JP2003246483A - Tension applying mechanism and image forming device provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the drawing force of offset movement and meandering movement of an endless belt by keeping the tension of the endless belt almost constant with low-cost constitution even when the circumferential length of the endless belt changes. <P>SOLUTION: A tension roller 34 is rotatably supported to the tip of an arm member 40 swingable around a rotating shaft 41, and the arm member 40 is energized by a tension spring 35. A distance from the rotating shaft 41 to the action line α of the tension spring 35 is short when the circumferential length of the belt 30 is short (a), and long when the circumferential length of the belt 30 is long (c), so that moment Ma is large in the former, and moment Mb is small in the latter. The longer the circumferential length of the belt 30 is, the larger energization load is. Tension T is thereby almost constant regardless of the length of the belt 30. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tension applying mechanism for applying a tension to an endless belt wound around a plurality of rollers, and an image forming apparatus having the same.

[0002]

2. Description of the Related Art Conventionally, among image forming apparatuses which employ an electrophotographic system or an electrostatic recording system in an image forming process, there is one which uses a cylindrical photosensitive drum as an image carrier.
It is well known that peripheral units such as a charger, an exposure unit, a developing unit, a cleaning unit, a recording material conveying mechanism (recording material conveying unit), etc. are arranged around the photosensitive drum.

By the way, in recent years, in order to further improve the functions of the image bearing member, the recording material conveying mechanism, etc., a photosensitive belt constituted by an endless belt is adopted as the image bearing member instead of the photosensitive drum. Alternatively, an image forming apparatus has been developed which employs a conveyor belt composed of an endless belt as a recording material conveying mechanism.

In the image forming apparatus using such an endless belt, many functions can be improved, but in order to improve the durability and belt running performance of the endless belt. A means for suppressing slip of the endless belt during driving, deviation of the endless belt from the reference trajectory, and meandering is indispensable.

Here, as one of the factors of the positional deviation due to the slip of the endless belt or the one-sided movement, there are variations (nonuniformity) in the belt tension and imbalances at both ends.

The variations and unbalances in the belt tension are dimensional variations of the endless belt (manufacturing dimensional variations) and changes in the belt dimensions (belt shrinkage and contraction due to the environment in which the belt driving device is used, the temperature rise in the device, and changes over time). Due to the difference in the belt circumference due to the dimensional change of the endless belt due to expansion, etc., and the precision of parts such as the roller that stretches the belt and the frame of the belt drive device that supports the roller. There are factors that occur. However, there is a limit to increase the dimensional accuracy and the like, and if the accuracy is further improved, it also leads to an increase in the cost of the apparatus itself.

Therefore, conventionally, the following method has been adopted as a means for correcting these problems when the endless belt is slipped, biased or meandered due to variations or imbalances in the belt tension.

A belt deviation prevention guide is provided at the end of the back surface of the belt.

As a mechanism for applying tension to the belt, there are many types in which the tension roller holding member is slidable only in the belt tension applying direction and is biased by a compression torsion coil spring or the like. There is no effective countermeasure against uneven belt tension.

When slip, deviation or meandering of the endless belt occurs, the biasing force applied to the belt is sufficiently strengthened against slip to prevent it. In addition, for deviation or meandering, the belt deviation control guides provided at both ends of the inner peripheral surface of the endless belt abut on the belt deviation restriction member provided at the side end of the driven roller that stretches the endless belt. Some are arranged to let you. By contacting the belt deviation regulation guide of the endless belt with the belt deviation regulation member of the driven roller, deviation of the endless belt is regulated when the endless belt rotates. The belt deviation regulating member is joined to the end portion of the back surface of the endless belt by adhesion, sewing or the like.

A method of equalizing the belt tensions at both ends of the endless belt. This is to use an arm type holding member as the tension roller holding member and to use a center member as a means for keeping the belt tension applied to both ends of the endless belt always constant. A shaft in the balance state with one fulcrum is added to the shaft, and both ends of the shaft are hooked between the balance shaft with tension and torsion coil springs, which are biasing means, and the tension roller holding member. It is designed to equalize the belt tension of. The belt deviation regulating guide is brought into contact with the belt deviation regulating member in the same manner as for the regulation of slight belt deviation and meandering which occur even if the belt tension is equalized.

[0012]

However, the above-mentioned conventional method has the following problems.

That is, in the conventional method as described above, as shown in FIG. 5, the biasing member 44 and the tension roller holding member do not always have a uniform belt tension. Therefore, in the case where the endless belt size varies due to manufacturing, or when the endless belt size changes due to the use environment or changes with time, FIG.
As shown in (a), (b), and (c), the conveyor belt 30 traveling in the direction of arrow A is in a state (a) where the belt tension T is large or a state (c) where the belt tension T is small.

The conveyor belt 30 wound around the rollers 31, 32, 33 and 34 is moved by the urging member 44 to the roller 34.
The urging load G urges through the
The size of is constant when the belt circumference is long (c), short (a), and intermediate (b). Therefore, the belt tension T is large when the belt circumferential length is long, small when the belt circumferential length is short, and becomes a size between these when the belt circumferential length is intermediate.

As described above, when the belt circumference changes, the belt tension T applied to the belt also changes.

Note that, among the reference numerals in FIG. 5, those not described are the same as those in FIG. 1 in Embodiment 1 described later, and therefore will be described in FIG.

Further, if there is a difference in circumferential length between both ends of the belt in one belt, a difference in belt tension occurs between the one end and the other end, so that the difference in the belt tension occurs in one belt. Belt tension is not uniform (tension unbalance). Further, it is necessary to apply an excessively strong belt tension in order to suppress the occurrence of belt slip. As a result, the moving force of the one-sided movement and the moving force of the meandering while the belt is running, that is, the so-called deviating force becomes large, and a large force is required to regulate the one-sided movement and the meandering movement of the belt.

Further, in the above-mentioned method, when there is a difference in circumferential length between both ends of the belt in one belt, the difference in the belt tension between one end and the other end (tension annulus). (Balance) is canceled by the equalizing mechanism, but it occurs when there are variations in the circumferential length of multiple endless belts during belt manufacturing, or when there are dimensional changes due to use environment or changes over time. There are things that are strong or weak. "You can't cancel the problem.
As a result, it is necessary to increase the belt tension more than necessary to prevent the belt from slipping. Similarly, the deviation force of the deviation movement and the meandering movement during the running of the belt becomes large, and the deviation movement and the meandering of the belt are increased. A great deal of force is needed to regulate movement.

As a result, a large frictional force acts between the side surface of the belt deviation regulating guide and the belt deviation regulating member, and the vicinity of the joint surface between the endless belt and the belt deviation regulating guide, the belt deviation regulating member, and the belt deviation regulating guide. The durability will drop sharply, and the deviation control guides provided at the end of the back surface of the endless belt will easily get over the deviation control members provided at the end of the driven roller, which will make the running of the endless belt unstable and, as a result, endless. There is a problem that the belt is broken or the durability of the belt drive device is not improved. Further, in the method of (1), it is necessary to add parts by the equalizing mechanism, which causes an increase in cost of the device.

The present invention has been made in view of the above problems, and it is a simple and inexpensive structure that the belt tension applied to the endless belt is always kept constant even if the endless belt has dimensional variations or dimensional changes. It is also possible to provide a belt drive device and an image forming apparatus including the belt drive device, which enables high durability and high stability by reducing the offset force of the endless belt that shifts to one side or to meander. It is what

[0021]

The invention according to claim 1 is
In a tension applying mechanism for applying a tension to an endless belt wound around a plurality of rollers, a tension roller abutting on the endless belt, a swingable arm member rotatably supporting the tension roller, and An urging member that urges the arm member to press the tension roller against the endless belt, and the rotational moment applied to the tension roller by the urging member via the arm member is equal to that of the endless belt. The longer the circumference, the larger
The arm member and the urging member are arranged.

According to a second aspect of the present invention, in the tension applying mechanism according to the first aspect, a line connecting the rotation center of the tension roller and the swing center of the arm member and a line of action of the urging member. The arm member and the urging member are arranged such that the angle formed by the endless belt becomes larger as the circumferential length of the endless belt becomes longer.

According to a third aspect of the present invention, in the tension applying mechanism according to the second aspect, the arm member and the urging member, which act individually, are arranged at both ends of the tension roller in the longitudinal direction. It is characterized by

The invention according to claim 4 relates to claims 1 to 3.
In the tension applying mechanism of any one of the above,
It is characterized in that the arm member is composed of a resin component integrally molded with a resin material having good slidability.

According to a fifth aspect of the present invention, in an image forming apparatus including an image forming section for forming an image on a recording material and an endless belt, the endless belt is any one of the first to fourth aspects. The endless belt according to item 1 above.

According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the endless belt is a photosensitive belt on the surface of which a toner image is formed.

According to a seventh aspect of the invention, in the image forming apparatus according to the fifth aspect, the endless belt is an intermediate transfer belt to which an image formed on an image carrier is transferred. To do.

The invention according to claim 8 is the tension applying mechanism according to claim 5, wherein the endless belt carries and conveys a recording material onto which an image formed on an image carrier is transferred. It is characterized by

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In addition, in each of the drawings, components denoted by the same reference numerals have similar configurations or actions, and repeated description thereof will be appropriately omitted.

<First Embodiment> FIG. 1 shows an example of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG.
FIG. 1 is a laser beam printer of an electrophotographic system, and FIG. 1 is a vertical sectional view showing its schematic configuration.

A laser beam printer (hereinafter referred to as "image forming apparatus") 100 shown in FIG. 1 has four image forming sections, namely, yellow, cyan, magenta, and black, inside an image forming apparatus main body 101. Image forming units A, B, C, and D for forming toner images (images) are provided.

Photosensitive drums 1a, 1b, 1c and 1 as image bearing members are provided in the image forming sections A, B, C and D, respectively.
d, charging rollers 2a, 2b, 2c, 2d, scanner units (exposure devices) 3a, 3b, 3c, 3d, developing device 4
a, 4b, 4c, 4d, transfer rollers 6a, 6b, 6c,
6d, cleaning devices 7a, 7b, 7c, 7d and the like are provided.

In the image forming units A, B, C, D, the four photosensitive drums 1a, 1b, 1c, 1 whose surfaces are uniformly charged by the charging rollers 2a, 2b, 2c, 2d.
An electrostatic latent image is formed on the surface d of the scanner units 3a, 3b, 3c, and 3d by being irradiated with light according to image information. These electrostatic latent images are
The developing sleeves 5a, 5b, 5c and 5d provided on the developing units 4a, 4b, 4c and 4d respectively cause yellow,
Cyan, magenta, and black color toners are attached and developed as a toner image.

On the other hand, the recording material P such as paper is stored in the paper feed cassette 1.
It is accommodated in the first unit, is fed by the paper feed roller 12, is separated into one sheet by the retard roller pair 13, and is conveyed to the registration roller pair 14. Further, the recording material P manually fed from the manual paper feeding unit 15 is carried to the registration roller pair 14 by the carrying roller 16.

The recording material P conveyed from the paper feed cassette 11 or the manual paper feed section 15 is supplied by the registration rollers 14 to a conveyor belt 30 formed in an endless form and carried on the surface thereof ( Is adsorbed). The recording material P is carried on the conveyor belt 30, and then sequentially conveyed to a transfer portion formed between the photosensitive drums 1 a, 1 b, 1 c, 1 d and the conveyor belt 30.

In the present embodiment, the conveyor belt 30 is made of a film-like member having a volume resistivity of, for example, 10 ¹² Ω · cm or less and a thickness of about 150 μm. Here, this volume resistivity is determined by JIS method K691.
ADVANTEST using the measurement probe according to 1.
It is a value obtained by applying 100 V with a high resistance meter R8340 manufactured by the same company.

As shown in the figure, the conveyor belt 30 includes a driving roller 32, a belt deviation regulation driven roller (hereinafter referred to as "regulation roller") 31 provided on the upstream side of the driving roller 32, and a downstream side of the driving roller 32. It is driven while being stretched by a belt driving means 100B provided with a driven roller 33 and a tension roller 34 provided on the side, and is rotated in the direction of arrow A (counterclockwise).

Incidentally, these rollers 31, 32, 33,
34 are all belt drive means 10 at both ends.
It is rotatably held by a bearing provided on a main body frame (not shown) of 0B and is arranged so as to be substantially parallel to each other.

Here, the driving roller 32 is composed of a metal roller having a rubber layer having a large friction coefficient on the surface layer and has a diameter set to about 30 mm. The driving roller 32 is set in a predetermined direction in the direction of arrow A in FIG. It is designed to be rotated at a speed. The driven roller 33 is, for example, SUS.
It is composed of a metal roller such as (stainless steel), and its both end bearings are fixed at predetermined positions.

On the other hand, as shown in FIG. 2, which is a partially cutaway perspective view, the regulation roller 31 has, at both ends thereof, a belt deviation for regulating defects such as deviation and meandering that have occurred in the conveyor belt 30. Regulation member (hereinafter simply referred to as "regulation member")
36 and 37 are attached.

The restricting members 36 and 37 are concentrically rotatably provided between the restricting roller 31 and a bearing (not shown) that supports the shaft of the restricting roller 31 as shown in FIG. The inner end surface thereof is in contact with the side end surface of the regulation roller 31 and is formed to have substantially the same diameter as the regulation roller 31.

When the conveyor belt 30 is displaced or meandered, the restriction guides 3 are provided on the side surfaces of the restriction members 36 and 37 at both ends of the inner peripheral surface of the conveyor belt 30.
8, 39 are abutted and guided.

The material of the regulating members 36, 37 is preferably one having a low friction coefficient, and for example, a material having good slidability such as POM is used. The material of the regulation guides 38, 39 is a rubber material having a low frictional stress and capable of withstanding the bending stress received while being wound around the rollers 31, 32, 33, 34 which are belt tension rollers. Is used.

By the way, such regulating members 36, 37
As shown in FIG. 1, the regulation roller 31 provided with is arranged so that the winding angle of the conveyor belt 30 is the largest as compared with the other rollers 32, 33, 34. By maximizing the wrapping angle in this way, the contact area between the regulation members 36, 37 and the regulation guides 38, 39 can be increased, and the conveyor belt 3 having a large offset force.
The deviation of 0 can be regulated.

Further, the tension roller 34 is provided with a tension spring (tensile coil spring) 3 via the arm member 40.
5 is always urged in the direction in which the conveyor belt 30 is stretched, and the wrap angle of the conveyor belt 30 is different from that of the other rollers 3.
1, 32, and 33 are arranged so as to be the smallest. In the present embodiment, the tension roller 34 is arranged on the upstream side of the regulation roller 31 along the rotation direction of the conveyor belt 30.

In the present embodiment, the tension roller 34 is rotatably supported by the arm member 40, and the arm member 40 is swingably supported, and at the same time, a tension spring (urging force) as a biasing means. (Member) 35. As a result, the tension roller 34 is brought into contact with the back side of the conveyor belt 30 to apply tension to the conveyor belt 30. In the present embodiment, the tension roller 34, the arm member 40, and the tension spring 35 constitute a tension applying mechanism.

As shown in FIG. 3, the arm member 40 rotatably supports the tension roller 34 on the base end side, and the rotary shaft (swing center) 41 is provided on the base end side. . A locking portion 43 to which one end portion (front end portion) of the tension spring 35 is connected is formed between the front end side and the base end side of the arm member 40. This tension spring 3
The locking portion 42 to which the other end portion (base end portion) of 5 is connected,
It is provided on the body frame (not shown) of the belt driving means 100B. In FIG. 3, the arm member 4
Although 0 and the like are shown only at one end of the tension roller 34, the same arm member 40 and tension spring 3 are also provided at the other end of the tension roller 34.
5 are provided.

The tension spring 35 has a low spring constant, and the rotation shaft 41 of the arm member 40 is arranged near the back surface of the conveyor belt 30 to shorten the circumference of the conveyor belt 30. Regardless, conveyor belt 3
It can be configured so that substantially the same tension acts on 0.

Details will be described below with reference to FIGS. 4 (a), 4 (b) and 4 (c). In FIG. 4, when the acting direction (line of action) of the spring of the tension spring 35 is α, and the line connecting the rotation axis (swing center) 41 of the arm member 40 and the center (rotation center) of the tension roller 34 is β 4 (c), when the peripheral length of the conveyor belt 30 is long, the angle formed by α with respect to β is large, and as shown in FIG. 4 (a), the peripheral length of the conveyor belt 30 is short. In this case, the positional relationship between the tension spring 35 and the arm member 40 is set so that the angle formed by α with respect to β becomes small. In other words, the arm member 40 is increased in proportion to the increase in the circumferential length of the conveyor belt 30.
The tension spring 35 and the arm member 40 are arranged so that the distance from the rotation shaft 41 to the line β becomes long.

By arranging the tension spring 35 and the arm member 40 in this way, the rotational moments Ma, M of the tension roller 34 increase as the circumference of the conveyor belt 30 increases.
b and Mc become large (Ma <Mb <Mc).

As a result, when the circumference of the conveyor belt 30 is short as shown in FIG. 4A (= when the winding angle of the conveyor belt 30 with respect to the tension roller 34 is small), the tension is higher than that in FIG. 4B. By reducing the rotation moment M of the roller 34, the tension T acting on the conveyor belt 30 can be made equal to that in FIG. 4B.

Further, as shown in FIG. 4C, the conveyor belt 30
4 is long (= when the winding angle of the conveyor belt 30 with respect to the tension roller 34 is large),
The rotation moment M of the tension roller 34 is larger than that of (b).
By increasing the value, the tension T acting on the conveyor belt 30 can be made equal to that in FIG.

Thus, as the circumference of the conveyor belt 30 increases, the rotational moment M of the tension roller 34 increases correspondingly (Ma <Mb <Mc), and the urging load G is increased.
Also grows. By increasing the biasing load G and increasing the circumferential length of the transport belt 30, the tension acting on the transport belt 30 can be kept substantially constant even when the circumferential length of the transport belt 30 changes. .

Due to the arrangement of the tension spring 35 and the arm member 40 as described above, there are variations in the circumferential length and a difference in the circumferential length between the individuals due to the difference in the conveyor belt 30,
Even if the peripheral length changes due to contraction / expansion due to temperature rise in the image forming apparatus main body 101, it is possible to constantly apply a constant tension T to the conveyor belt 30.

Further, when a comparative experiment was actually conducted on the durability of the belt driving device 100B, it was found that the belt driving device 100B according to the present embodiment was able to reduce the peripheral length among the manufacturing variations, or the manufacturing variations. Among them, even when there is a large difference in the left and right circumferences of the belt, or even when the circumference of the conveyor belt 30 contracts in a low temperature environment, stable running for 300 hours or more was obtained, whereas the conventional belt drive device
The transfer belt was damaged in about 68 hours.

As described above, the tension can be made constant regardless of the difference in the circumferential length of the conveyor belt 30, so that stable traveling of the conveyor belt 30 can be ensured and the conveyor belt 30 can be highly durable. Can be realized.

Further, since both ends of the tension roller 34 are independently held by the arm members 40, the conveying belt 3 having a circumferential length difference at both ends.
It becomes possible to apply a more uniform tension to 0.

Further, the arm member 40 at both ends of the tension roller 34 is formed of a resin component integrally molded of a resin material having good slidability, whereby the tension roller 3
Since it is possible to configure the rotating function of the bearing and the holding member of No. 4 with a small number of parts, it is possible to keep the belt tension of the conveyor belt 30 constant at a low cost.

As described above, by arranging the arm member 40 and the tension spring 35 inside the conveyor belt 30, it is possible to save space and simplify the structure, but in principle, It is also possible to dispose the arm member 40 and the tension spring 35 on the outer side of the conveyor belt 30, and in this case, the same effect can be obtained.

In the above description, the present invention has been described by exemplifying the case where the endless belt is the conveyor belt 30 for carrying the recording material P on the surface thereof, but the present invention is not limited to this. Even when the endless belt is a photosensitive belt or an intermediate transfer belt, the basic configuration can be applied almost as it is.

[0061]

As described above, according to the present invention,
An arm member for supporting the tension roller and a biasing member for bringing the tension roller into contact with the endless belt via the arm member are provided. As the circumferential length of the endless belt increases, the rotational moment of the tension roller by the biasing member is increased. By arranging so as to be large, the tension of the endless belt can be kept substantially constant with an inexpensive structure even when the circumferential length of the endless belt changes. Furthermore, this can reduce the biasing force of the endless belt in the one-sided movement and the meandering movement, so that the running stability and the durability of the endless belt can be improved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a schematic configuration of an image forming apparatus according to the present invention.

FIG. 2 is a partially cutaway perspective view near a regulation roller.

FIG. 3 is a perspective view showing a configuration of a tension applying mechanism (arm member, tension spring).

4A, 4B, and 4C are operation explanatory views showing the operation of the tension applying mechanism.

FIG. 5 is a vertical sectional view showing a schematic configuration of a conventional image forming apparatus.

6A, 6B, and 6C are operation explanatory views showing the operation of a conventional transfer roller.

[Explanation of symbols]

30 Endless belt (conveyor belt) 34 Tension roller 35 Biasing member (tensile spring) 40 Arm member 41 Swing center of arm member (rotation axis) 100 image forming apparatus 101 image forming apparatus main body Line of action of α biasing member (tensile spring)

Continued front page    F-term (reference) 2H035 CA05 CB06 CF01                 2H071 BA42 BA43 CA05 DA16                 2H072 AB07 BA03 BA12 BA17 BA20                       CA01 CA02 CA06 CB09 FA01                       JA03                 2H200 FA17 GA12 GA23 GA24 GA47                       HA02 HB12 HB22 JA02 JB07                       JB31 JB39 JB45 JB46 JC04                       JC07 JC09 JC15 JC16 LA17                       LA23 LA25 LC03 MA04 MB04                 3F049 AA10 BB07 BB12 DA04 LA01                       LB03

Claims (8)

[Claims] 1. A tension applying mechanism for applying a tension to an endless belt wound around a plurality of rollers, wherein a tension roller abutting against the endless belt and a swingable support for rotatably supporting the tension roller. An arm member; and an urging member that urges the arm member to press the tension roller against the endless belt, and a rotation moment applied to the tension roller by the urging member via the arm member. The tension applying mechanism, wherein the arm member and the urging member are arranged such that the endless belt has a larger circumferential length. 2. The angle formed by the line connecting the center of rotation of the tension roller and the center of swing of the arm member and the line of action of the urging member increases as the circumferential length of the endless belt increases. The tension applying mechanism according to claim 1, wherein the arm member and the urging member are arranged in the. 3. The tension applying mechanism according to claim 2, wherein the arm member and the urging member, which act individually, are arranged on each of both ends of the tension roller in the longitudinal direction. 4. The tension applying mechanism according to claim 1, wherein the arm member is formed of a resin component integrally molded of a resin material having good slidability. 5. An image forming apparatus comprising an image forming unit for forming an image on a recording material and an endless belt, wherein the endless belt is the endless belt according to any one of claims 1 to 4. An image forming apparatus characterized by the following. 6. The image forming apparatus according to claim 5, wherein the endless belt is a photosensitive belt on the surface of which a toner image is formed. 7. The image forming apparatus according to claim 5, wherein the endless belt is an intermediate transfer belt to which an image formed on an image carrier is transferred. 8. The image forming apparatus according to claim 5, wherein the endless belt is a conveyor belt that carries and conveys a recording material on which an image formed on an image carrier is transferred. .