JP2004252487A - Image forming apparatus using endless belt - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an intermediate transfer belt from cracking at its end by making the gripping force of a driving roll uniform along the axis. <P>SOLUTION: A rib 41 is provided at a side end part of an intermediate transfer belt 4 and slid while abutting against a rib guide 17 provided at an end of a driving roll 11 to guide an intermediate transfer body 4. Here, the rib guide 17 is made rotatable independently of the driving roll 11. Further, a gap G is formed by making the diameter D1 of the rib guide a little larger or a little smaller than the diameter D2 of the driving roll 11. Consequently, the gripping force decreases at both breadthwise ends of the belt 4 and the abutting force between the rib 41 and rib guide 17 by a walk of the belt 4 can be decreased. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a laser printer, and more particularly, to an image forming apparatus that forms an image using a belt-shaped image forming member, particularly a belt-shaped photoconductor and a belt-shaped intermediate transfer body. About.

  2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine or a printer, a method in which an unfixed toner image formed on a latent image carrier such as a photosensitive drum is transferred to a recording medium such as paper to obtain a printed image is used. Can be As a method of transferring the unfixed toner image to the recording medium, a method of directly transferring the unfixed toner image to the recording medium, and a method of transferring the unfixed toner image formed on the latent image carrier to a drum shape or an endless belt shape A method is known in which a primary transfer is performed on an intermediate transfer member composed of a film member described above, and then an unfixed toner image on the intermediate transfer member is secondarily transferred onto a recording medium again to obtain a copied image.

  FIG. 9 is a schematic diagram illustrating a main configuration of a color printer as an example of an image forming apparatus using a belt-shaped intermediate transfer member. In the figure, the surface of a latent image carrier (hereinafter, referred to as a “photoconductor drum”) 1 such as a photoconductor drum is uniformly charged with a predetermined charge by a charger 2, An electrostatic latent image corresponding to the first color image signal is formed by the writing scan. The electrostatic latent image reaches a position facing the first color developing unit of the developing device unit 3 by the rotation of the photosensitive drum 1 in the direction A, and is subjected to toner development by the first color developing unit. The photoconductor drum 1 carries the toner image T and further rotates.

  In accordance with the toner developing operation, the intermediate transfer belt 4 moves at substantially the same speed as the peripheral speed of the photosensitive drum 1, and the intermediate transfer belt 4 immediately below the position where the photosensitive drum 1 contacts the intermediate transfer belt 4. In the primary transfer portion where the primary transfer roll 5 disposed in contact with the photosensitive drum 4 is disposed, the transfer electric field having a polarity opposite to the charge polarity of the toner applied to the primary transfer roll 5 is applied to the photosensitive drum 1. The carried toner image T is primarily transferred to the intermediate transfer belt 4. Thus, the primary transfer cycle ends.

  The toner image primary-transferred to the intermediate transfer belt 4 reaches the secondary transfer section where the secondary transfer roll 6 is disposed by the orbital movement of the intermediate transfer belt 4. In the case of a full-color image forming apparatus, the process from the formation of a latent image to the primary transfer of a toner image is repeated for a predetermined number of colors (generally, yellow (Y), magenta (M), cyan (C), and black (Bk)). A color toner image is formed on the intermediate transfer belt 4 by superimposing a multicolor toner.

To form a toner image of each color, a developing device unit 3 yellow developing unit 3 _-1, magenta developing device _3-2, cyan developer 3 _-3 and black developing unit 3 _-4 rotating device consisting of four color developing devices The latent image of each color formed on the photosensitive drum 1 can be sequentially developed.

  After the first color toner image carried on the photosensitive drum 1 has been transferred onto the intermediate transfer belt 4 at the primary transfer section, the residual toner on the photosensitive drum 1 is removed by the photosensitive cleaner 7 and shown in FIG. After the charge is neutralized by the neutralizer, the next latent image corresponding to the second color is formed. The electrostatic latent image of the second color is also developed in the same manner as the first color, and the toner image of the second color is transferred on the intermediate transfer belt 4 so as to overlap the previously transferred toner image of the first color. You. Hereinafter, the third and subsequent colors are similarly multiply transferred to the intermediate transfer belt 4, and as a result, a color toner image is formed on the intermediate transfer belt 4 in which unfixed plural color toners are superimposed.

  When the intermediate transfer belt 4 on which the toner images of all colors have been primary-transferred reaches the secondary transfer position, the recording paper P as a recording medium sent out from the paper feed tray 8 is timely transferred to the secondary transfer position. Is sent to

  When the recording paper P is nipped and conveyed by the secondary transfer roll 6 and the intermediate transfer belt 4, a transfer electric field formed by a transfer voltage having a polarity opposite to the charging polarity of the toner image applied to the secondary transfer roll 6 is applied. The toner image on the intermediate transfer belt 4 is secondarily transferred onto the recording paper P.

  The recording paper P on which the toner image has been secondarily transferred is sent to the fixing device 9, where the toner image is fixed to the recording paper P by a heating / pressing process, and the image forming process ends. In addition, a static eliminator (not shown) for neutralizing the recording paper P on which the toner image has been secondarily transferred is disposed downstream of the secondary transfer roll 6.

  The secondary transfer roll 6 is provided so as to freely contact and separate from the intermediate transfer belt 4 in the direction of arrow C, contacts the recording paper P as it enters, and separates as the recording paper P is discharged. The secondary transfer roll 6 returns to the standby position when the secondary transfer ends. Similarly, the cleaner 10 disposed opposite to the intermediate transfer belt 4 abuts against the intermediate transfer belt 4 like the secondary transfer roll P in order to clean the toner image not transferred to the recording paper P.・ Separate.

  In a color image forming apparatus using such an intermediate transfer belt, since a composite toner image (superimposed image of each color toner image) already multiplex-transferred on the intermediate belt is collectively transferred to a recording medium, a latent image is formed. This method has an advantage that it is possible to effectively prevent the occurrence of positional deviation and image disorder between toner images in a method of sequentially transferring toner images of each color from a carrier directly to a recording medium.

  The intermediate transfer belt 4 is stretched by a drive roll 11, an idle roll 12, a secondary transfer backup roll 13, and a tension roll 14, and is conveyed in the direction of arrow B by the drive roll 11. The intermediate transfer belt 4 is provided with a regulating member including a rib and a rib guide for regulating the position of the intermediate transfer belt 4 in the axial direction, such as the drive roll 11.

  On the other hand, a coating layer of a high friction material is formed on the surface of the drive roll 11 so that the intermediate transfer belt 4 does not slip even when a load is applied by the cleaner 10 or the secondary transfer roll 6.

  When the intermediate transfer belt 4 is conveyed in a circulating manner, a conventional method is used in order to prevent the speed of the intermediate transfer belt 4 from changing in the circulating direction, restrict the position of the driving roll 11 in the axial direction, and prevent the end of the intermediate transfer belt 4 from breaking. Various configurations have been proposed.

  JP-A-2-27383 discloses that a rib is provided at one end outside an image area of an intermediate transfer belt, a groove corresponding to the rib is provided on a plurality of rolls including a driving roll, and a friction coefficient of the rib is provided. Is different from the friction coefficient of the intermediate transfer belt. Japanese Patent Application Laid-Open No. Hei 4-257888 discloses that ribs are provided at both ends of a belt wound around a driving roll and a driven roll, and grooves corresponding to the ribs are provided at both ends of both the driving roll and the driven roll. ing.

  Japanese Patent Application Laid-Open No. 5-134556 discloses a transfer belt in which a tape as a reinforcing member is attached to an end. In this transfer belt, in order to prevent the transfer belt from floating at the contact portion between the roll and the tape, and to prevent cracks from occurring at the boundary between the transfer belt and the reinforcing member, at a portion corresponding to the tape position, The outer diameter of the roll is reduced.

  Japanese Patent Application Laid-Open Nos. 9-175686 and 9-16512 disclose a technique for sewing a middle transfer belt and a rib to prevent the rib from dropping off from the intermediate transfer belt.

On the other hand, as a technique for preventing slippage between the intermediate transfer belt and the drive roll, JP-A-6-35331 discloses a technique for providing irregularities of 20 to 100 microns on the drive roll surface, and JP-A-8-152812 discloses an intermediate transfer belt. There is disclosed a technique of applying an adhesive or a high-friction resin to a part or the whole of one or both of an inner surface and a drive roll.
JP-A-2-27383 JP-A-4-257888 JP-A-5-134556 JP-A-9-175686 JP-A-9-16512

  In an image forming apparatus having an intermediate transfer belt and a driving roll for driving the intermediate transfer belt, and a rib and a rib guide for preventing the meandering of the intermediate transfer belt, the intermediate transfer belt is based on a polycarbonate-based resin and a polyimide-based resin. A semiconductive film 50 to 100 microns thick containing a resistance adjusting material. The surface of the drive roll is generally treated with high friction to prevent slippage with the belt.

  As the high friction treatment, a high friction resin such as urethane rubber is coated on the surface of the aluminum roll so that the friction coefficient between the drive roll and the intermediate transfer belt can be maintained for a long time. However, when the drive roll or belt is new, the friction coefficient of the surface of the drive roll is too high, so that the belt repeatedly repeats stick-slip in the axial direction on the drive roll, and a squeaking noise may be generated.

  Further, the intermediate transfer belt stretched by the plurality of rolls moves (walks) in the axial direction as described above while being transported. A certain amount or more of the walk is regulated by the ribs and the rib guides described above. However, if the state in which the rib and the rib guide are pressed against each other by the walk is continued for a long period of time, especially when the mechanical strength of the end portion of the intermediate transfer belt is insufficient, the intermediate transfer belt cannot withstand this state and breaks. However, there is a problem that the image forming operation may not be continued.

  Generally, a strong force that causes the belt to break is caused by a decrease in the flatness of the belt device due to poor levelness of the device main body, a twist due to component stacking and assembly errors of the front and rear side plates of the device main body, and both ends of the belt itself in the axial direction. It occurs due to the difference in circumference at However, the intermediate transfer belt or the like as an image carrier in the image forming apparatus may further be broken due to factors specific to the intermediate transfer belt or the like.

  The mechanism of the problem that the intermediate transfer belt is broken will be described. The combination of a new drive roll and a new intermediate transfer belt has a high coefficient of friction and a large grip between the drive roll and the intermediate transfer belt. Therefore, even when the alignment (parallelism of the shaft) of each roll on which the intermediate transfer belt is stretched slightly deviates from a predetermined value, the belt is likely to walk. Therefore, the belt moves to one side within a short period of several tens of cycles from the beginning, and the rib and the rib guide abut against each other with a strong gripping force.

  The following forces act on the side surfaces of the ribs at the position where the belt is applied to the drive roll and when the belt passes through the drive roll. FIG. 10 is a cross-sectional view of the intermediate transfer belt 4 applied to the drive roll 11, and FIG. 11 is a cross-sectional view of a contact portion between the drive roll 11 and the intermediate transfer belt 4. In both figures, ribs 41 are provided at both ends of the rear surface of the intermediate transfer belt 4 to abut against the side end surface of the drive roll 11 to prevent the intermediate transfer belt 4 from walking.

  When the intermediate transfer belt 4 walks and comes into contact with the side surface of the drive roll 11, a force F1 acts on the side surface of the rib 41 in a portion R1 where the intermediate transfer belt 4 starts to be applied to the drive roll 11. That is, a force acts such that the intermediate transfer belt 4 floats up and rides on the drive roll 11. The intermediate transfer belt 4 that has once floated no longer floats at the position R2 where it comes off the drive roll 11.

  FIG. 12 is a cross-sectional view of the intermediate transfer belt 4 when the floating occurs. The intermediate transfer belt 4 is lifted by the force F1, and at the same time, a strong pressing force acts on the side surface of the rib 41, so that a bulge portion RU is generated. This raised portion RU is eliminated in the portion R2. That is, in the side end portion of the intermediate transfer belt 4, deformation in one direction and deformation in the opposite direction occur alternately near the drive roll 11, and stress concentration and stress release are repeated.

  The force of pressing the rib 41 against the side surface of the drive roll 11 increases as the gripping force increases and the alignment decreases, and the intermediate transfer belt 4 is easily lifted. When the rib 41 is strongly pressed against the side surface of the driving roll 11, not only the stress concentration and the stress release are repeated, but also the driving force of the belt is transmitted from the side surface of the roll via the rib of the belt, and the belt surface is transferred from the roll surface to the belt. Does not necessarily coincide with the original driving speed, which results in distortion, resulting in accumulation of stress and squeaking of the intermediate transfer belt 4 and the driving roll 11.

  Stress concentration and stress release are repeated at the bulging portion RU, and furthermore, accumulation of distortion at the belt end causes a local crack CR due to fatigue if the operation is continued as it is. This local crack CR eventually breaks the entire intermediate transfer belt 4 (see FIG. 13). In addition, there is a risk that the entire intermediate transfer belt 4 is easily broken from the notch N existing at the end of the intermediate transfer belt 4 (see FIG. 14).

  In order to prevent the intermediate transfer belt from walking, the degree of parallelism between the rolls on which the intermediate transfer belt is stretched is kept very small, and the difference in the circumference of the intermediate transfer belt is processed with high precision so that the front and rear sides are Of course, efforts to maintain strict component accuracy and assembly accuracy, such as reducing the dimensional difference on the side, are necessary.

  However, increasing the accuracy of the intermediate transfer belt and rolls complicates the processing, assembling, and adjusting steps, and it is not easy to achieve the target in consideration of mass productivity. Even if the manufacturing problem is solved, if the level of the installation surface of the image forming apparatus itself is not ensured, the parallelism between the rolls on which the intermediate transfer belt is stretched may be reduced. Had a problem that it became impossible to secure it.

  Of course, the precision of parts and assembly must be strictly controlled, but in addition to that, other factors that may cause a walk that produces the above-mentioned strong pressing force, that is, improvements in grip force, etc. are necessary. Achievement is required.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that solves the above-mentioned problems and prevents an endless belt, which is an image carrier, from being deformed and broken by a force in which a rib and a roll come into contact with each other during a walk. And

  In order to achieve the above object, the present invention comprises an endless belt as a toner image carrier that holds and conveys a toner image, and a plurality of rolls including a driving roll for stretching and conveying the endless belt. Belt tension means, a rib member provided along both ends of the inner peripheral surface of the endless belt, and having an inner side surface at the axial center side of the drive roll and an outer side surface at the axial end side; In an image forming apparatus using an endless belt provided at both ends of a drive roll and having a rib guide member that contacts the inside of each of the rib members and guides the rib member, the vicinity of both ends of the drive roll and the A first feature resides in that a gap is provided between the endless belt and the rib guide member can be independently rotated with respect to the drive roll.

  Further, the present invention has a second feature in that the diameter of the rib guide member is larger than the diameter of the driving roll. Further, the present invention has a third feature in that the diameter of the end portion of the driving roll is smaller than that of the center portion.

  According to the first to third features, since the rib guide member can be independently rotated with respect to the roll, a force for driving the belt from the side surface of the roll via the rib of the belt is cut off. Since the belt is driven only from the roll surface, the belt is not distorted. For this reason, stress and squeak noise are not generated on the belt. In addition, a gap is formed between the end of the drive roll and the endless belt, and the grip at the end of the drive roll is reduced.

  As is apparent from the above description, according to the present invention, the grip force that tends to increase at the end of the endless belt can be made uniform in the axial direction of the drive roll. The lifting phenomenon can be eliminated. Further, a gap is generated between the end portion of the driving roll and the endless belt, and the grip force at the end of the driving roll is reduced. As a result, it is possible to greatly reduce the occurrence of breakage such as cracks in the belt due to fatigue caused by repeated deformation of the belt due to the lifting.

  Hereinafter, a color image forming apparatus to which the present invention is applied will be described in detail with reference to the accompanying drawings. Here, the configuration, operation, and the like described with reference to FIG. 9 are used, and the description will be given with reference to FIG.

  FIG. 4 is a diagram illustrating a state of tension applied to the intermediate transfer belt stretched between the rolls. When tension is applied to the tension roll 14 by stretching the intermediate transfer belt 4 around the drive roll 11, the idle roll 12, the tension roll 14, and the secondary transfer backup roll 13, a tension line 15 shown in FIG. 4 appears. The tension line 15 is a “wrinkle” on the intermediate transfer belt 4 caused by uneven tension applied to the intermediate transfer belt 4. From this “wrinkle”, it is understood that a larger tension is applied near the side end of the intermediate transfer belt 4 than at the center. Due to the difference in the tension, the grip force Gr on the drive roll 11 is distributed as shown in FIG. The grip force Gr is extremely large at both ends of the drive roll 11.

  FIG. 5 is a diagram illustrating the grip force Gr of the drive roll 11 having different use periods. Here, the distribution of the grip force Gr is measured for four types of drive rolls 11 having different use periods of the intermediate transfer belt 4, that is, different numbers of times of use (kcs). As can be seen from this figure, the unevenness of the gripping force Gr becomes more remarkable as the drive roll 11 is closer to a new one. As the period of use increases, the difference in the gripping force Gr of the drive roll 11 in the axial direction decreases.

  The reason why the grip force at both ends of the drive roll is reduced is that the degree of dirt on the roll surface advances. FIG. 6 is a diagram showing the degree of contamination of the drive roll 11 for each use period. As shown in the figure, dirt has spread from both ends of the drive roll 11. This stain is mainly obtained by rubbing the back surface of the intermediate transfer belt 4, and the other major stain is toner floating in the apparatus. The dirt saturates over the entire length of the drive roll 11 after approximately 10 km orbit (kcs).

  As described above, since the grip force is large when the drive roll 11 is new, the walk of the intermediate belt 4 easily causes damage (FIGS. 13 and 14) due to repeated deformation of the side end portion of the intermediate transfer belt 4. If the tension roller 14 is loosened to reduce the belt tension, the grip force is reduced and the intermediate transfer belt 4 can be prevented from being damaged. However, if the grip force is too small, the toner color of each color superimposed on the intermediate transfer belt 4 can be reduced. There is a problem that displacement occurs.

  FIG. 7 is a diagram showing the relationship between the total grip force and the color misregistration in the entire axial direction of the drive roll 11 using the belt tension as a parameter. Here, the total grip force refers to a stationary starting torque measured by fixing the idle roll 12 and the intermediate transfer belt 4 and mounting a torque meter on the shaft of the drive roll 4 in this state. In the case where the belt tension is 4 kgf, if the allowable value of the burden on the intermediate transfer belt 4 in the allowable value of the color shift of the entire image forming apparatus is, for example, 25 μm, the total grip force is 6 kgf or more from FIG. It turns out that it must be.

  On the other hand, as described above, since the dirt on the drive roll 11 is saturated when the number of belt rotations is about 10 kcs, the total grip force is set to be equal to or more than 6 kgf at least during a use period when the number of belt rotations is about 10 kcs or more. There must be. If it is attempted to secure a large gripping force when the number of belt rotations is about 10 kcs or more, the total gripping force becomes extremely large in the initial use state in which the dirt has not progressed, and the deformation of the intermediate transfer belt 4 due to the walk cannot be avoided. The breakage of the intermediate belt 4 occurs when the grip force is large at the beginning of use.

  Therefore, in the present embodiment, the following measures are taken in order to achieve both the reduction of the color misregistration and the prevention of the damage of the intermediate transfer belt 4. That is, as described above, the grip force Gr is large at the end of the drive roll 11 in the axial direction, and this phenomenon is particularly remarkable in the early stage of use.

  FIG. 8 is a cross-sectional view of a main part showing a configuration of the driving roll 11 and the intermediate transfer belt 4. In the figure, a drive roll 11 includes a roll body 11a and a high friction material portion 11b coated on the surface of the roll body 11a. The high friction material portion 11b is provided to prevent the intermediate transfer belt 4 from slipping even when a load is applied by the cleaner 10 or the secondary transfer roll 6. For example, an aluminum tube is used for the roll body 11a, and a polyurethane coating layer (5 to 50 μm: preferably 25 μm) is used for the high friction material portion 11b.

  A rib guide 17 is provided at the shaft end of the driving roll 11. The rib guide 17 is preferably made of a resin material having a smooth surface and good slidability, for example, polyacetal. Further, it is preferable that the rib guide 17 is not fixed to the side surface of the roll body 11b but is separated therefrom. Note that the rib guide is similarly provided on the idle roll 12 and the tension roll 14.

The intermediate transfer belt 4 is made of a polyimide resin and has a thickness of 50 to 100 μm, a volume resistivity of 10 ⁹ to 10 ¹² Ω · cm, and a surface conductivity adjusted to 10 ¹¹ to 10 ¹³ Ω / □. Film. The intermediate transfer belt 4 may be made of an acrylic resin, a vinyl chloride resin, a polycarbonate resin, or the like, as long as it is a semiconductive resin material whose thickness, volume resistivity, and surface resistivity fall within the above ranges. Containing a resistance stabilizing material.

  Ribs 41, 41 are provided inside the intermediate transfer belt 4, that is, at both ends on the back side of the image carrying surface. The inner surfaces of the ribs 41, that is, the surfaces of the drive roll 11 near the center in the axial direction come into contact with the ends of the rib guides 17 provided at both ends of the drive roll 11 from outside, and the drive roll of the intermediate transfer belt 4 11 functions to regulate the movement in the axial direction. Tapes 18, 18 as reinforcing members for increasing the strength of the end portion of the intermediate transfer belt 4 are joined to the outside of the intermediate transfer belt 4, that is, both ends of the image carrying surface. As an example of the tape material, polyethylene terephthalate (PET) having a thickness of 50 to 100 μm can be used.

  Here, an embodiment of the present invention will be described with reference to FIG. FIG. 1 is an enlarged view of a drive roll shaft end. In this embodiment, the rib guide 17 is configured to be rotatable independently of the drive roll 11 as one of the methods for reducing friction near the shaft end of the drive roll 11.

  Now, assuming that the rib guide 17 rotates together with the drive roll 11, the rib 41 of the belt is in contact with the side surface of the rib guide 17, so that the rib 41 obtains the driving force from the side surface of the rib guide 17. . At this time, since the rotation speed of the side surface of the rib guide 17 at the position where the rib 41 is in contact is smaller than the rotation speed of the peripheral surface of the drive roll 11, a speed difference is generated between the center portion and both end portions of the belt 4, and 4 will be distorted.

  However, in this embodiment, since the rib guide 17 is rotatable with respect to the drive roll 11, the driving force for driving the belt 4 from the side surface of the roll via the belt rib 41 is cut off. As a result, the belt 4 is driven only from the peripheral surface of the drive roll, and it is possible to prevent the accumulation of distortion due to the speed difference at the end of the belt 4. For this reason, no distortion occurs in the belt 4 and no stress is applied to the belt. In addition, squeak noise is not generated from the belt, and damage to the end of the belt 4 can be prevented or reduced.

  Also, as in FIG. 1, when the rib guide is provided on both sides of the tension roll 14 and the rib guide is made rotatable, the same effect as that of the drive roll can be obtained. The idle roll 12 and the secondary transfer backup roll 13 may be provided with the same rib guide as described above.

  As described above, when the above-described rib guide is provided on the drive roll 11 and at least one of the tension roll 14 and the idle roll 12, in the belt unit that stretches and transports the endless belt 4, these rib guides are On the same end side of each of the rolls 11, 14, and 12, it is preferable that the rolls are positioned within the range of 0 to 0.5 mm per 350 mm width at the axial position.

  Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, the diameter of the rib guide 17 is made larger than the outer diameter of the drive roll 11, and the rib guide 17 is configured to be rotatable independently of the drive roll 11. As shown in the figure, the diameter D1 of the rib guide 17 is slightly larger than the diameter D2 of the drive roll 11, and the rib guide 17 is configured to be rotatable with respect to the drive roll 11.

  By providing a difference between the diameters of the two, a gap G is generated between the shaft end of the drive roll 11 and the back surface of the intermediate transfer belt 4 as shown in the drawing. In other words, the frictional force between the drive roll 11 and the belt 4 is reduced to zero or reduced in the vicinity of the area b where the gap G is generated. As a result, the grip force at the shaft end of the drive roll 11 can be reduced. Further, since the rib guide 17 is rotatable with respect to the driving roll 11, when the belt 4 is rotated by being driven by the driving roll 11, a force for driving the belt 4 from the side surface of the roll via the rib 41 of the belt is provided. Almost completely gone. Therefore, the belt 4 is driven only from the peripheral surface of the driving roll, and the belt 4 is not distorted. As a result, breakage at the end of the belt 4 can be prevented or reduced.

  Also, as in FIG. 1, the tension roll 14 is provided on both sides thereof with a rib guide having a diameter slightly larger than the diameter of the tension roll 14 so that the rib guide is rotatable. Similar effects can be obtained. The idle roll 12 and the secondary transfer backup roll 13 may be provided with the same rib guide as described above.

  In the same manner as in the first embodiment, when the above-described rib guide is provided on the driving roll 11 and at least one of the tension roll 14 and the idle roll 12, the belt unit that stretches and transports the endless belt 4 is provided. It is preferable that these rib guides be located within the range of 0 to 0.5 mm per 350 mm in width in the axial direction on the same end side of each of the rolls 11, 14, and 12. Further, it was experimentally confirmed that the diameter D1 of the rib guide 17 should be larger than the diameter D2 of each of the rolls 11, 14, and 12 by about 0.3 mm to 0.6 mm.

  Next, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, as shown, instead of increasing the diameter of the rib guide 17, the diameter of the rib guide 17 and the end of the driving roll 11 is reduced, and the rib guide 17 is independent of the driving roll 11. It is configured to be rotatable. FIG. 3 shows that the diameter D3 of a portion facing the back surface of the intermediate transfer belt 4 at the end of the driving roll 11, that is, inside the rib 41, is slightly smaller than the diameter D2 of the other portion, and the intermediate transfer is performed at that portion b. A gap is formed between the belt 4 and the back surface.

  Next, a fourth embodiment of the present invention will be described. In this embodiment, the sliding resistance of the rib guide 17 with the rib 41 is reduced by selecting the material of the rib guide 17 and finishing the surface thereof, in other words, the coefficient of friction of the sliding surface of the rib guide 17 with the rib 41 is reduced. 41, the force F1 (see FIG. 11) in the direction in which the intermediate transfer belt 4 runs on the drive roll 11 is reduced, and as a result, the height of the raised portion RU is reduced. Things. As the rib guide 17, it is preferable to use a resin material having a smooth surface and good slidability, for example, polyacetal. When this embodiment is applied to the first and second embodiments, a better effect can be obtained.

FIG. 2 is a cross-sectional view of a main part showing a mode of contact between a driving roll and an intermediate transfer belt according to the first embodiment of the present invention. FIG. 9 is a cross-sectional view of a main part showing a mode of contact between a driving roll and an intermediate transfer belt according to a second embodiment of the present invention. FIG. 13 is a cross-sectional view of a main part illustrating a state of contact between a driving roll and an intermediate transfer belt according to a third embodiment of the present invention. FIG. 3 is a diagram illustrating a tension and a grip force applied to an intermediate transfer belt. FIG. 4 is a diagram illustrating grip force of an intermediate transfer belt and a driving roll in relation to the number of times of use. It is a figure which shows the drive roll to which dirt adhered. FIG. 4 is a diagram illustrating a relationship between a total grip force and a color shift amount. FIG. 3 is a cross-sectional view of a main part illustrating a state of contact between a driving roll and an intermediate transfer belt. FIG. 2 is a schematic diagram illustrating a configuration of an image forming apparatus. FIG. 4 is a cross-sectional view of a main part showing the intermediate transfer belt in a state where the intermediate transfer belt is in contact with a driving roll. FIG. 5 is a perspective view illustrating an example of a crack at an end of the intermediate transfer belt. FIG. 5 is a diagram illustrating a state in which an end portion of the intermediate transfer belt is swelled. FIG. 5 is a perspective view illustrating an example of a crack at an end of the intermediate transfer belt. FIG. 5 is a perspective view illustrating an example of a crack at an end of the intermediate transfer belt.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor, 2 ... Charging roll, 3 ... Developing unit, 4 ... Intermediate transfer belt, 17 ... Rib guide, 18 ... Reinforcement tape, 41 ... Rib.

Claims (6)

An endless belt as a toner image carrier that holds and conveys the toner image, a belt stretching unit including a plurality of rolls including a drive roll for stretching and conveying the endless belt, and an inner peripheral surface of the endless belt A rib member provided along both ends and having an inner side surface on the axial center side of the drive roll and an outer side surface on the axial end side, and disposed at both ends of the drive roll; In an image forming apparatus using an endless belt having a rib guide member that guides the rib member by contacting each inside,
An image forming apparatus using an endless belt, wherein a gap is provided between the vicinity of both ends of the drive roll and the endless belt, and the rib guide member can be independently rotated with respect to the drive roll. . An endless belt as a toner image carrier that holds and conveys the toner image, a belt stretching unit including a plurality of rolls including a drive roll for stretching and conveying the endless belt, and an inner peripheral surface of the endless belt A rib member provided along both ends and having an inner side surface on the axial center side of the drive roll and an outer side surface on the axial end side, and disposed at both ends of the drive roll; In an image forming apparatus using an endless belt having a rib guide member that guides the rib member by contacting each inside,
An image forming apparatus using an endless belt, wherein the rib guide member can be independently rotated with respect to the drive roll, and the diameter of the rib guide member is larger than the diameter of the drive roll. An endless belt as a toner image carrier that holds and conveys the toner image, a belt stretching unit including a plurality of rolls including a drive roll for stretching and conveying the endless belt, and an inner peripheral surface of the endless belt A rib member provided along both ends and having an inner side surface on the axial center side of the drive roll and an outer side surface on the axial end side, and disposed at both ends of the drive roll; In an image forming apparatus using an endless belt having a rib guide member that guides the rib member by contacting each inside,
An image forming apparatus using an endless belt, wherein the rib guide member is independently rotatable with respect to the drive roll, and a diameter of the end of the drive roll is smaller than that of a center portion.    4. An image forming apparatus using an endless belt according to claim 1, wherein reinforcing members are provided along both ends of the toner image carrying surface of the endless belt.   The plurality of rolls include an idle roll or a tension roll, and a rib guide member that guides each of the rib members is disposed at both ends of the idle roll or the tension roll, and the rib guide member is provided with respect to the idle roll or the tension roll. An image forming apparatus using an endless belt according to any one of claims 1 to 3, wherein the image forming apparatus can be independently rotated. The image forming apparatus using an endless belt according to any one of claims 1 to 3, wherein the rib guide member is made of a material having a lower coefficient of friction than the rib member.

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