moreover, PEEK is excellent in mechanical strength and lubricity even if a reinforcing material and a lubricant are not blended, so that a high-performance constant velocity joint can be obtained.

  Balls 31 such as bearing steel, stainless steel, ceramics, and synthetic resins can be used as balls 31, but stainless steel, ceramics, and synthetic resins are preferable because there is no need to worry about rust even without lubrication. A synthetic resin is particularly preferable because it is lighter and quieter.

  In FIG. 3, the cage 21 and the second shaft 22 are integrally formed of synthetic resin, but the second shaft 22 is formed of a metal such as ceramics, steel, stainless steel, or aluminum alloy, and the cage 21 is formed of synthetic resin. And may be coupled by a coupling means such as a bolt.

  In the outer ring 11, the cup portion 12 and the guide shaft 14 are integrally formed of synthetic resin. However, the guide shaft 14 is formed of ceramics, steel, stainless steel, aluminum alloy or the like and is coupled to the cup portion 12. It may be.

  As shown in FIG. 3 and FIG. 4, retaining means 24 for preventing the balls 31 from falling off is provided at the opening ends of the pockets 23 on the cage outer diameter side and the cage inner diameter side.

  The retaining means 24 includes a pair of projecting portions 25 provided at positions opposed to the inner periphery of the pocket 23. Since the projecting portions 25 are undercut when the cage 21 is molded, the length of the projecting portions 25 in the pocket radial direction is reduced. If the length is longer than necessary, the protruding portion 25 is damaged at the time of demolding after molding, and if it becomes too short, the balls 31 cannot be prevented from falling off.

  For this reason, the inscribed circle diameter d of the protrusion 25 is in the range of 70 to 99% of the ball diameter (ball diameter) D of the ball 31.

  In addition, the number of the protrusion parts 25 is arbitrary, and the cyclic | annular thing which continues in the circumferential direction may be sufficient. Further, the retaining means 24 is not limited to the protruding portion 25. For example, a retaining ring or an O-ring may be attached to the opening end of the pocket 23. Or you may make it cover the cage 21 with the cover in which the hole was formed according to the pocket 23.

  As shown in the embodiment, by connecting the drum shaft 1a of the photosensitive drum 1 and the rotating shaft 2a of the driving motor 2 by a constant velocity joint J, the drum shaft 1a of the photosensitive drum 1 and the rotating shaft 2a of the driving motor 2 are connected. Even if there is a misalignment or inclination, the photosensitive drum 1 can be rotated at a constant speed without causing uneven speed. For this reason, the electrostatic latent image formed on the photosensitive drum 1 by the exposure unit 4 is expanded or contracted, and the image is expanded or contracted when the toner image on the photosensitive drum 1 is transferred by the transfer charger 6. Can be prevented.

  Therefore, it is possible to form a high-quality image, and it is not necessary to provide the exposure means 4 and the transfer charger 6 at a position of 180 °, so that the degree of freedom in design can be increased.

  Further, by using the outer ring 11 and the cage 21 of the constant velocity joint J as a synthetic resin molded product, grease lubrication can be eliminated. For this reason, it is possible to eliminate the inconvenience that the transfer material A is soiled by the scattering of grease.

  Furthermore, in the constant velocity joint J, as described above, grease lubrication can be dispensed with. Therefore, it is necessary to take measures to prevent leakage of grease by closing the open end of the outer ring 11 by attaching a boot. Therefore, the constant velocity joint J can be assembled and disassembled by inserting / removing the cage 21 into / from the annular space 15 of the outer ring 11. Moreover, since the retaining means 24 is provided at the opening end of the pocket 23 in the cage 21, it is possible to prevent the ball 31 from falling off during disassembly, and the constant velocity joint J is assembled and disassembled very easily. be able to.

  Therefore, it is easy to replace parts such as the photosensitive drum 1, and an image forming apparatus with easy maintenance can be obtained.

  Here, as shown in FIGS. 3 and 5, in the annular space 15 at the opening end of the track groove 16 formed on the inner peripheral surface of the cup portion 12 and the track groove 17 formed on the outer peripheral surface of the guide shaft 14. If the tapered surfaces 18 and 19 having large diameter ends at the open ends of the outer wall surface and the inner wall surface are provided, the ball 31 is guided by the tapered surfaces 18 and 19 when the cage 21 is assembled into the cup portion 12. By rotating the outer ring 11 and the cage 21 relative to each other in this state, the ball 31 is inserted into the track grooves 16 and 17, and even when the track grooves 16 and 17 and the ball 31 are out of phase with each other. The constant velocity joint J can be easily assembled.

  The tapered surfaces 18 and 19 may be tapered surfaces having an axial center on the central axis of the outer ring 11 as shown in FIG. 5, or axially on the pitch circle of the ball 31 as shown in FIG. It may be a tapered surface.

  As shown in FIG. 5, taper surfaces 18 and 19 having an axial center are formed on the central axis of the outer ring 11, and a minute guide projection 20 is formed between adjacent taper surfaces 18 and 19, thereby providing directionality. The constant velocity joint can be assembled without considering the above.

  Like the constant velocity joint J shown in FIGS. 3 and 4, the outer ring 11 is formed of a synthetic resin, so that the preload can be applied to the ball 31 using the elasticity of the outer ring 11. Specifically, the ball 31 is preloaded by making the inner diameter between the track groove 16 formed on the inner periphery of the cup portion 12 and the track groove 17 formed on the outer periphery of the guide shaft 14 smaller than the ball diameter of the ball 31. Can be granted. As a result, it is possible to obtain a constant velocity joint J which is free from backlash in the circumferential direction and has an excellent constant velocity, and the photosensitive drum 1 can be more effectively rotated at a constant velocity by driving the drive motor 2.

  In FIG. 1, a single color image forming apparatus has been described as an example. However, when forming a full color image forming apparatus, four sets of the image forming apparatuses shown in FIG. A toner image is formed with toners of four colors of yellow, magenta, cyan, and black by these image forming apparatuses, arranged in tandem in the conveying direction of A, and these toner images are superimposed on the transfer material A to form a color image. Form.

Schematic showing an embodiment of an image forming apparatus according to the present invention FIG. 1 is a partially cutaway front view showing a driving portion of the photosensitive drum shown in FIG. Partial cutaway front view of constant velocity joint shown in FIG. Sectional view along line IV-IV in FIG. Sectional drawing along the VV line of FIG. Sectional view showing still another example of constant velocity joint

Explanation of symbols

1 Photosensitive drum 1a Drum shaft 2 Drive motor (drive means)
2a Rotating shaft (drive shaft)
3 Charger 4 Exposure means 5 Developer (development means)
6 Transfer charger (transfer means)
11 outer ring 15 annular space 16 track groove 17 track groove 18 taper surface 19 taper surface 21 cage 22 second shaft 23 pocket 24 retaining means 25 protrusion 31 ball J constant velocity joint

Claims (8)

  A photosensitive drum; drive means for rotating the photosensitive drum; exposure means for forming an electrostatic latent image on the photosensitive drum; and supplying toner to the electrostatic latent image on the photosensitive drum to form a toner image. Developing means, and transfer means for transferring the toner image onto a transfer material conveyed at the same speed as the peripheral speed of the photosensitive drum. The shaft shaft of the photosensitive drum and the drive shaft of the drive means are connected by a shaft coupling. In the connected image forming apparatus, the shaft coupling has an annular space with one end opened, and three track grooves extending in the axial direction on at least one of the outer wall surface and the inner wall surface of the annular space are 120 ° in the circumferential direction. An outer ring formed with a space of the outer ring, and a second shaft is provided at an end portion of the outer ring located on the opening end side of the outer ring, and a pocket is provided at a position corresponding to the track groove. Formed cage and A constant velocity joint having a ball that is rollable along the track groove formed in the outer ring by being incorporated in a pocket of the cage, and an open end portion of each pocket in the cage on the cage outer diameter side and the cage inner diameter side An image forming apparatus characterized by further comprising a retaining means for preventing the ball from falling off.   2. The image forming apparatus according to claim 1, wherein the retaining means comprises a plurality of protrusions formed on the inner surface of the opening end of the pocket at intervals in the circumferential direction.   3. The image forming apparatus according to claim 1, wherein a tapered surface having a large-diameter end at an opening end of the outer wall surface and the inner wall surface in the annular space is provided at an opening end portion of each track groove.   4. The image forming apparatus according to claim 1, wherein the outer ring is a synthetic resin molded product.   The image forming apparatus according to claim 1, wherein the cage is a synthetic resin molded product.   The image forming apparatus according to claim 4, wherein the synthetic resin is made of a synthetic resin that can be injection-molded.   The image forming apparatus according to claim 4, wherein the synthetic resin is a lubricating resin.   The image forming apparatus according to claim 5, wherein an inscribed circle diameter of the protruding portion is 70 to 99% of a ball diameter.

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