JP4711755B2 - Image forming apparatus - Google Patents

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 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. It is extremely difficult to place the drum shaft of the photosensitive drum and the rotation shaft of the motor on the same axis because of an error at the time, and a misalignment or inclination occurs between the drum shaft and the rotation shaft. 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 180 ° position may be displaced due to assembly errors, the photosensitive drum tilt, or bend, and the expansion and contraction of the image cannot be completely cancelled. Can not do it.

  An object of the present invention is to provide an image forming apparatus capable of forming a high-quality image by always rotating a photosensitive drum at a constant speed.

  In order to solve the above-described problems, in the present invention, a photosensitive drum, a driving unit that rotationally drives the photosensitive drum, an exposure unit that forms an electrostatic latent image on the photosensitive drum, and a photosensitive drum The photosensitive drum comprises: developing means for supplying toner to the electrostatic latent image 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. In the image forming apparatus in which the drum shaft and the drive shaft of the drive means are connected by a shaft joint, the shaft joint has an annular space with one end opened, and the shaft is attached to at least one of the outer wall surface and the inner wall surface of the annular space. An outer ring formed with three track grooves extending in the circumferential direction at an interval of 120 ° in the circumferential direction, and the second shaft is incorporated in the annular space of the outer ring and at the end located on the opening end side of the outer ring Cage provided and its Held in the over-di it had adopted a configuration using a constant velocity joint having a rollable ball along the track groove formed in the outer ring.

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

  In addition, by making the constant velocity joint cage a synthetic resin molded product, it is possible to further reduce the operation noise during torque transmission of the constant velocity joint and to reduce the weight of the constant velocity joint. Can do.

  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.

  Furthermore, by applying a preload to the balls of the constant velocity joint, it is possible to obtain a constant velocity joint that is free of circumferential play and is excellent in constant velocity. Can be rotated.

  In addition, by dividing the outer ring of the constant velocity joint between adjacent track grooves and forming three elastic pieces having track grooves, when excessive torque is applied to the constant velocity joint, each elastic piece It is possible to block the transmission of rotational torque between the outer ring and the cage by elastic deformation in the radial direction. For this reason, a function as a torque limiter can be added to the constant velocity joint, and a constant velocity joint that is less likely to be damaged can be obtained.

  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 toner image on the photosensitive drum from expanding and contracting to the image transferred onto the transfer material. Can be formed.

  In addition, grease lubrication is required when the outer ring and cage of the constant velocity joint are made of metal. However, at least the outer ring and cage of the above-described outer ring and cage are made of synthetic resin, so that grease lubrication is unnecessary. Can do. As a result, it is possible to assemble and disassemble the constant velocity joint by inserting / removing the cage with respect to the annular space of the outer ring without requiring measures for preventing grease leakage by attaching the boot, thereby facilitating maintenance of the image forming apparatus. In addition, it is possible to eliminate the disadvantage that the transfer material is soiled due to leakage of grease. Further, it is possible to obtain an image forming apparatus with a small operating sound during torque transmission.

  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 charging device 3 uniformly stagnates the entire outer periphery of the photosensitive drum 1 when the photosensitive drum 1 rotates, and then the exposure unit 4 exposes image light based on the image information to static electricity. An electrostatic latent image is formed, toner is supplied onto the electrostatic latent image from the developing unit 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. 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, and 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 and 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.

  3 and 4, the track grooves 16 and 17 are formed on the outer wall surface and the inner wall surface of the annular space 15, respectively, but 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 cage 21 is retained by a retaining ring 18 attached to the inner periphery of the open end of the cup portion 12.

  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 and breaks rapidly when torque exceeds the allowable amount. Therefore, it is preferable to use a crystalline resin.

  Preferred synthetic resins include synthetic resins with high lubricating properties, 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, it is possible to obtain a constant velocity joint with excellent cost performance.

  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 resin can be used as balls 31, but stainless steel, ceramics, and synthetic resin are preferable because there is no need for rusting even without lubrication. A synthetic resin is preferable because it is lighter.

  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 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 the embodiment, the drum shaft 1a of the photosensitive drum 1 and the rotating shaft 2a of the driving motor 2 are connected by a constant velocity joint J to connect the drum shaft 1a of the photosensitive drum 1 and the rotating shaft 2a of the driving motor 2. The photosensitive drum 1 can be rotated at a constant speed without causing uneven speed even if there is a misalignment or inclination. 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 unit 4 and the transfer charger 6 at a position of 180 °, so that the degree of freedom in design can be increased.

  As shown in the embodiment, when the outer ring 11 and the cage 21 of the constant velocity joint J are formed of synthetic resin, grease lubrication can be eliminated.

  For this reason, the maintenance of the image forming apparatus can be facilitated and there is no scattering of grease, so that there is no inconvenience that the transfer material A is soiled. Further, by using the outer ring 11 and the cage 21 as a molded product of a synthetic resin, it is possible to obtain a constant velocity joint J with a small operating sound during torque transmission.

  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 that has no circumferential backlash and is excellent in constant velocity. By driving the drive motor 2, the photosensitive drum 1 can be rotated more effectively at a constant velocity.

  5 and 6 show another example of the constant velocity joint J. FIG. In the constant velocity joint shown in this example, a split groove 41 composed of three slits extending in the axial direction from the opening end of the cup portion 12 is formed between the adjacent track grooves 16 of the cup portion 12 to form the track groove 16. 3 and 4 in that three elastic pieces 42 are provided on the inner periphery, and a protrusion 43 is formed on the inner periphery of each elastic piece 42 on the opening side of the cup portion to prevent the cage 21 from coming off. It is different from the constant velocity joint J shown.

  Since the other structure is the same as the constant velocity joint J shown in FIG. 3 and FIG. 4, the same code | symbol is attached | subjected to the same site | part and description is abbreviate | omitted.

  In the constant velocity joint J shown in FIGS. 5 and 6, the elastic pieces 42 are connected to the protrusions 43 by the contact of the balls 31 when the cage 21 is inserted into the annular space 15 from the opening end side of the cup portion 12. The cage 12 and the ball 31 can be easily assembled in the annular space 15 by being elastically deformed outward in the radial direction of the portion 12, and the assembled product can be prevented from coming off by the protrusion 43.

  Therefore, it is not necessary to use a special tool for assembling the constant velocity joint J, the constant velocity joint J can be easily assembled, and the number of parts can be reduced by the amount that the retaining ring 18 shown in FIG. Can do.

  In the constant velocity joint shown in FIGS. 5 and 6, the elastic force of the elastic piece 42 can be obtained by forming the outer ring 11 with a resin material having a high elastic modulus and forming the cup 12 of the outer ring 11 thick. Thus, it is possible to apply a preload to the ball 31 and to obtain a constant velocity joint with a small amount of play in the rotational direction and excellent in constant velocity.

  Further, when a rotational torque greater than the rotational torque allowed by the elastic modulus of the outer ring 11 is applied, the elastic pieces 42 are elastically deformed outward in the radial direction of the cup portion 12, and between the outer ring 11 and the cage 21. Torque transmission can be cut off. For this reason, a function as a torque limiter can be added to the constant velocity joint J, and an effect can be obtained in preventing the constant velocity joint J from being damaged.

  A retaining ring may be attached to the outer periphery of the open end of the cup portion 12 in order to apply a preload to the ball 31.

  In the constant velocity joint shown in FIG. 5 and FIG. 6, a retaining ring is provided on the outer periphery of the opening end portion of the outer ring 11 under conditions where the rotational torque is larger than the elastic modulus of the outer ring 11 and does not require the function of the torque limiter. Is attached to prevent the elastic piece 42 from being elastically deformed radially outward of the cup portion 12.

  5 and 6, the split groove 41 formed in the cup portion 12 is made of a slit, but the split groove 41 is not limited to this. For example, as shown in FIG. 7, the cup portion 12 may be composed of a wide wide groove in the circumferential direction.

  In FIG. 1, a single color image forming apparatus is described as an example. However, when forming a full color image forming apparatus, four sets of the image forming apparatuses shown in FIG. 1 are prepared, and the four sets of image forming apparatuses are used as transfer materials. 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. Vertical side view of FIG. Partially cutaway front view showing another example of constant velocity joint Vertical side view 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)
J Constant velocity joint 11 Outer ring 15 Annular space 16 Track groove 17 Track groove 21 Cage 22 Second shaft 31 Ball 42 Elastic piece

Claims (4)

A photosensitive drum (1); drive means (2) for rotationally driving the photosensitive drum (1); exposure means (4) for forming an electrostatic latent image on the photosensitive drum (1); 1) The toner image is transferred onto a developing material (5) for supplying toner to the electrostatic latent image on the upper surface and a transfer material conveyed at the same speed as the peripheral speed of the photosensitive drum (1). An image forming apparatus comprising: a transfer shaft (6) configured to connect a drum shaft (1a) of the photosensitive drum (1) and a drive shaft (2a) of the drive device (2) with a shaft coupling;
The shaft coupling has a cup portion (12) whose one end is open, and a guide shaft that forms an annular space (15) with the cup portion (12) on a central axis in the cup portion (12). (14) is provided, at least of the inner peripheral surface of the cup portion (12) forming the outer wall surface of the annular space (15) and the outer peripheral surface of the guide shaft (14) forming the inner wall surface of the annular space (15). on the other hand an outer ring (11) which three track grooves extending in the axial direction (16, 17) are provided at intervals of 120 ° in the circumferential direction, said annular space (15) of the outer ring (11) The cage (21) provided with the second shaft (22) at the end located on the open end side of the outer ring (11) and the outer ring (11) formed by being held by the cage (21) Three balls (31) rollable along the track grooves (16, 17); Yes, and
The outer ring (11) and the cage (21) are molded products of a lubricious synthetic resin that can be injection-molded. The outer ring (11) and the guide shaft (14) are integrally molded, and the cage (21) The second shaft (22) is formed of a constant velocity joint (J) that is integrally molded and does not use grease and a boot that prevents leakage of the grease ,
The outer ring (11) and one to the photosensitive drum shaft of the drum (1) of the second shaft (22) (1a), Rukoto drive shaft of the drive means in the other (2) (2a) is not connected, respectively An image forming apparatus.   The image forming apparatus according to claim 1, wherein the synthetic resin is made of a crystalline resin that can be injection-molded. The image forming apparatus according to claim 1 or 2 was applied a preload to the elastic the ball by using (31) of said outer ring (11). The cup portion (12 ) of the outer ring (11) is divided between adjacent track grooves (16) to form three elastic pieces (42) having the track grooves (16) on the inner periphery, and the elastic pieces ( The image according to any one of claims 1 to 3 , wherein torque transmission between the outer ring (11) and the cage (21) is interrupted by elastic deformation of the outer ring (11) in the radial direction of the outer ring (11). Forming equipment.

Images