JP4410549B2 - Belt device and image forming apparatus - Google Patents

Description

  The present invention relates to a belt device and an image forming apparatus, and more particularly to a configuration that stabilizes the behavior during movement of a belt and prevents the occurrence of defective images.

In an electrophotographic image forming apparatus, an endless belt body that is circulated and provided with a function of a photoconductor, an intermediate transfer, and a function of conveying transfer paper is used.
In the case of a photosensitive belt, this endless belt body has a feature that it has a high degree of freedom in an occupied space with respect to the arrangement of devices such as an exposure device and a developing device, and thus leads to downsizing of an image forming apparatus. .
On the other hand, as for the time required to obtain a copy output, the demand for full-color and monochrome-like speeds is desired from the market. There has been proposed a so-called tandem type in which an image is formed, those single color toner images are sequentially transferred, and a composite color image is recorded on a sheet (for example, Non-Patent Document 1).
In the case of this method, an intermediate transfer belt or an endless belt of a paper conveying belt is used to sequentially transfer a plurality of images.

  The endless belt is wound around a plurality of rollers. The configuration is generally composed of one drive roller that applies a driving force to the belt, one tension roller that applies tension to stably convey the belt, and a plurality of driven rollers that define the belt conveyance path. Is.

FIG. 1 is a diagram showing an arrangement configuration of a sheet conveying belt used in an electrophotographic apparatus of a tandem type direct transfer system and peripheral devices related to image formation.
In FIG. 1, on one of the stretched surfaces of the paper conveying belt 10, an image forming means 16 is formed in parallel for forming images of each color of yellow, magenta, cyan, and black sandwiched between opposing rollers called transfer rollers. Yes. Each image forming unit 16 includes a charging device 12, an exposure unit, a developing unit 13, a transfer unit, a photoconductor cleaning device 14, and a charge removal device 15 around a drum-shaped photoconductor 11. In the illustrated example, a sheet conveying belt 10 that is an endless belt is stretched between three rollers.

  The paper transport belt 10 is driven to rotate by a drive motor (not shown), and is moved by the driven rotation of the other two support rollers to be rotationally transported. At the same time, the individual image forming means 16 rotates the photoconductor 11 to form black, yellow, magenta, and cyan monochrome images on each photoconductor 11. The image for each color formed in each image forming unit 16 is sequentially transferred and superimposed on the paper transported by the paper transport belt 10 to form a composite color image on the transfer paper.

Here, each roller that supports and conveys the sheet conveying belt 10 has a predetermined eccentricity according to its processing accuracy. This eccentricity is the position of the driven roller 18 in the configuration shown in FIG. 1, even if the driven roller is driven and rotated. In the configuration shown in FIG. The belt conveyance speed fluctuates, and the density of the image called banding occurs due to the displacement of the image transfer position or the collapse of the pixel due to the speed difference with the photoreceptor at the transfer portion.
Further, in the tandem type color image forming apparatus as shown in FIG. 1, the color superimposition is shifted due to the change in the belt conveyance speed, so that the image quality is significantly lowered. Such a banding problem is not limited to the paper conveying belt shown in FIG. 1 but also in the primary transfer of the intermediate transfer belt, the exposure of the secondary transfer unit and the photosensitive belt, the development, and the transfer unit. .

The mechanism by which the eccentricity of the driven roller 18 causes the speed fluctuation at the transfer portion will be described with reference to FIG.
FIG. 2 shows the photosensitive drum 11 of the black image forming means 16 adjacent to the driven roller 18, the driving roller 17, and the driven roller. When the driven roller 18 has an eccentricity, the driven roller 18 rotates on a circle 22 with the center of rotation as 21 and the eccentric amount as a radius. At this time, the driven roller 18 rotates while passing through positions as indicated by reference numerals 18a and 18b.
The belt conveyance path when the position of the driven roller 18 is indicated by a reference numeral 18a is indicated by a solid line, and the conveyance path when the position of the driven roller 18 is indicated by a reference numeral 18b is indicated by a two-dot chain line.

  When the positions indicated by the solid line and the two-dot chain line are compared, it can be seen that the path length of the solid line, which is the conveyance path at the position indicated by reference numeral 18b, is longer. In this way, each time the driven roller 18 makes one rotation, the belt conveyance path passes through the position indicated by the two-dot chain line or the solid line, and the belt path length from the driving roller 17 to the transfer portion of the photosensitive drum 11 becomes longer or shorter. It changes suddenly.

  When viewed from the transfer section where four photosensitive drums are arranged and images are sequentially transferred onto a sheet, even if the belt is conveyed by the driving roller at a constant speed, if the driven roller 18 having eccentricity rotates, the driving roller 17 performs photosensitive. The belt conveyance path length to the transfer portion of the body drum 11 changes, and the belt conveyance amount changes by the amount the path length changes. That is, when the driven roller 18 rotates from 18a to 18b, the belt conveyance path becomes long. As a result, the belt is conveyed more in the transfer portion than the conveyance amount by the driving roller by the length that is increased. Conversely, when rotating from 18b to 18a, the belt conveyance amount decreases in the transfer portion by the amount corresponding to the shortening of the belt conveyance path.

  As described above, due to the eccentricity of the driven roller 18, the belt conveyance amount in the transfer unit varies in the rotation period of the driven roller 18, thereby causing a positional shift and a color shift.

  As a solution to the deterioration in image quality caused by the eccentricity of the driven roller, the amount of eccentricity of the driven roller at a position that affects image formation in the belt conveyance system used as the photosensitive member is affected. There has been proposed a configuration that selects and installs a roller that is smaller than the eccentric amount of other driven rollers that are not given (for example, Patent Document 1).

“Continued Fundamentals and Applications of Electrophotographic Technology” (published November 15, 1996, edited by the Electrophotographic Society, pages 35-36) JP 2003-114589 A (paragraph “Claim 1”)

However, in the configuration disclosed in Patent Document 1, by selecting a driven roller with a small amount of eccentricity, the influence on the image position shift when the amount of eccentricity is large is reduced. However, the eccentricity existing in the driven roller is reduced. It is not intended to prevent image displacement according to the amount, that is, to prevent a reduction in image quality.
Therefore, when such a technique is used, a process separate from the assembly operation of the image forming apparatus, which is the selection of the driven roller, is required, which increases the manufacturing process. Since high-precision machining without eccentricity is required, cost increases cannot be denied.

  In view of the problems in the conventional endless belt device and the image forming apparatus using the same, an object of the present invention is to provide a configuration capable of preventing the occurrence of a defective image by suppressing an increase in cost and preventing image displacement. It is an object of the present invention to provide a belt device and an image forming apparatus.

According to a first aspect of the present invention, there is provided a belt apparatus using a belt having a stretched surface that is wound around a plurality of rollers and in contact with a plurality of members between the rollers, and is hung on one of the rollers forming the stretched surface. When the belt is rotated, the surface facing the belt is aligned with the surface of the belt at the rotation position of the belt so as to contact the surface of the belt wound around the roller . A guide member having a curved surface is provided, and the roller around which the belt is wound is biased in a direction in which it is pressed against the guide member.

According to a second aspect of the invention, the belt device according to claim 1 Symbol mounting, the guide member has a surface that is characterized by being predominantly composed material having a low coefficient of friction.

According to a third aspect of the present invention, in the belt device according to the first or second aspect, a plurality of rollers or spheres are rotatably provided on a surface of the guide member that faces the surface of the belt. It is a feature.

According to a fourth aspect of the present invention, in a belt device using a belt having a stretched surface that is wound around a plurality of rollers and in contact with a plurality of members between the rollers, the belt device is hung on one of the rollers forming the stretched surface. At the position where the belt is rotated by being rotated, a guide member having a surface facing the belt wound around the roller and a curved surface shape matching the surface of the belt at the rotation position of the belt is provided. The surface of the guide member facing the surface of the belt is provided with a gas lubrication structure that blows air toward the surface of the belt .

A fifth aspect of the invention is characterized in that the belt device according to one of the first to fourth aspects is used in an image forming apparatus .

According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect , the belt is used as a photoconductor .

According to a seventh aspect of the present invention, in the image forming apparatus according to the fifth aspect , the belt is used as a sheet conveying member or an intermediate transfer member for sequentially transferring a plurality of images .

According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the fifth to seventh aspects, a belt is used as a sheet conveying or image carrier, and a driven roller that supports and rotates the belt. A control mechanism for controlling the motor of the drive shaft based on the information of the detector that detects the rotation of the roller, and from a driven roller having a detector positioned between the drive roller and the tension roller on the belt conveyance path. the portion to bend the belt conveyance path located on the driving roller side, said belt surface facing the said guide member being a curved shape matching the surface of the belt at the turning position of the belt is provided with It is a feature.

According to the first aspect of the present invention, as shown in FIG. 2, when an eccentricity is generated in one of the rollers forming the belt extending portion, the belt is changed by the change of the axial center position according to the eccentricity. of the turning position to change the belt which faces in contact with the surface of the belt, the guide member being a curved shape matching the belt surface of the turning position of the belt, the member contacting On the other hand, it is possible to prevent the load in a reduced state . In particular, when the turning position changes in the direction in which the belt extends, the roller and the belt are prevented from being displaced by the guide member, and when the turning position changes in the direction in which the belt contracts, the roller is attached. The change is prevented by being brought into pressure contact with the guide member by the force, and the turning position is always constant. Accordingly, it is possible to form a high quality image by preventing density unevenness and banding due to positional deviation of the output image.

According to the second aspect of the present invention, since the contact portion of the guide member is formed of a material having a low friction coefficient, it is possible to reduce the load on the contacting belt body and the driven roller.

According to the third aspect of the present invention, by using a rotatable structure such as a plurality of cylindrical rollers or spherical balls as the guide member, line contact or point contact is made with respect to the contacting belt body and the driven roller. The load can be reduced.

According to the fourth aspect of the present invention, by using gas lubrication at the contact portion of the guide member, it is possible to reduce the transport load without affecting the opposing belt body and the driven roller.

According to the fifth to seventh aspects of the present invention, the guide member that contacts the surface side of the belt is provided on one of the rollers forming the belt extending portion, whereby the belt turning position due to the eccentricity of the roller changes. Therefore, when a plurality of transfer portions are provided in the extended portion, it is possible to prevent the transfer start timing at each transfer portion from being shifted due to the change in the rotation position.

According to the eighth aspect of the invention, the control mechanism for controlling the motor of the drive shaft based on the information of the detector for detecting the rotation of the driven roller and the detector provided in the belt conveyance path are provided. In this case, the surface of the belt extending from the driven roller side to the driving roller side that faces the belt so as to come into contact with the belt surface from the belt surface side at the position where the belt is rotated on the driven roller side, Since the guide member having a curved shape matching the surface is provided, the change in the belt turning position can be suppressed. Thereby, the fluctuation in rotation on the driven roller side detected by the detector due to the change in the belt conveyance amount due to the change in the belt turning position is suppressed, and the fluctuation can be suppressed.

  The best mode for carrying out the present invention will be described below with reference to embodiments shown in the drawings.

In the embodiment described below, as a system for suppressing the fluctuation of the length of the belt conveyance path corresponding to the stretched surface formed by being wound around a roller or a pulley, This is a system in which one of the rollers being wound and a guide member are combined, and second, a system in which a guide member is provided in place of the roller, and the rotation position of the belt is the target in either system. The reason is as follows.
In the image forming process, the occurrence of speed fluctuation and position fluctuation of the endless belt during exposure, development, and transfer leads to a reduction in image quality.
In order to suppress the change in the belt conveyance path that causes the endless belt speed fluctuation and position fluctuation during exposure, development, and transfer, and to provide a high-quality image, the present invention wraps the belt around a conventional driven roller. As described above, the belt conveyance path, particularly the belt conveyance path length, which causes color misalignment and banding due to misalignment between images, is suppressed while having the function of regulating the belt conveyance path in any direction. I pay attention to it. Therefore, it is possible by using a structure that is adopted in these schemes, to overcome problems such as positional deviation of an image without causing a like increase in cost. A specific configuration will be described below.

The installation location of the present invention that can achieve the above object will be described in the conveyance path of an endless belt used in the image forming apparatus.
Example 1
FIG. 3 is a view showing a main part of the belt device according to the embodiment of the present invention.
The roller used in the figure is a driven roller located on the driven side among the rollers around which the belt is wound, and FIG. 3 shows only the driven roller.

Like the conventional roller, the driven roller 32 has an eccentric amount according to the processing accuracy, and the endless belt 30 is wound around the driven roller 32 in a state where the eccentric roller 30 can be eccentric. Endless belt 30, the peripheral surface of the driven roller 3 2 is in the turning position by being wound around the driven roller 3 2.
Driven roller 3 2 its shaft is made to allow smooth rotation is rotatably supported by a bearing 35.

The guide member 31 is a characteristic part of the present embodiment, and is installed so as to be in contact with the outer peripheral portion of the driven roller at a portion where the endless belt 30 is not wound at both ends of the driven roller 32 where the endless belt 30 is rotated. Has been.
The guide member 31 is fixed together with a bearing 35 to a housing side (not shown).

  A spring 34 is disposed between the driven roller 32 and the pedestal 33, and the driven roller 32 is pressed against the guide member 31 by the behavior of the spring 34. 34 is used as a pressure mechanism of the driven roller 32.

The pedestal 33 is fixed to the housing side where the guide member 31 and the bearing 35 are supported, and a spring 34 installed on the pedestal 33 pushes the bearing 35 toward the center of the guide member 31. Yes.
The bearing 35 is basically supported by the pressure mechanism and the guide member 31 described above, but the housing 35 is also shaped to be held with a certain range of motion. The movable range in this case is a range in which the driven roller 32 can move so that the driven roller 32 can come into contact with a fixed member such as the guide member 31 by the pressurizing mechanism including the spring 34. This is a range in which the portion can be held so as not to deviate greatly from the optimum position regulated by the guide member 31.
The pressure applied to the bearing 35 using the pressure mechanism is such that the position of the pedestal 33 is such that the driven roller 32 is not separated from the guide member 31 even if the conveyance load of the endless belt occurs during actual operation of the image forming apparatus. And the spring 34 are selected. In this way, by installing the guide member on the outer periphery of the driven roller that regulates the belt conveyance path of the driven roller 32, the position fluctuation of the outer circumference that regulates the belt conveyance path even if the driven roller has eccentricity. And the change in the belt conveyance path length due to the eccentricity of the driven roller can be prevented.

  In addition, since the guide member 31 is provided at the end of the driven roller 32 where the endless belt is not wound, the belt body does not directly act, so that the belt body may be damaged or wrinkled. There is no. In addition, the guide member can also have a function as a guide member for preventing the endless belt body from meandering.

  The arrangement of the guide members is not limited to being provided at the end of the driven roller 32 as shown in FIG. 3, and for example, the configuration shown in FIG. 6 may be employed. In FIG. 6, the guide member 61 is installed on the belt body 30. The driven roller 32 is in pressure contact with the guide member 61 with the belt body 30 interposed therebetween.

  The guide member 61 is not limited to two at both ends, and a plurality of guide members 61 may be provided. Further, the same belt conveyance path length change prevention effect can be obtained with one member having a width in the depth direction (corresponding to the axial direction of the driven roller 32), such as the guide member 62 shown in FIG. 6B. .

  The advantage of the arrangement shown in FIG. 6 is that downsizing of the apparatus is an important market need now, and guide members can be installed without increasing in the roller axis direction (depth direction). Is possible. In addition, the endless belt is provided with a detent member at the end of the belt in order to prevent the so-called meandering phenomenon of the belt itself in the belt width direction. The length of is often shorter than the belt width. Guide members 61 and 62 can also be installed on such a roller.

The guide members shown in FIGS. 3 and 6 are set with the installation method and material described below.
FIG. 5 shows the guide members indicated by reference numeral 31 in FIG. 3 and reference numerals 61 and 62 in FIG.
In FIG. 5, the guide member denoted by reference numeral 51 has a contact surface 52 in contact with the driven roller or the endless belt body, which has a curved surface shape that matches the circumferential shape of the driven roller and the surface when the belt body is wound thereon. Has been.
The purpose of this curved surface shape is not a great resistance against the rotation of the driven roller and the conveyance of the endless belt. In addition, the wear of the guide member is to provide wear resistance to other components of the belt conveyance system so that the guide member is not frequently replaced. That is, if the member has high wear resistance, the range of the contact surface 52 may be narrow and the resistance may be reduced. The shape of the surface 51 other than the surface 52 in contact with the driven roller or the belt body, for example, may be any shape, and the shape is determined so as to be easily fixed to a housing (not shown). However, the end portions of the curved surface 52 that are in contact with each other as indicated by reference numerals 53 and 54 in FIG. Good. The material of the guide member, particularly the contact surface 52, is preferably made of a material having a low coefficient of friction with respect to the driven roller and endless belt that come into contact. Generally, for a metal driven roller, a polyacetal (POM) or polyamide (PA) layer is provided on the contact surface 52. Alternatively, a fluororesin coating such as polyratrafluoroethylene (PTFE) may be applied. Although the guide member may be composed only of these materials having a low friction coefficient, it is necessary to ensure the rigidity of the entire guide member. When the rigidity of the guide member is low, the belt conveyance path length changes due to the deformation of the guide member. It is desirable to have a shape that ensures rigidity so that the guide member does not deform, or a guide member that has a surface layer made of a material having a low coefficient of friction on a base of metal or hard resin. The object here is deformation and wear that occur within the time of outputting the image. Long-term deformation and wear are allowed because the influence on the image is very small.

Next, the location for installing the guide member on the driven roller will be described with reference to FIG.
FIG. 4 is a view of the driven roller 32 seen from the side, and an endless belt body 30 is wound around the driven roller 32.
In FIG. 4, a point at which the endless belt 30 starts to be wound around the driven roller 32 is indicated by reference numeral 40, and a point away from the driven roller 32 is indicated by reference numeral 41.
The angle θ of the driven shaft formed by the points 40 and 41 is called a belt winding angle.
The most effective way to suppress the belt conveyance path change due to the eccentricity of the driven roller is to suppress the fluctuation in the position of the outer peripheral surface at the point of the central portion 42 of the belt winding angle. The guide member 31 is installed at this position to suppress the position fluctuation of the outer peripheral surface of the driven roller 32. Alternatively, as indicated by reference numeral 45 in FIG. 4B, the guide member may be installed in a plurality of points within the winding range of the endless belt 30. By installing at a plurality of locations, it is possible to stably regulate the outer peripheral surface of the driven roller.

  In this embodiment, the guide member 31, 45, 61 or 62 can be used to prevent the belt conveyance path length from being changed due to the eccentricity of the driven roller 32. Therefore, it is not necessary to increase the processing accuracy of the driven roller, and the cost is high. An accurate belt conveyance system can be realized. In addition, the accuracy of the driven roller only needs to have a roundness on the outer periphery so that a large gap is not generated between the guide member and the tolerance for the eccentricity becomes very large. Can be lowered.

The following structure can be used as another structure of a guide member.
As a means for realizing low friction with respect to the driven roller and the endless belt on the contact surface indicated by reference numeral 52 in FIG. 5, a lubrication method may be used. Generally, it is realized by applying a lubricant such as grease. However, as shown in FIG. 1, applying grease on the surface of an endless belt used in the image forming apparatus or in the vicinity thereof, drives the image or the endless belt. It will adversely affect performance.

In the present embodiment, a gas lubrication method is used in consideration of solving the above-described problems.
In FIG. 7, the contact surface 70 of the guide member is processed with a helical bone groove 71 that realizes gas lubrication. The width, installation interval, inclination and the like of the helical bone groove 71 are determined by the speed of the driven roller and the endless belt body. By this process, the driven roller and the endless belt pressed against the guide member are smoothly rotated and conveyed.
Further, as a method using the same gas lubrication, as shown in FIG. 8, there is a method in which a vent hole 81 is provided in the guide member 82 and air is blown from the back side 83 toward the contact surface 80. Such a configuration, by using the words gas lubrication, it is possible to restrict the change of belts conveying path length without affecting the belt surface of the belt conveying system used in the image forming apparatus.

Further, as a modified example of the configuration for suppressing the length of the conveyance path of the endless belt that is wound around the driven roller, a guide member using a bearing may be used.
FIG. 9 shows an example of a guide member using a bearing. The guide member 90 has a ball 92 held by a holder 91. The belt conveyance path is regulated in such a manner that the balls 92 are in point contact with the driven roller or the endless belt body on the contact surface 93. The ball 92 may be a cylindrical roller. In this case, each cylindrical roller is in line contact with the driven roller or the belt body. Since the guide member has a bearing structure, very low friction is realized. The number of balls 92 and cylindrical rollers constituting the bearing may be one or plural.
In the case of a small number, for example, one, the belt conveyance path change is determined by the processing accuracy of the ball, so that high accuracy is required. On the other hand, when a plurality of balls or cylindrical rollers are used, the required accuracy is lower than in a single case. This is because the contribution rate of one processing accuracy is lowered because the plurality of balls or cylindrical rollers are in contact with the driven roller or the endless belt.

According to the embodiment as described above, the fluctuation in the belt conveyance path length due to the eccentricity at the driven roller that is the turning position around which the endless belt is wound is suppressed by the guide member. The occurrence of color misregistration and banding due to the misalignment of the transfer positions of the images due to the fluctuations of the image can be prevented and the occurrence of defective images can be reliably prevented. In addition, when the guide member is used, an increase in resistance at the contact surface can be suppressed by the lubrication mechanism or the contact mechanism, so that the intended purpose described above can be achieved while suppressing an increase in processing cost and component cost.
(Example 2)
The present embodiment is characterized in that the driven roller is constituted by a guide member instead of installing the guide member facing the driven roller.
FIG. 10 shows a configuration in which a guide member is provided instead of the driven roller to regulate the belt conveyance path.

Both ends of the guide member 101 or a portion where the belt is not in contact are fixed to a housing that supports and fixes a driving roller, other driven rollers, and the like of a belt conveyance system (not shown).
A portion 103 where the endless belt of the guide member 101 contacts is a curved surface having a certain curvature so that the endless belt smoothly moves on the surface. The curvature may be partially changed so that the endless belt begins to contact the guide member 101 and the belt is likely to enter.

  In this embodiment, by providing a guide member instead of the driven roller, the cost of manufacturing the driven roller can be greatly reduced while regulating the transport path of the endless belt, which is a function of the conventional driven roller. it can. Further, since there is no belt path length variation due to the eccentricity of the driven roller, highly accurate belt conveyance is realized.

  The guide member 101 desirably has low friction with respect to the endless belt. Here, as in the first embodiment, a polyacetal (POM) or polyamide (PA) layer is provided on the contact portion 103 of the guide member 101. Alternatively, a fluororesin coating such as polyratrafluoroethylene (PTFE) may be applied. Further, a system using a helical bone groove or gas injection as shown in FIGS. 11 and 12 using gas lubrication may be used. Incidentally, reference numeral 110 in FIG. 11 denotes a guide member, and reference numeral 111 denotes a helical bone groove. Moreover, 121 of FIG. 12 is a guide member and has shown 120 gas injection directions.

  Similarly, a bearing mechanism as shown in FIG. 13 may be used. 131 denotes a ball or cylindrical roller, 132 denotes a cage, 130 denotes a guide surface, and 133 denotes an outer shape of the guide member. By adopting the low friction coefficient surface or the low friction mechanism shown in FIGS. 11, 12, and 13 for the entire guide member or a part thereof, it becomes possible to suppress the conveyance resistance of the endless belt, An efficient belt conveyance path can be realized without causing belt vibration.

Furthermore, as shown in FIG. 14, a configuration in which a cylindrical ring 141 is provided between the guide member 140 and the endless belt may be employed. In this configuration, the guide member 140 is configured to realize low friction with respect to the endless belt described above, and the cylindrical ring 141 contacts the endless belt and rotates while sliding with the guide member 140 while interlocking.
The guide member having each configuration that achieves low friction can achieve low friction that is equal to or higher than that of metal. Further, the endless belt material varies depending on the image forming apparatus. That is, even in the image forming apparatus having the same configuration, a belt material that is different depending on conditions such as toner, development, and transfer is selected. Accordingly, it is necessary to select the configuration and material of the guide member that realizes low friction.

However, the configuration shown in FIG. 14 is for the cylindrical ring regardless of the material of the endless belt, so that selection is not necessary. Furthermore, the cylindrical ring has an effect of stably holding the endless belt even when the guide member is provided only at both ends, or when each configuration realizing low friction is scattered on the guide member.
(Example 3)
This embodiment is characterized by the installation position of the guide member on the belt conveyance path.
The configuration of the guide member described in the first and second embodiments will be described as to which of the driven rollers provided to regulate the belt path set on the belt conveyance path.
This will be described using the generalized belt conveyance path shown in FIG. The transport system of the endless belt 151 in FIG. 15 includes a driving roller 150, one tension roller 154 that applies tension to stably transport the belt, and four driven rollers 152, 153, and 155 that regulate the belt transport path. 156. The rotational direction of the driving roller and the conveying direction of the endless belt are also shown. Further, the belt conveyance path regulated by the driving roller, the driven roller, and the tension roller is divided for each roller, and the respective conveyance sections are denoted by A to F. Each of the four driven rollers has an eccentricity, and the belt conveyance path changes with the rotation period of the driven rollers. This path change is absorbed by the movement of the tension roller 154. This absorption operation is because the tension roller 154 applies a constant tension to the belt for stable belt conveyance. For example, when the belt path length increases due to the eccentricity of the driven roller, the tension of the belt increases, so that the tension roller moves in the direction of shortening the belt path to keep the belt tension constant.

In each of the belt conveyance sections A to F, it will be described whether the eccentricity of the driven roller affects the belt conveyance.
First, in the section A, the belt conveyance amount is governed by the belt conveyance amount sent out by the driving roller 150 and is not affected by the belt path change due to the eccentricity of the driven roller. Next, in the section B, it fluctuates due to the influence of the path change due to the eccentricity of the driven roller 152 by the amount by which the belt of the driving roller 150 is sent out. That is, in the section B, it is necessary to suppress the influence of the eccentricity of the driven roller 152.

  Similarly, in section C, the driven rollers 152 and 153 are affected by the eccentricity. However, in terms of whether or not the influence of the path change due to the eccentricity of the driven rollers 152 and 153 also appears in the section D, the path change of the driven rollers 152 and 153 is absorbed by the movement of the tension roller 154, and thus is not affected. Absent. In the section F, the belt conveyance amount is governed by the belt conveyance amount drawn by the driving roller 150 and is not affected by the belt path change due to the eccentricity of the driven roller.

  Next, in the section E, the driving roller 150 is affected by the path change of the driven roller 156 by the amount by which the belt is pulled. In other words, in section E, measures are necessary because it is affected by the eccentricity of the driven roller 156. Similarly, in section D, the driven rollers 156 and 155 are affected by the eccentricity. However, this effect is the same as before and does not propagate to section C.

  Based on the above, when there are an exposure unit, a development unit, and a transfer unit in the belt conveyance section B, a guide member is provided at the location of the driven roller 152. Further, when the belt conveyance section C includes an exposure unit, a development unit, and a transfer unit, guide members are provided at the positions of the driven rollers 152 and 153.

  When the belt conveyance section E includes an exposure unit, a development unit, and a transfer unit, a guide member is provided at the location of the driven roller 156. Further, when the belt conveyance section D includes the exposure unit, the development unit, and the transfer unit, guide members are provided at the positions of the driven rollers 156 and 155.

FIG. 16 shows a specific example of the installation configuration in each section, and details will be described below.
The four photosensitive drums 161 form images of different colors such as cyan, magenta, yellow, and black, respectively. The transfer belt 162 is conveyed in the direction of the arrow by the rotation of the driving roller 160. The tension roller 166 applies a certain tension to the transfer belt.

  The images formed on the respective photosensitive drums are sequentially transferred directly to the sheet 169 carried by the transfer belt 162 with the vicinity of the driven roller 168 as an entrance, and are carried out with the vicinity of the driven roller 165 as an exit. Thereafter, the color image superimposed by a fixing device (not shown) is fixed and output from the image forming apparatus.

On the transfer belt unit in FIG. 16, there is a transfer portion in the belt conveyance section where the photosensitive drums 161 are arranged. Considering the positional relationship between the driving roller 160 and the tension roller 166, the number of driven rollers 165 that affect the belt conveyance of the transfer unit is 165.
If the driven roller 165 is eccentric, the path length change due to the eccentricity of the driven roller 165 occurs due to the belt conveyance amount of the driving roller 160, and the belt conveyance at the transfer unit varies. Therefore, the driven roller 165 guide member is installed.

In addition, as a conventionally known technique, a rotary encoder is installed on the driven roller to control the drive motor feedback in order to control the belt conveyance speed fluctuation at the transfer unit due to the eccentricity of the drive roller and the load fluctuation at the time of paper entry. There is technology. This is intended to convey the belt at a constant speed by controlling the roller that rotates following the belt to rotate at a constant speed.
For example, when a rotary encoder is installed on the driven rollers 165 and 168 in FIG. 16, the belt conveyance fluctuation of the transfer unit can be detected by the rotary encoder installed on these shafts, and feedback control can be performed. However, when the rotary encoder is installed at the shaft of the driven roller 167, there is a possibility that the rotation fluctuation is detected due to the influence of the path change due to the eccentricity of the driven roller 168 on the belt conveyance amount of the transfer unit. .

  If this fluctuation is also feedback controlled, it is different from the speed fluctuation occurring at the transfer section, and therefore, erroneous control occurs and a new fluctuation occurs. That is, when the rotary encoder is installed on the driven roller 167, it is necessary to install a guide member on the driven roller 168 in order to suppress fluctuations in erroneous detection.

  In this embodiment, the case of direct transfer onto the paper has been described. However, both transfer sections are also used in the intermediate transfer system in which the image is transferred onto the temporary transfer belt (primary transfer) and then transferred onto the paper (secondary transfer). In the same manner as described above, a guide member can be installed in the driven roller portion to suppress the transfer position shift due to the influence of the path change due to the eccentricity of the driven roller.

1 is a schematic diagram of an image forming apparatus to which a belt device according to an embodiment of the present invention is applied. It is a figure for demonstrating the malfunction which generate | occur | produces in the belt apparatus shown in FIG. It is explanatory drawing the principal part of the belt apparatus by a 1st Example. It is a figure for demonstrating the installation structure of the guide member used for the principal part shown in FIG. 3, (A) has shown the example, (B) has shown the other example, respectively. It is a figure for demonstrating the structure of the contact surface in the guide member used for the Example shown in FIG. It is a figure for demonstrating the principal part modification of the Example shown in FIG. It is a figure for demonstrating the structure of the contact surface of the guide member used for the structure shown in FIG. 3 and FIG. It is a figure which shows the other example of the contact surface shown in FIG. It is a figure which shows another example of the contact surface shown in FIG. It is a figure which shows the principal part of the belt apparatus by the 2nd Example, (A) has shown the whole structure, (B) and (C) have each shown the state of side view. It is a figure which shows an example of a structure of the contact surface of the guide member used for the principal part shown in FIG. It is a figure which shows the other example of a structure of the contact surface of the guide member used for the principal part shown in FIG. It is a figure which shows another example of a structure of the contact surface of the guide member used for the principal part shown in FIG. It is a perspective view which shows the other modification of the guide member shown in FIG. It is a figure for demonstrating the installation structure of the guide member in the belt apparatus by the 3rd Example. It is a figure which shows the specific content regarding the installation structure demonstrated in FIG.

Explanation of symbols

30 Belt 31, 61, 62, 101 Guide member 52, 70, 80, 93 Contact surface 92, 131 Ball

Claims (8)

In a belt device using a belt having a stretched surface that is wound around a plurality of rollers and in contact with a plurality of members between the rollers,
At the position where the belt rolls by being wound around one of the rollers forming the stretched surface, a surface facing the belt is in contact with the surface of the belt wound around the roller, A guide member having a curved shape matching the surface of the belt at the turning position of the belt is provided;
The belt device, wherein the roller around which the belt is wound is urged in a direction in which the roller is pressed against the guide member. The belt device according to claim 1, wherein
The belt device is characterized in that the guide member is mainly composed of a material having a low friction coefficient on the surface. The belt device according to claim 1 or 2,
A belt device, wherein a plurality of rollers or spheres are rotatably provided on a surface of the guide member that faces the surface of the belt. In a belt device using a belt having a stretched surface that is wound around a plurality of rollers and in contact with a plurality of members between the rollers,
At the position where the belt rolls by being wound around one of the rollers forming the stretched surface, the surface facing the belt wound around the roller is the surface of the belt at the belt turning position. A guide member having a curved surface shape is provided.
A belt device characterized in that a gas lubrication structure for blowing air toward the surface of the belt is provided on a surface of the guide member that faces the surface of the belt.   An image forming apparatus using the belt device according to claim 1. The image forming apparatus according to claim 5.
An image forming apparatus, wherein the belt is used as a photoreceptor. The image forming apparatus according to claim 5.
The image forming apparatus, wherein the belt is used as a sheet conveying member or an intermediate transfer member for sequentially transferring a plurality of images. The image forming apparatus according to claim 5 ,
The belt is provided with a control mechanism that controls the motor of the drive shaft based on information from a detector that detects the rotation of a driven roller that rotates while supporting the belt. The surface facing the belt is a curved surface that matches the surface of the belt at the rotation position of the belt at a position where the belt conveyance path located on the drive roller side is bent from a driven roller having a detector positioned between the rollers. An image forming apparatus comprising the guide member having a shape.

Images