JP4711669B2 - 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 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 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.

  In the image forming apparatus using the inconstant-velocity universal joint, the universal joint can be used when the drum shaft and the rotation shaft of the motor are relatively inclined. If there is an approximately parallel arrangement, an intermediate shaft is provided between the opposing portions of the drum shaft and the motor rotation shaft, between the intermediate shaft and the drum shaft, and between the intermediate shaft and the motor rotation shaft. There is a need to incorporate a universal joint between the drum shaft and the rotating shaft of the motor, and two universal joints are required, resulting in an increase in cost.

  The object of the present invention is to always transmit the rotation of the rotating shaft of the motor to the photosensitive drum at a constant speed even when there is a shift in the axis between the drum shaft of the photosensitive drum and the rotating shaft of the motor arranged in parallel. It is an object of the present invention to provide an image forming apparatus capable of forming a high-quality image.

  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 driving means are connected by a shaft joint, the shaft joint has an annular space with one end opened, and the opposite ends are arranged so that the open ends of the annular space face each other. Two outer rings and a joint member having both ends of a cage portion inserted into the annular space of each outer ring, and extending in the axial direction to at least one of the outer wall surface and the inner wall surface in the annular space of each outer ring 3 track grooves Circumferentially formed at intervals of 120 °, is of a rollable ball adopts the configuration comprising a constant velocity joint, held by the cage portion of the joint member along each track groove.

  Here, by using the outer ring of the constant velocity joint as a synthetic resin molded product, the constant velocity joint can be made non-lubricated and the constant velocity joint can be reduced in weight.

  Further, the constant velocity joint can be further reduced in weight by using a synthetic resin as the joint member of the constant velocity joint.

  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, since the drum shaft of the photosensitive drum and the drive shaft of the driving means are connected by the constant velocity joint having two outer rings, the drive shaft of the driving means and the drum shaft of the photosensitive drum are misaligned. Even when there is a tilt or when there is a deviation between the two axes, 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. Images can be formed.

  Further, when the outer ring and the cage of the constant velocity joint are made of metal, grease lubrication is required, and maintenance of the image forming apparatus is difficult, and there is a concern that the transfer material may be soiled due to leakage of the grease. By using a synthetic resin molded product, grease lubrication can be dispensed with. As a result, the maintenance of the image forming apparatus can be facilitated, and the inconvenience that the transfer material is contaminated can be eliminated.

  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 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.

  The rotating shaft 2a as the driving shaft of the driving motor 2 and the drum shaft 1a of the photosensitive drum 1 are connected via a constant velocity joint CVJ.

As shown in FIGS. 3 and 4, the constant velocity joint CVJ includes two outer rings OR ₁ and OR ₂ , a joint member J provided between the outer rings OR ₁ and OR ₂ , the joint member J, and the outer ring. It consists of a ball B that transmits rotational torque between OR ₁ and OR ₂ .

The outer rings OR ₁ and OR _{2 each} have a cup portion 11 that is open at one end, and a connecting shaft 12 is integrally provided at the closed end of the cup portion 11. Further, a guide shaft 13 is provided on the central axis in the cup portion 11, an annular space 14 is formed between the guide shaft 13 and the cup portion 11, and the cup portion 11 that forms the outer wall surface of the annular space 14 is formed. Three track grooves 15, 16 extending in the axial direction are provided on the outer peripheral surface of the guide shaft 13 that forms the inner peripheral surface and the inner wall surface of the annular space 14 at intervals of 120 ° in the circumferential direction.

  In the embodiment, the track grooves 15 and 16 are formed on the outer wall surface and the inner wall surface of the annular space 14, respectively, but the track groove may be provided on one of the outer wall surface and the inner wall surface.

The two outer rings OR ₁ and OR ₂ are disposed to face each other so that the open ends of the cup portion 11 face each other, and the joint member J is incorporated between the cup portions 11.

The joint member J has cage portions 21 inserted into the annular spaces 14 of the outer rings OR ₁ and OR ₂ at both ends, and the cage portions 21 are retaining rings 17 attached to the openings of the outer rings OR ₁ and OR _2. It has been retained by. A pocket 22 is formed in the cage portion 21 corresponding to each of the track grooves 15 and 16 of the outer rings OR ₁ and OR ₂ , and the ball B is incorporated in each pocket 22. Each of the balls B can roll along the track grooves 15 and 16.

As described above, the cage B of the joint member J in which the ball B which can roll along the track grooves 15 and 16 of the _two outer rings OR ₁ and OR ₂ arranged opposite to each other is incorporated between the outer rings OR ₁ and OR _2. When the two outer rings OR ₁ and OR ₂ are misaligned with each other by being held by the portion 21, the joint member J is inclined to absorb the misalignment of the axes, and the two outer rings OR _1. Thus, a constant velocity joint CVJ that can transmit torque at a constant speed between OR ₂ can be obtained.

  Therefore, by connecting the connecting shaft 12 of one outer ring to the rotating shaft 2a of the drive motor 2 and connecting the connecting shaft 2 of the other outer ring to the drum shaft 1a of the photosensitive drum 1, the rotating shaft 2a and the drum shaft 1a are mutually connected. Even when there is a shift in the axis, the rotation of the drive motor 2 can be transmitted to the photosensitive drum 1 at a constant speed.

The outer rings OR ₁ and OR ₂ and the joint member J are made of a synthetic resin molded product , and both gauge portions 21 and 21 of the joint member J are integrated . 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.

Furthermore, by using the outer rings OR ₁ and OR ₂ and the joint member J as molded parts of synthetic resin, it is possible to obtain a constant velocity joint that is light in weight and has a low operating noise during torque transmission, and does not require grease lubrication. It can be.

  Ball B can be made of bearing steel, stainless steel, ceramics, synthetic resin, or the like, but stainless steel, ceramics, or synthetic resin is preferable because there is no need to worry about rust even without lubrication. A synthetic resin is preferable because it is lighter.

In the outer rings OR ₁ and OR ₂ , the cup portion 11 and the guide shaft 13 are integrally formed of synthetic resin. However, the guide shaft 13 is formed of ceramics, steel, stainless steel, aluminum alloy or the like, and the cup portion 11 is formed. You may make it couple | bond with.

  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 CVJ 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 is expanded or contracted by the exposure unit 4, or the image is expanded or contracted when the toner image on the photosensitive drum 1 is transferred to the transfer material A by the transfer charger 6. Can be prevented from occurring.

  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.

Further, since the outer rings OR ₁ and OR _{2 of} the constant velocity joint CVJ and the joint member J are molded products 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 rings OR ₁ , OR ₂ and the joint member J as a synthetic resin molded product, a constant velocity joint CVJ having a low operating noise during torque transmission can be obtained.

Like the constant velocity joint CVJ shown in FIG. 3 and FIG. 4, the outer rings OR ₁ and OR ₂ are formed of a synthetic resin, so that the ball B is preloaded using the elasticity of the outer rings OR ₁ and OR _2. Can be granted.

  Specifically, the ball B is preloaded by making the inner diameter between the track groove 15 formed on the inner circumference of the cup portion 11 and the track groove 16 formed on the outer circumference of the guide shaft 13 smaller than the ball diameter of the ball B. Can be granted. As a result, it is possible to obtain a constant velocity joint CVJ that is free of circumferential backlash and is excellent in constant velocity, and by driving the drive motor 2, the photosensitive drum 1 can be more effectively rotated at a constant velocity.

Further, as shown in FIG. 5, at least one outer ring, for example, three split grooves 18 extending in the axial direction from the opening end are provided between the track groove 15 and the track groove 15 of the cup portion 11 of the outer ring OR _1. By forming and dividing the cup portion 11 into three in the circumferential direction, an elastic piece 19 that can be elastically deformed in the radial direction of the cup portion 11 can be formed between the adjacent split grooves 18. With such a structure, when a rotational torque greater than the rotational torque allowed by the elastic modulus of the outer ring is applied, each elastic piece 19 is elastically deformed radially outward of the cup portion 11 and the outer ring OR _1. Torque transmission between the joint member J and the joint member J can be cut off. Therefore, a function as a torque limiter can be added to the constant velocity joint CVJ, and an effect can be obtained in preventing the drive motor 2, the photosensitive drum 1 and the constant velocity joint CVJ from being damaged.

The elastic piece 19 formed from the above-described split groove 18 can also be formed to apply a preload to the ball B by using the elastic force of the elastic piece 19 in addition to the torque limiter function. In this case, it is desirable to form three split grooves 18 in both of the _two outer rings OR ₁ and OR 2 that are arranged to face each other. The constant velocity joint in which the preload is applied to the ball B by the elastic piece 19 can apply the preload without strictly managing the dimensional accuracy of each component, and therefore an excellent image with no play in the circumferential direction at a low price. A forming device can be obtained.

  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. Sectional view along line IV-IV in FIG. Sectional view showing 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)
CVJ constant velocity joints OR ₁ , OR ₂ outer ring J joint member B ball 14 annular space 15 track groove 18 split groove 19 elastic piece 21 cage part

Claims (3)

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 (11) whose one end is open, and a guide shaft that forms an annular space (14) with the cup portion (11) on the central axis in the cup portion (11). (13) is provided and is inserted into _two outer rings (OR ₁ , OR ₂ ) facing each other so that the opening ends of the annular space (14) face each other , and the annular space (14) of each outer ring. A joint member (J) having a cage portion (21, 21) at both ends, and an inner peripheral surface of the cup portion (11) in the annular space (14) of each outer ring (OR ₁ , OR ₂ ). Three track grooves (15) extending in the axial direction are formed on at least one of the outer wall surface and the inner wall surface that is the outer peripheral surface of the guide shaft (13) at intervals of 120 ° in the circumferential direction, and each track groove (15 16) A ball (B) rollable along each of the joint members (J) It consists of a constant velocity joint (CVJ) that is held by the cage part (21) and does not use grease and boots that prevent leakage of the grease ,
The outer ring (OR ₁ , OR ₂ ) is an integrally molded product of a lubricious synthetic resin in which the cup portion (11) and the guide shaft (13) can be injection- molded, and the joint member (J) The cage portion (21, 21) is an integrally injection-moldable product made of a lubricious synthetic resin, and the drum shaft (1a) of the photosensitive drum (1) is placed on _{one of} the outer rings (OR ₁ , OR ₂ ) and the other The image forming apparatus is characterized in that the drive shaft (2a) of the drive means (2) is connected to each other. The image forming apparatus according to claim 1 , wherein a preload is applied to the ball (B) using elasticity of a synthetic resin of the outer ring (OR ₁ , OR ₂ ). The cup portion (11) of the outer ring (OR ₁ , OR ₂ ) is divided between adjacent track grooves (15) to form three elastic pieces (19) having track grooves (15) on the inner periphery, Torque transmission between the outer ring (OR ₁ , OR ₂ ) and the joint member (J) is cut off by elastic deformation of the outer ring (OR ₁ , OR ₂ ) in the radial direction of the outer ring (19) of the elastic piece (19). The image forming apparatus according to claim 1 or 2 .

Images