JPH07178840A - Method for correction of precision of endless belt and its apparatus - Google Patents

Abstract

PURPOSE:To provide an improving method for correction of uniform surface precision and thickness precision of an endless belt and its apparatus. CONSTITUTION:An endless belt 5 having a thermoplastic resin layer on a surface layer is brought into facial contact along an outer periphery of a specular metal rotary drum by pressing. After melting a surface layer of the endless belt 5 by heating while rotating it in synchronism therewith, it is cooled. A method for correction of precision of the endless belt wherein the abovementioned process is repetitively carried out, and one set of nip rollers 7 consisting of a combination of a driving roller 2 and a driven roller 4 are provided. A specular metal rotary drum 1 is equipped to the driving roller 2. Then, the endless belt 5 having the thermoplastic resin on the surface layer is equipped to a rotary roller consisting of a plurality of rollers containing the driven roller 4. The endless belt 5 is so arranged as to come in facial contact with the rotary drum 1 by pressing. A heating means 6 is provided at a position wherein the surface of the rotary drum can be heated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an accuracy correction method for an endless belt, in which the surface and thickness of an endless belt having a thermoplastic resin layer formed on a preformed surface are corrected at the same time to improve the accuracy with high accuracy. It relates to the device.

[0002]

2. Description of the Related Art At present, for example, an electrophotographic copying machine has a means for temporarily transferring an intermediate image onto an endless belt made of a thermoplastic resin or the like before drawing a toner image formed on a photoconductor on a copy sheet. ing. The endless belt for intermediate transfer used here is important for accurately reproducing a document image with high image quality. Therefore, extremely high levels of quality and performance are required. With the recent colorization, the demand is becoming more and more sophisticated. The required characteristics are mainly the following items A to D. That is, A.
The transfer surface of the endless belt must be extremely smooth. In other words, it must be a smooth surface with no local irregularities on the surface and no lines or wrinkles in the vertical and horizontal directions. B. The endless belt itself has a constant thickness and no variation. C. The circumference of the endless belt is constant and does not expand or contract during use. D. The endless belt is in a constant (no variation) semiconducting region necessary for exhibiting good transferability, and particularly, A to C are severely required.

Conventionally, the endless belt made of a thermoplastic resin is manufactured by a molding method such as blow molding, inflation molding, inside mandrel molding, or coating method. However, the above-mentioned requirements A, B, C, D are required. In reality, none of the molding methods is sufficient to satisfy all of them. As a method for improving these conventional molding methods, there has been proposed a method in which the belt previously molded by these conventional methods is further modified by another method. For example, Japanese Patent Laid-Open No. 4-30
No. 3628, JP-A-4-303629, JP-A-4-303630, an endless belt made of a thermoplastic resin formed by a conventional method is arranged so as to face the outer circumference or the inner circumference of a steel pipe, It is described that a roller separately arranged on the outer circumference or the inner circumference of the steel pipe holds the endless belt, and heats and presses it to perform a rolling press, a surface layer of the steel pipe and the endless belt, or a cold roller or a hot roller and an endless belt. Since the contact method of the surface layer of the belt is performed by contact between the roller and the steel pipe, that is, line contact,
The finish accuracy of the surface of the endless belt was unsatisfactory.

Further, in the one disclosed in Japanese Patent Laid-Open No. 4-303631, a hot roller or the like is brought into contact with the surface of the endless belt via a heat resistant sheet, but in any case, the pressing force of the roller is sufficient. However, variations in the thickness of the endless belt and variations in surface roughness were large and insufficient. These methods are improved methods for correcting the accuracy of the surface and thickness of the belt as compared with the conventional methods, but they are not satisfied with strict quality performance requirements and need further improvement. It was

[0005]

Accordingly, the present inventors have proposed the above-mentioned A, A and B for the thermoplastic resin endless belt.
As a result of diligent studies on the development of a technology for processing with extremely high precision in response to the quality and performance requirements of B, C, and D, an improved method for correcting the surface roughness and thickness accuracy of the endless belt as compared with the above-mentioned conventional technology. And developed the device and reached the present invention.

[0006]

The present invention is achieved by providing the following means. First, as a method thereof, along the outer periphery of the mirror-finished metal rotary drum, an endless belt having a thermoplastic resin layer on the surface layer is pressed into surface contact, and the surface layer of the endless belt is heated and melted while being synchronously rotated, and then cooled. This step is repeated.

Then, the following apparatus is provided to achieve the above method. That is, a pair of nip rollers composed of a combination of a main rotation roller and a sub rotation roller is provided, a mirror-finished metal rotary drum is mounted between the nip rollers, and a plurality of rotation rollers including the sub rotation roller are heated to the surface layer. An endless belt having a plastic resin layer is mounted, and the endless belt is arranged to make surface contact with the rotary drum by pressing, and a heating means is provided at a position where the surface of the rotary drum can be heated. The main rotation roller and the at least one auxiliary roller are mounted, and the main rotation roller is supported by at least two support rollers.

In the present invention, the heating for heating and melting means heating at least above the softening point temperature of the thermoplastic resin layer, preferably above the melting point. The thermoplastic resin layer is a resin layer that is softened or melted by heating and can be molded, and is generally known. For example, polypropylene, polystyrene, A
General-purpose resins such as BS resins, various aliphatic polyamides, or alcohol-soluble polyamides obtained by N-methoxymethylating these polyamides, various polyesters, polycarbonates, polyether sulfones, fluororesins, polyether ether ketones, thermoplastics It is a layer made of a functional resin such as polyimide, polyamideimide, polyether nitrile, or polyurethane, and may be a mixture of two or more of these as appropriate. These resins are examples, and the present invention is not limited thereto.

An endless belt having a thermoplastic resin layer as a surface layer is an endless cylindrical member formed by a molding method of the above-mentioned thermoplastic resin or a mixed resin thereof, which is generally known, Alternatively, it may be a composite belt in which other components are combined. For example, a composite between the thermoplastic resins, or a thermosetting resin, for example, a film-like or cloth-like endless belt made of aromatic polyimide, aromatic polyamide or the like, or a composite cloth-like of these and an aliphatic polyamide An endless belt or the like may be used as a base belt, and the surface thereof may be melt-coated with the thermoplastic resin, or a belt obtained by applying the thermoplastic resin in a melted state to form a composite is also applicable. The thickness of the surface layer is preferably at least a thickness necessary for the surface of the endless belt to be smooth, and at most ½ or less of the belt thickness.

When the thermoplastic resin is formed into an endless cylinder, it is possible to mix other components and form the mixture. By mixing a powdery conductive material, a semiconductive endless belt is obtained. be able to. Examples of the conductive substance include carbon black, stannic oxide, indium oxide, potassium titanate, black titanate, whisker titanate, and the like, and two or more kinds thereof may be mixed. Here, carbon black is obtained by appropriately burning natural gas, oil, acetylene gas, etc., and has a particle size of about 5
It has a thickness of up to 500 μm and is called by the names such as Ketchin black and acetylene black. The mixing amount of these is
The amount required to obtain the required semiconductivity is determined on the assumption that the original mechanical properties are not deteriorated, and preferably about 5 to 20% (weight) with respect to the thermoplastic resin.

Further, as other components for further improving the compatibility or moldability of the resin, for example, wax, silicone oil, low molecular weight oligomers of various resins, etc. can be mixed. Even in these cases, the mixing amount is a few% of the resin.
A small amount of (weight) or less is preferable. Further, in order to improve the creep resistance and the like of the endless belt, an inorganic filler such as talc and mica, a liquid crystal polymer, and an organic filler such as aramid fiber may be added. The mixing amount of these is about 5 to 20% (weight) with respect to the thermoplastic resin. The addition of other components, including the above examples, is performed as necessary and may not be mixed.

Next, the method of the present invention will be described in detail together with one embodiment of the apparatus. FIG. 1 is a side view showing an entire embodiment of the method of the present invention, and FIG. 2 is a side view of an embodiment of the apparatus of the present invention.

The mirror-finished metal rotary drum 1 is a thin-walled metal drum whose outer peripheral surface is mirror-finished, and the preferable thickness is 1.
It is preferable that the surface roughness Rz (10-point average roughness) is about 2 μm or less. The outer diameter of the drum 1 is sufficiently large, that is, when the endless belt 5 mounted on a plurality of rotating rollers 3 and 4 described later comes into surface contact with the drum 1 by pressing, the circumference of the drum 1 is reduced. It is preferable that the amount is less than half. The dimension of the drum 1 in the width direction is preferably at least the width of the endless belt 5.

The mirror finishing accuracy of the rotary drum 1 directly affects the surface roughness of the endless belt 5 and is an important factor. Further, the wall thickness of the drum 1 is preferably as thin as possible in view of the heating / cooling cycle, but if the thickness is 1 mm or less, the difficulty in terms of manufacturing technology doubles, and if it is 5 mm or more,
It is not preferable because the heating and cooling cycle takes a long time.

As shown in FIG. 3, the rotary drum 1 may be a direct rotary system in which a cylindrical rotary roller having rotary shafts 1a at both ends of the central shaft is used, but as shown in FIG. 1 is a cylindrical tubular body only, and is mounted on the main rotating roller 2 and at least one auxiliary roller 2a disposed inside thereof, and is synchronized by the pressing force and rotation of the nip roller 7 composed of the main rotating roller 2 and the subsidiary rotating roller 4. The indirect rotation method of being rotated is preferable. This is because the indirect rotation method has an advantage that distortion does not occur even if the thickness of the rotary drum 1 is thin and the apparatus is compact. Here, a heating unit and / or a cooling unit for preliminarily heating the drum 1 may be additionally provided inside the rotary drum 1.

As described above, the nip roller 7 is composed of one set of the main rotating roller 2 and the sub rotating roller 4, and the sub rotating roller 4 is provided so as to be able to press the main rotating roller 2 and to have an endless belt. It is equipped with a detachable mechanism that can be installed in 5 rolls. The rotary drum 1 is mounted on the main rotary roller 2, the endless belt 5 is mounted on the slave rotary roller 4, and the nip roller 7 presses and nips the main rotary roller 2 to rotate, so that the rotary drum 1 and the endless belt 5 , The slave rotation roller 4 rotates together.

Since the endless bell 15 is wound around the rotary roller 3 and the like including a plurality of sub-rotating rollers 4, and the rotary roller 3 is arranged so as to come into contact with and separate from the rotary drum 1, the endless bell 15 is arranged. The belt 5 is pressed and brought into contact with the surface of the rotary drum 1 between the sub-rotation roller 4 and the rotation roller 3 to rotate synchronously while making surface contact, and is detached after the operation is completed.

At this time, the distance between the sub-rotating roller 4 and the rotating roller 3 may be fixed, but a mechanism that can be adjusted may be provided if necessary. Further, in relation to the circumference of the endless belt 5, the rotation roller 3a may be provided so that its position can be adjusted as shown in FIG. 4 if necessary, and the tension of the endless belt 5 can be adjusted, as shown in FIG. So that the endless belt 5
And the rotary roller 3 at a position that assists the pressing of the rotary drum 1 with the rotary drum 1.
b or the like may be provided. At least the rotating rollers 3, 3b and the like that press against the rotating drum 1 are detachable from the surface of the drum 1, and the endless belt 5 can be attached and detached in a wound manner. The distance between the sub-rotating roller 4 and the rotating roller 3 is preferably shorter than the peripheral length of the rotary drum 1 and at most half the peripheral length of the rotary drum 1. However, this distance is determined by the physical properties of the resin belt constituting the surface layer of the endless belt 5, such as the softening point, the melting point, the crystallinity, and the thickness. The resin layer softened or melted by heating is the rotating drum. A sufficient distance is required to make pressure contact with the surface of No. 1 and be molded.

The sub-rotating roller 4, the rotating roller 3 and the like are preferably metal rollers having smooth surfaces, but may be made of plastic. The diameter of the sub-rotating roller 4 is preferably equal to or less than the diameter of the main rotating roller 2. The width dimensions of the rotary roller 3 and the sub-rotary roller 4 are
It is preferably equal to the width of the rotary drum 1. It is preferable that the surfaces of the rotating roller 3 and the sub-rotating roller 4 are smooth, but when the endless belt 5 is wound and mounted, it is not preferable that slip occurs between the rotating rollers 3 and 4 and the endless belt 5. Therefore, it is possible to coat the surfaces of the rotating rollers 3 and 4 with silicone rubber or the like to make them non-slip.

The diameter of the main rotary roller 2 described above is at least smaller than the inner diameter of the rotary drum 1, and preferably can be arranged inside the rotary drum 1 together with the two auxiliary rollers 2a and 2b as in the embodiment. Dimensions are preferred. The roller 2 is made of a metal roller having a smooth surface, and has a structure that can cope with the pressing nip force (about 1000 kg) of the slave rotation roller 4.

The auxiliary rollers 2a and 2b are sufficient as long as they have a structure for supporting the rotary drum 1, and may be simple guide rollers. The supporting rollers 2c and 2d support the main rotating roller 2 and reinforce the same, so that the diameter of the supporting roller 2c is reduced.
It is possible to reduce the diameter of the.

The heating device 6 is not particularly limited, but any device that heats the mirror surface metal rotary drum 1 in order to indirectly heat and soften or melt the surface layer of the endless belt 5 is applicable. Is. For example, far infrared rays or the like may be used directly, but a type in which the air is heated using a heat source such as far infrared rays, nichrome wire, or ceramics, and the hot air is discharged from a slit-shaped nozzle is preferable. The arrangement of the heating device 6 is not particularly limited as long as it can heat the surface of the mirror-like metal rotary drum 1, but in the embodiment, it is provided in front of the nip roll 7. The heating temperature is appropriately changed depending on the melting point or softening point of the processed resin of the endless belt 5.
At the time of heating, it is important not to melt or soften the entire endless belt, but it is important to melt or soften only the surface layer of the endless belt, so it is necessary to appropriately change the heating conditions depending on the type of the thermoplastic resin. is there.

Further, although not shown in the drawing, a cooling device or a water pipe for cooling may be provided inside the rotary drum 1, the main rotary roller 2, the sub rotary roller 4, etc.,
Even if there is no cooling device in particular, room temperature or natural cooling is possible.

An accuracy correction method for an endless belt using the above apparatus will be described. As shown in FIG. 1, the endless belt 5 is wound around and attached to the secondary rotation roller 4 and the rotation roller 3,
The sub-rotating roller 4 presses against the main rotating roller 2 via the mirror-finished metal rotating drum 1, and the rotating roller 3 rotates.
Since it comes into pressure contact with, the thermoplastic resin layer of the surface layer of the belt 5 makes surface contact with the surface of the rotary drum 1.

Next, since the main rotary roller 2 is driven and rotated, the mirror-finished metal rotary drum 1, the slave rotary roller 4, and the endless belt 5 are synchronously rotated, and the heating device 6 is operated.
The surface layer of the endless belt 5 is heated to be in a softened or molten state. At this time, since the nip roll 7 is strongly nipped, the thickness of the endless belt 5 is regulated to the minimum value, and the surface of the endless belt 5 is pressed into contact with the surface of the mirror-finished metal rotary drum 1 and cooled while being synchronously rotated. After being removed, since it is peeled off from the drum, variations in the surface roughness of the belt 5 are improved.

After the lapse of a predetermined time, the heating device 6 is stopped, and after cooling appropriately, the endless belt 5 may be detached. At this time, it is preferable to rotate the endless belt 5 even during cooling.
Here, the predetermined time may be determined experimentally, and the thickness and surface roughness of the endless belt 5 are sufficiently corrected,
Time to settle, often achieved within about 60 minutes, but not limited to this.

Cooling is the temperature at which the thermoplastic resin layer of the surface layer solidifies, and is cooled to a temperature below the softening point or melting point of the resin. After the cooling is completed, the pressing nip or pressing contact of the sub-rotating roller 4, the rotating roller 3 and the like may be opened and the endless belt 5 may be detached.

[0028]

The surface layer made of the thermoplastic resin layer of the endless belt is pressed against the outer surface of the mirror-finished metal rotary drum 1, and the surface layer is heated while being in surface contact to be softened or melted, and the surface layer is cooled and solidified. After peeling off from the drum,
Since the surface roughness of the endless belt is corrected and the nip roller regulates the surface to a minimum size, variations in the thickness of the endless belt are reduced and stabilized.

[0029]

EXAMPLES The present invention will be described in detail with reference to Examples and Comparative Examples. (Example 1) N-methoxy was formed on the outer surface of an endless cylindrical knitted fabric having a width of 400 mm and a peripheral length of 603 mm knitted with a milling change knitting structure of nylon 6 fiber yarn and aramid fiber yarn (aromatic polyamide, manufactured by DuPont). Methylated polyamide 6 was dissolved in methyl alcohol at a concentration of 80% (by weight), 7% (by weight) (to polyamide 6) of Ketchin black was added thereto, and uniformly mixed by using a ball mill. The liquid is uniformly coated. After coating, it is dried at 60 ° C. for 3 hours to manufacture an endless belt. This product had a width of 400 mm, a peripheral length of 603 mm, a thickness of 0.3 mm ± 0.025 mm, and a surface roughness Rz of 20 microns. This is hereinafter referred to as an A belt. The surface roughness Rz is a ten-point average roughness.

On the other hand, an endless belt precision correction device B shown in FIG. 1 is prepared. That is, using a mirror-finished metal rotary drum 1 having a surface roughness Rz of 1.0 micron or less, a width of 500 mm, a perimeter of 900 mm and a thickness of 3.0 mm, a metal having a diameter of 75 mm and a width of 500 mm was used as the main rotary roller 2 on the inner surface thereof. Arrange the rollers. In addition, the auxiliary roller 2 is used as a sub roller.
a, 2b and supporting rollers 2c, 2d to the state shown in FIG.
Book arrangement. A rotary roller 3 for mounting the endless belt 5 and a sub-rotary roller 4 are arranged along the outer periphery of the mirror-finished metal rotary drum 1 as shown in FIG. 1. These two rollers 3 and 4 are air cylinders. The mechanism makes it detachable. The sub-rotating roller 4 has a diameter of 75 mm and a width of 500 m.
The rotating roller 3 has a diameter of 35 mm and a width of 500 mm. The distance between the rotating roller 3 and the sub-rotating roller 4 is
It has a mechanism of adjustable length that can be freely changed.
Further, the sub-rotating roller 4 is provided with a mechanism capable of cooling the cooling medium such as cold water so as to pass through the roller. Heating device 6
Consists of a hot air generator capable of heating up to 350 ° C. (± 2 ° C.) and has a slit-shaped outlet with a width of 500 mm.

Next, a device B for correcting the accuracy of the endless belt 5
A detailed description will be given of a method for uniformly processing the surface roughness and the thickness.

First, the rotary roller 3 and the slave rotary roller 4 of the apparatus B are separated from the mirror-finished metal rotary drum 1, and the endless belt 5 is moved.
Put on. The endless belt 5 is attached to the sub-rotating roller 4, and the pressure is applied along the outer periphery of the rotating drum 1 by using the air cylinder as the rotating roller 3. And nip roll 7
The rotating roller 3 is pressed so that the contact pressure becomes 1000 kg with a width of 400 mm.

Then, the mirror metal rotating drum 1, the rotating roller 3, the slave rotating roller 4, and the endless belt 5 are synchronously started at a speed of 100 mm per minute, and then the surface of the rotating drum 1 is heated to 160 ° C. for 5 minutes. The hot air is supplied at a temperature rising rate, and rotation is continued for 25 minutes at this temperature. After 25 minutes have passed, the hot air supply is stopped and the temperature is cooled to 70 ° C. The work of taking out the endless belt 5 as the straightening belt is completed. The quality characteristics of the belt straightened as described above have a surface roughness Rz1.5.
Micron or less (entire surface), thickness accuracy 0.27 mm ± 0.0
The length was 10 mm, which was a significant improvement over the unprocessed endless belt A, and the characteristics required by the user were sufficiently cleared.

(Example 2) Polyvinylidene fluoride was extruded into a tubular shape and molded to give a width of 400 mm and a peripheral length of 628 m.
m, thickness 0.2 mm ± 0.015 mm, surface roughness Rz2
A micron (all surface) belt C was molded. The belt C was attached to the device B, and the same operation as in Example 1 was carried out to carry out straightening. However, in the heating method, a rod-shaped ceramic heater for preheating was attached to the slit exit of the heating device 6 and heated to 175 ° C. After straightening for 25 minutes, the belt was cooled to 70 ° C. and taken out. The quality of the belt after straightening is 0.18 mm ± 0.006 mm,
Surface roughness Rz is less than 1.5 microns (all surfaces),
It was a great improvement over the raw belt C.

Example 3 An aromatic polyamic acid solution was centrifugally molded, dried by heating, taken out, and further heated at 350 ° C. to cause a ring-closing reaction to mold a thermosetting polyimide tube. The polyurethane resin solution is surface-coated on one side of the tube. For the coating, a polyimide tube was rotated in the circumferential direction, and the entire surface was uniformly applied by spray coating.

The quality of the obtained two-layer endless belt D was 400 mm in width, 610 mm in perimeter, surface roughness Rz of 3 microns, and thickness of 0.12 mm ± 0.020 mm. Next, this belt D is similarly mounted on the rotating roller 3 and the sub-rotating roller 4 in the device B, and heated and straightened. However, the heating temperature in this case was 150 ° C. After straightening for 25 minutes, it was cooled to 70 ° C. to obtain a straightened belt for taking out. The quality of this processing belt is 0.11mm thick
The surface roughness was ± 0.008 mm and the surface roughness Rz was 1.5 μm or less (all surfaces), showing a significant improvement over the belt D before straightening.

(Comparative Example) In the device B, the position of the rotary roller 3 is arranged above the position of the sub-rotation roller 4, and only the sub-rotation roller 4 is pressed into contact with the mirror-finished metal rotary drum 1. . This device is referred to as device E, and FIG.
Shown in. The rotating roller 3 whose position has been changed is displayed as 3C. Next, the endless belt A produced in the same manner as in Example 1 is mounted on the apparatus E, and only the sub-rotating roller 4, that is,
Only the nip roll 7 was pressed and nip-rotated synchronously at a speed of 100 mm / min. At this time, the nip roll 7 has 1000
A nip force of kg / 400 mm was applied. Next, the surface of the mirror-like metal rotary drum 1 was heated for 5 minutes, kept at 160 ° C. and kept rotating for 25 minutes, and then the heating was stopped, the temperature was cooled to 70 ° C. and the rotation was stopped. Belt A was taken out.

The quality of this belt has a thickness of 0.026 mm.
The surface roughness was ± 0.065 mm and the surface roughness Rz was 5 to 25 μm. In this comparative example, the linear contact method of the mirror-finished metal rotary drum and the endless belt was adopted as a typical example of the prior art, and the straightening process was tried, but the difference in the effect is obvious as compared with the present invention. Understand that

[0039]

According to the method of the present invention, the accuracy of the endless belt having the thermoplastic resin layer as the surface layer, that is, the thickness and variation of the belt and the surface roughness of the belt can be corrected with high accuracy. Further, in the device of the present invention, it is possible to provide an efficient straightening device having a short heating and cooling cycle and a device having a simple structure.

[Brief description of drawings]

FIG. 1 is a side view showing the entire method of the present invention.

FIG. 2 is a side view showing an embodiment of the device of the present invention.

FIG. 3 is a perspective view showing another embodiment of a mirror surface metal rotary drum.

FIG. 4 is a side view showing an embodiment provided with a rotating roller 3a.

FIG. 5 is a side view showing an embodiment in which a rotary roller 3b is provided.

FIG. 6 is a side view showing a conventional accuracy correction device for an endless belt.

[Explanation of symbols]

 1 Mirror-like metal rotating drum 2 Main rotating roller 2a Auxiliary roller 2b Auxiliary roller 2c Supporting roller 2d Supporting roller 3 Rotating roller 4 Secondary rotating roller 5 Endless belt 6 Heating device 7 Nip roller

Claims (4)

[Claims] 1. An endless belt having a thermoplastic resin layer on its surface layer is pressed into surface contact with the outer periphery of a mirror-finished metal rotary drum, and the surface layer of the endless belt is heated and melted while being synchronously rotated, and then cooled. An endless belt accuracy correction method characterized by repeating steps. 2. A pair of nip rollers consisting of a combination of a main rotating roller and a sub rotating roller, a mirror surface metal rotary drum is mounted between the nip rollers, and a surface of the rotary roller composed of a plurality of sub rollers including the sub rotating roller. An endless belt having a thermoplastic resin layer as a layer is mounted, the endless belt is arranged to come into surface contact with the rotary drum by pressing, and a heating means is provided at a position capable of heating the surface of the rotary drum. Endless belt accuracy correction device. 3. The endless belt precision correcting device according to claim 2, wherein the mirror-finished metal rotary drum is mounted on the main rotary roller and at least one auxiliary roller. 4. The accuracy correcting device for an endless belt according to claim 2, wherein the main rotating roller is supported by at least two supporting rollers.