JP4438992B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus including a belt unit such as a conveyance belt and an intermediate transfer belt, and more particularly to positioning of a belt unit.

JP 2001-324858 A JP 2000-235309 A

  In recent years, there has been a rapid increase in demand for full-color image forming apparatuses, improved printing speeds, and smaller apparatuses. In order to satisfy this demand, so-called quadruple tandem image forming apparatuses are increasing. In the quadruple tandem system, four image forming units including an image carrier and a developing device are arranged facing a belt unit such as a transfer belt (transfer belt) or an intermediate transfer belt, and a toner image on each image carrier is arranged. It is directly transferred onto a sheet or transferred onto an intermediate transfer belt and then transferred onto the sheet at once, and is characterized in that a full color image can be obtained in a short time.

In order to position the belt unit in the image forming apparatus of this type, conventionally, a main reference is often provided on a driving roller for driving the belt.
For example, Japanese Patent Laid-Open No. 2001-324858 (Patent Document 1) describes positioning a cleaning member and a support plate with reference to a drive shaft of an intermediate transfer unit (paragraph [0039]).

  Japanese Patent Laid-Open No. 2000-235309 (Patent Document 2) discloses that when the belt unit is mounted on the apparatus main body by the first and second guide rollers disposed on the same axis as the central axis of the belt driving roller. First, positioning is described (paragraph [0025], FIG. 2).

  However, even if the drive roller shaft is set as the main reference in the belt unit, the position of the sub-reference is not specified, and it is often determined simply by the convenience of the layout. In such a configuration, there is a problem in that the belt misalignment deteriorates depending on the tolerance variation of the reference standard, and in the worst case, the belt is detached from the normal position of the roller and the belt is damaged. .

  As countermeasures, conventionally, the precision of parts and assembly are strictly controlled, and the position of the roller is adjusted to prevent the belt from being detached or damaged. However, there is a problem that strict management of component accuracy and assembly accuracy leads to an increase in cost.

  The present invention solves the above-described problems in an image forming apparatus including a belt unit such as a conveyance belt and an intermediate transfer belt, and can easily perform positioning of the belt unit at low cost, and image formation that hardly causes belt misalignment. It is an object to provide an apparatus.

According to the present invention, there is provided a belt unit in which an endless belt is stretched on at least two support rollers including a driving roller and a tension roller, and positioning of the belt unit with respect to a main body device is performed on the shaft of the driving roller. In the image forming apparatus, the drive roller and the tension roller are set as two rollers having the longest distance in the belt circumferential direction among the support rollers on which the belt is stretched, and the belt unit is positioned with respect to the main body device. as sub-reference, solved by a sub-reference axis that passes through between both side plates for supporting the driving roller and a tension roller, wherein the support rollers within the belt loop between the drive roller and the tension roller is provided disposed separately Is done.

In order to solve the above problems, the present invention proposes that the tension roller is provided so as to be movable substantially parallel to the ideal position of the slave reference shaft.
In order to solve the above-described problem, the present invention is directed to a direction in which the tension roller can be moved in a direction that is approximately a half of a winding angle of the belt on the tension roller, and a tension direction with respect to the belt. We propose that it is almost the same.

  In order to solve the above problems, the present invention proposes that the sub-reference shaft is arranged on or near a line connecting the shaft of the drive roller and the shaft of the tension roller.

Moreover, in order to solve the said subject, this invention proposes that the base material of the said belt is a polyimide resin.
In order to solve the above problems, the present invention proposes that the belt unit is a transfer conveyance belt that transfers an image from an image carrier while holding and conveying a recording medium.

  In order to solve the above-described problems, the present invention proposes that the belt unit is an intermediate transfer belt that transfers an image onto an image recording medium after the image is transferred and held from an image carrier.

According to the image forming apparatus of the present invention, the drive roller and the tension roller are set as the two rollers having the longest distance in the belt circumferential direction among the support rollers on which the belt of the belt unit is stretched, and the main body device of the belt unit As a secondary reference for positioning with respect to the belt roller, a secondary reference shaft that penetrates between both side plates that support the drive roller and the tension roller is provided separately from the support roller in the belt loop between the drive roller and the tension roller. Is corrected so as to maintain the parallelism of the tension roller. Therefore, the belt is prevented from being displaced and the belt is prevented from being damaged. Further, the belt unit can be easily positioned by the slave reference shaft that passes between both side plates of the unit provided separately from the support roller .

  According to the second aspect of the present invention, since the tension roller is provided so as to be movable substantially parallel to the ideal position of the slave reference shaft, the correction action due to the deviation of the belt tension is efficiently performed.

  According to the configuration of the third aspect, since the direction in which the tension roller can be moved is approximately ½ of the belt winding angle and substantially the same as the tension direction with respect to the belt, the resistance when correction is made is reduced. Further reduction and more efficient correction are performed.

  According to the configuration of the fourth aspect, since the secondary reference shaft is arranged on or near the line connecting the shaft of the drive roller and the tension roller, twisting of the tension roller from the influence of the parallelism with respect to the primary reference of the secondary reference is minimized. Thus, the belt offset force can be reduced.

  With the configuration of claim 5, since the base material of the belt is a polyimide resin, even when correction is performed so as to maintain the parallelism of the tension roller, the expansion / contraction of the belt is suppressed, and therefore correction of the belt shift is more efficient. Therefore, the occurrence of belt deviation is reliably suppressed.

  According to the configuration of the sixth aspect, the belt of the transfer conveyance belt that transfers the image from the image carrier while holding and conveying the recording medium is prevented. Further, the image quality can be maintained.

  According to the seventh aspect of the present invention, it is possible to prevent the intermediate transfer belt from being displaced from the intermediate transfer belt which is transferred onto the recording medium after the image is transferred and held from the image carrier. Further, the image quality can be maintained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a schematic configuration of a full-color printer which is an example of an image forming apparatus according to the present invention. The color printer shown in this figure has four image forming units (image stations) (image stations) arranged substantially in the center of the main body. The belt unit 10 is disposed on the upper side of the four image forming units, and the optical writing device 8 is disposed on the lower side.

  Each image forming unit has photoreceptor drums 20Y, 20C, 20M, and 20Bk as image carriers, and around them, dedicated chargers 30Y, 30C, 30M, and 30Bk, and developing devices 50Y, 50C, 50M, and 50Bk. Primary transfer rollers 12Y, 12C, 12M, and 12Bk, cleaning devices 40Y, 40C, 40M, and 40Bk are provided.

One of these image forming units is shown enlarged in FIG. In FIG. 2, the symbols Y, C, M, and Bk representing the color image forming units are omitted.
As shown in FIG. 2, the developing device 50 includes a developing case 55 having an opening, a developing roller 51 disposed so as to face the surface of the photosensitive drum 20, and the developer on the developing roller 51 at a certain height. It is composed of a developing blade 52 to be regulated, a first conveying screw 53 and a second conveying screw 54 arranged at positions facing the developing roller 51.

  The cleaning device 40 includes a cleaning case 43 having an opening, a cleaning blade 41 for cleaning residual toner on the photosensitive drum 20, a waste toner screw 42 for transporting the cleaned waste toner to a waste toner bottle (not shown), and the like. It is comprised by.

  The belt unit 10 includes an intermediate transfer belt 11, a primary transfer roller 12 for transferring the toner image on the photosensitive drum 20 to the intermediate transfer belt 11, an intermediate transfer belt case 13 for holding these components, and the like. Has been. Reference numeral 30 denotes a charging roller as a charging device, 31 denotes a cleaning roller for the charging roller, and L denotes laser light from the optical writing device 8.

  Returning to FIG. 1, reference numeral 9 shown at the upper left of the apparatus main body indicates a toner bottle for replenishing toner. From the left, yellow (Y), cyan (C), magenta (M), black (Bk The toner is supplied to the developing devices 50Y, 50C, 50M, and 50Bk of the color image forming units by a predetermined supply amount through a conveyance path (not shown).

  The color image forming operation is detected by a sensor (not shown) when the transfer paper 2 is fed from the paper feed cassette 1 disposed at the lower part of the apparatus body by the paper feed roller 3 and the leading edge of the transfer paper 2 reaches the registration roller pair 4. Then, the transfer sheet 2 is conveyed to the nip portion between the secondary transfer roller 5 and the intermediate transfer belt 11 by the registration roller pair 4 while taking a timing with this detection signal.

  On the other hand, in each color image forming unit, the photosensitive drums 20Y, 20C, 20M, and 20Bk, which are uniformly charged in advance by the charging devices 30Y, 30C, 30M, and 30Bk, are exposed and scanned by the optical writing device 8 with laser light. Then, electrostatic latent images are formed on the photosensitive drums 20Y, 20C, 20M, and 20Bk. The electrostatic latent images are developed by the developing devices 50Y, 50C, 50M, and 50Bk for the respective colors, and yellow, cyan, magenta, and black toner images are formed on the surfaces of the photosensitive drums 20Y, 20C, 20M, and 20Bk. .

  Next, a voltage is applied to the primary transfer rollers 12Y, 12C, 12M, and 12Bk, and the toner on the photosensitive drums 20Y, 20C, 20M, and 20Bk is sequentially transferred onto the intermediate transfer belt 11. At this time, the image forming operation for each color is executed while shifting the timing from the upstream side to the downstream side so that the toner image is transferred to the same position on the intermediate transfer belt 11. The image formed on the intermediate transfer belt 11 is conveyed to the position of the secondary transfer roller 5 and is secondarily transferred to the transfer paper 2. The transfer paper 2 onto which the toner images of the respective colors are transferred is conveyed to the fixing device 6 and thermally fixed, and is discharged by the paper discharge roller 7.

  The toner remaining on the photosensitive drums 20Y, 20C, 20M, and 20Bk is cleaned by the respective cleaning devices 40Y, 40C, 40M, and 40Bk, and then the charging devices 30Y and 30C in which the bias of the AC component is superimposed and applied to the direct current. , 30M, 30Bk and charged simultaneously with static elimination to prepare for the next image formation. The residual toner on the intermediate transfer belt 11 is cleaned by the intermediate transfer belt cleaning device 19 and prepared for the next image forming process.

  FIG. 3 is an external perspective view of the belt unit 10. FIG. 4 is a perspective view showing the intermediate transfer belt 11 in a hidden state so that the internal configuration of the belt unit can be understood. As shown in these drawings, the drive roller 21, the tension roller 23 and the pre-transfer roller 16 around which the intermediate transfer belt 11 is stretched are supported by two side plates 14 and 15. Bearings 17 and 18 are press-fitted into the shaft ends of both sides of the drive roller 21, and the bearings 17 and 18 are fitted into positioning holes 60 and 61 (FIG. 9) provided in the apparatus main body to thereby The position is determined. By determining the position of the driving roller 21, the driving roller 21 (the shaft thereof) becomes a main reference in positioning the belt unit 10.

  Further, as shown in FIG. 4, a shaft (secondary reference shaft) 22 serving as a secondary reference in positioning the belt unit 10 is provided through the side plates 14 and 15. The secondary reference shaft 22 is fitted into reference holes 62 and 63 (FIG. 9) provided in the apparatus main body to determine the posture of the belt unit. Each transfer roller 12 (FIG. 1) as a primary transfer unit is also supported by the side plates 14 and 15.

  FIG. 5 is a perspective view showing the tension roller 23. As shown in this figure, support plates 24 and 24 are attached to both end portions of the tension roller 23 via bearings (not shown), and the tension roller 23 is rotatable with respect to the support plate 24. . As shown in FIG. 6 in an enlarged manner, the support plate 24 is provided with a sliding protrusion 26. A spring receiving portion is provided on a side surface of the sliding projection 26, and a pressure spring 25 is set there. The pressure spring 25 is set on the receiving portion so as to have a substantially vertical positional relationship with the axis of the roller 23. The same applies to the support plate 24 on the other end not shown in FIG.

  Further, as shown in FIG. 7, sliding holes 27 are formed in the side plates 14 and 15 that support the tension roller 23. In FIG. 7, only the side plate 14 on one side is shown, but the same applies to the side plate 15 on the other side.

  Then, as shown in FIG. 8, the tension roller 23 is rotated to the side plate 14 (15) by fitting the sliding protrusion 26 of the support plate 24 of the tension roller 23 into the sliding hole 27 of the side plate 14 (15). Supported as possible. The sliding protrusion 26 and the sliding hole 27 are loosely fitted, and the sliding protrusion 26, that is, the tension roller 23 is configured to be movable with respect to the side plates 14 and 15 as shown by thick arrows in FIG. Yes. The sliding hole 27 has a long shape in the longitudinal direction of the side plate as can be seen from FIG. When the sliding protrusion 26 is fitted into the sliding hole 27, the aforementioned pressure springs 25, 25 are set with respect to the side plates 14, 15, and the pressure springs 25, 25 serve as the tension roller 23 and the drive roller. The pressure is applied in a direction away from 21 to apply tension to the intermediate transfer belt 11.

  FIG. 9 is a schematic diagram schematically showing how the belt unit 10 is set and positioned in the printer main body of FIG. As described above, the main reference is determined by fitting the bearings 17 and 18 provided at both axial ends of the drive roller 21 into the positioning holes 60 and 61 on the apparatus main body side. Further, the slave reference is determined by fitting the slave reference shaft 22 into the reference holes 62 and 63 on the apparatus main body side.

  By the way, when the parallelism with respect to the drive roller 21 which is the main reference of the secondary reference shaft 22 is shifted, the side plates (14, 15) themselves are twisted. If the tension roller 23 is fixed to the side plates 14 and 15, the parallelism of the tension roller 23 itself with respect to the drive roller 21 is also shifted as shown in FIG. If this happens, the belt offset force (force toward the roller axis) increases, which may lead to damage to the belt.

  On the other hand, in the present embodiment, the driving roller 21 and the tension roller 23 are provided as the rollers having the longest distance between the front and rear rollers in the circumferential direction of the intermediate transfer belt 11. In this example, if the distance between the driving roller 21 and the tension roller 23 is L1, the distance between the tension roller 23 and the pre-transfer roller 16 is L2, and the distance between the pre-transfer roller 16 and the driving roller 21 is L3, in this example, L1> L2 > L3. With this configuration, even when the slave reference shaft 22 is misaligned, the tension roller 23 has a deviation in belt tension at both ends of the roller due to the balance with the circumference of the belt 11 as shown in FIG. (Explaining in FIG. 10, the belt tension at the lower end of the roller 23 is larger than the belt tension at the upper end), so that the parallelism of the tension roller 23 is maintained.

  This correction action works not only when the belt unit is viewed from above (in a plan view) as shown in FIG. 11, but also when viewed from the direction A shown in FIG. This will be described with reference to FIGS.

  13 is a front view of the rollers of the belt unit 10 as viewed from the direction A in FIG. In this figure, the secondary reference shaft 22 is not displaced, and the tension roller 23 and the parallelism with respect to the drive roller 21 are maintained.

  As shown in FIG. 14, when the slave reference shaft 22 is displaced, the parallelism of the tension roller 23 itself with respect to the drive roller 21 is also displaced. However, in the case of this figure, since the belt tension at the right end of the tension roller 23 is larger than the belt tension at the left end, a force that pushes down the right end of the roller 23 acts, and as shown in FIG. Correction is performed so that the parallelism of the roller 23 is maintained.

  In the design, the positional relationship between the secondary reference shaft 22 and the tension roller 23 is pursued from the position from the main reference (in this example, the drive roller 21), and the influence of the secondary reference shaft 22 on the tension roller 23 (tension roller). 23 torsion with respect to the main reference) is proportional to the sum of the distances from the respective main reference. This is because each processing dimension has a shorter distance and it is easier to maintain the dimensional accuracy. According to the present invention, the slave reference shaft 22 is passed through the belt loop of the transfer belt 11 (through the side plates 14 and 15), and By providing the secondary reference shaft 22 between the drive roller 21 and the tension roller 23, the total sum of the distances can be minimized and the twist of the tension roller 23 from the influence of the parallelism with respect to the primary reference of the secondary reference can be minimized. It is possible to reduce the shifting force of the belt. For this reason, in the present embodiment, the positioning accuracy of the belt unit 10 is improved, and the parallelism of the rollers around which the intermediate transfer belt 11 is stretched is increased to reduce the belt offset force, thereby breaking the belt. Etc. are also prevented in advance.

  In particular, as can be seen from FIG. 12, by arranging the secondary reference shaft 22 on or in the vicinity of the line connecting the axis of the drive roller 21 and the axis of the tension roller 23, it is possible to prevent the influence of the parallel reference to the primary reference. It is possible to minimize the twisting of the tension roller 23 and reduce the belt shifting force.

  Further, as described above, the tension roller 23 is configured to be movable (displaceable) with respect to the side plates 14 and 15 of the belt unit. The moving direction is set substantially parallel to the ideal position of the secondary reference shaft 22 (substantially parallel to the plane including the secondary reference shaft 22 and the drive roller 21 in the ideal state). Further, the longitudinal direction of the sliding hole 27, that is, the moving direction of the tension roller 23, is a direction having an angle approximately ½ of the wrapping angle of the belt 11 around the tension roller 23 (the substantially central portion of the belt wrapping range on the roller peripheral surface). And the direction in which the tension roller 23 is pressed. As a result, the correction action due to the deviation of the belt tension described with reference to FIGS. 9 to 15 can be easily performed, and the occurrence of belt misalignment can be suppressed.

  That is, by setting the moving direction of the tension roller 23 to be substantially parallel to the ideal position of the secondary reference shaft 22, the resistance when the tension roller 23 is corrected (the sliding projection 26 and the side plates 14 and 15 are not affected). (Sliding load) is reduced, and efficient correction is performed.

  In addition, since the moving direction of the tension roller 23 is a direction that is approximately ½ of the winding angle of the belt 11 around the tension roller 23, the direction in which the correction force due to the belt tension acts and the moving direction of the tension roller 23 are different. Since they substantially coincide with each other, the resistance when correction is performed is further reduced, and more efficient correction is performed.

Next, the intermediate transfer belt 11 will be described.
As an intermediate transfer belt or a conveyance belt (transfer belt) used in this embodiment, it is desirable that Young's modulus indicating mechanical strength is 30000 kg / cm ² or more. Examples of materials that can maintain this strength include resins having excellent mechanical properties such as polyimide, polyethersulfone, polyetherketone, or polyetheretherketone. In particular, polyimide is preferable because it is easily available. The polyimide resin has a feature that the deformation of the belt at the time of driving is small as compared with a conventionally used thermoplastic resin.

  A polyimide resin is generally a polymer synthesized by condensation polymerization using tetracarboxylic dianhydride and diamine or diisocyanate as monomer components. Examples of the tetracarboxylic acid component of the dianhydride include pyromellitic acid, naphthalene-1,4,5,8-tetracarboxylic acid, naphthalene-2,3,6,7-tetracarboxylic acid, 2,3,5, 6-biphenyltetracarboxylic acid, 2,2 ', 3,3'-biphenyltetracarboxylic acid, 3,3', 4,4'-biphenyltetracarboxylic acid, 3,3 ', 4,4'-diphenyl ether tetracarboxylic acid Acid, 3,3 ′, 4,4′-benzophenonetetracarboxylic acid, 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic acid, 3,3 ′, 4,4′-azobenzenetetracarboxylic acid, bis ( 2,3-dicarboxyphenyl) methane, bis (3,4-dicarboxyphenyl) methane, β, β-bis (3,4-dicarboxyphenyl) propane, β, β-bis (3,4 Radical Po hydroxyphenyl) hex-off Oro propane.

  Examples of the diamine component include m-phenyldiamine, p-phenyldiamine, 2,4-diaminotoluene, 2,6-diaminotoluene, 2,4-diaminochlorobenzene, m-xylylenediamine, p-xylylenediamine, 1, 4-diaminonaphthalene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4'-diaminonaphthalebiphenyl, benzidine, 3,3-dimethylbenzidine, 3,3'-dimethoxybenzidine, 3,4 ' -Diaminodiphenyl ether, 4,4'-diaminodiphenyl ether (oxy-p, p'-dianiline; ODA), 4,4'-diaminodiphenyl sulfide, 3,3'-diaminobenzophenone, 4,4'-diaminophenyl sulfone, 4,4'-diaminoazobenzene, 4,4'-diamy Diphenylmethane, beta, beta-bis (4-amine phenyl) propane. The compound which substituted the amino group in the above-mentioned diamine component made into the said isocyanate component with the isocyanate group is mentioned. Commercially available products of these polyimides include, for example, pyromellitic acid-based polyimide (Kapton HA: manufactured by DuPont) having diamine as a diamine component, and 3,3 ′, 4,4′-biphenyltetracarboxylic acid-based polyimide (Upilex S: Ube Industries, Ltd.).

  Examples of the conductive agent dispersed in the base material include conductive carbon materials such as carbon black and graphite, metals or alloys such as aluminum and copper alloys, and tin oxide, zinc oxide, antimony oxide, indium oxide, and potassium titanate. , Conductive metal oxides such as antimony oxide-tin oxide composite oxide (ATO) and indium oxide-tin oxide composite oxide (ITO), lithium perchlorate, quaternary ammonium perchlorate, quaternary ammonium chloride One or two or more fine powders such as an electrolyte such as sodium trifluoromethanesulfonate are used. The metal oxide may be coated with insulating fine particles such as barium sulfate, calcium carbonate, and magnesium silicate.

  Among these conductive agents, carbon black is preferable in terms of price and environmental stability. Furthermore, from the viewpoint of dispersibility, a tin oxide composite oxide (product name: UF) with an average particle size of 0.1 μm manufactured by Mitsui Kinzoku Co., Ltd., a zinc oxide (Pastran Type-II) with 0.3 μm, Metal oxide with an average particle size of 1 μm or less, such as a barium sulfate surface with an average particle size of 0.4 μm coated with tin-based oxide (Pastran Type-IV), 0.2 μm ATO, 0.2 μm ITO, etc. Are also preferably used. The conductive metal oxide is preferably surface-treated with one or more silane coupling agents. Since the surface-treated metal oxide is improved in compatibility with the resin constituting the base material, the dispersion thereof becomes uniform and variation in the resistance value of the base material is suppressed.

  By the way, it is known that the expansion / contraction (displacement amount) of the belt due to the load during driving of the belt is inversely proportional to the Young's modulus of the belt material. That is, the relationship between the Young's modulus of the belt material and the amount of displacement due to the load when the belt is driven can be expressed by the following equation (1).

ΔL = α · P · L / (t · w · E) (1)
here,
ΔL: Belt displacement (μm)
α: Coefficient P: Load (N)
I: Belt length between two tension rolls (mm)
t: Belt thickness (mm)
w: Belt width (mm)
E: Young's modulus of belt material (N / mm ² )

Conventionally used thermoplastic resin materials such as PC and PVDF have a Young's modulus of 24000 kg / cm ² or less when carbon black is dispersed. In contrast, in this example, since the Young's modulus of the resin material of the surface layer (Ba) is increased to 30000 kg / cm ² or more, disturbances during driving of the belt (for example, the cleaning blade comes into contact with or separates from the belt surface). When the load fluctuations generated when the belts are the same), the belt stretch / shrinkage is reduced by 25% or more than the conventional one. Therefore, a high-quality transfer image can be obtained stably. In order to reduce the amount of displacement of the belt due to disturbance during driving of the belt and obtain a high-quality transfer image quality, the thickness of the belt is preferably 50 μm or more. If the belt becomes too thick, deformation of the belt surface at the portion of the tension roll will increase, and when forming a color image, the position of the multiple toner image will shift and color misregistration will occur. The thickness is preferably in the range of 50 to 300 μm, particularly 70 to 200 μm.

  When such a belt with excellent Young's modulus is used, when the parallelism of the secondary reference shaft deviates from the main reference, the tension roller tries to keep the position parallel to the drive roller to adjust the deviation. Variations in belt peripheral length elongation due to the generated tension deviation at the end of the tension roller can be suppressed. When the belt elongation varies and the circumferential length difference occurs, the belt shifting force increases or deteriorates. Accordingly, the fact that there is little variation in the belt circumferential length makes it possible to further reduce the belt shifting force. Therefore, by using a belt having an excellent Young's modulus, correction of the belt shift is performed more efficiently, and the occurrence of the belt shift is reliably suppressed.

As mentioned above, although this invention was demonstrated by the example of illustration, this invention is not limited to this.
For example, the present invention is not limited to the intermediate transfer type image forming apparatus as shown in FIG. 1, and may be a system in which a toner image is transferred from an image carrier onto a sheet while being conveyed while being held on a transfer conveyance belt. In this case, the belt unit is a transfer conveyance belt unit. The present invention can also be applied to a belt unit that simply conveys a sheet.

  The number of rollers for stretching the belt is not limited to two, and may be three or more. Moreover, the structure of the pressurization part in a tension roller is also arbitrary. Of course, the image forming apparatus is not limited to a printer, and may be a copying machine, a facsimile machine, or a complex machine thereof.

1 is a cross-sectional view illustrating a schematic configuration of a full-color printer which is an example of an image forming apparatus according to the present invention. It is an enlarged view showing in detail one of the image forming units. 2 is an external perspective view of an intermediate transfer belt unit. FIG. FIG. 5 is a perspective view showing the intermediate transfer belt in a non-displayed manner so that the internal configuration of the belt unit can be understood. It is a perspective view of a tension roller. It is an enlarged view which shows the edge part in detail. It is an enlarged view which shows the edge part of the side plate of a belt unit. It is an enlarged view which shows a mode that the tension roller was supported by the side plate. It is a schematic diagram which shows simply a mode that the belt unit was set to the main body apparatus and positioned. It is a schematic diagram for demonstrating the case where the shift | offset | difference arises in the parallelism of a secondary reference axis. It is a schematic diagram which shows a mode corrected so that the parallelism of a tension roller may be maintained by this invention. It is a schematic diagram which shows the state which looked at the belt unit from the side. It is the schematic diagram which looked at each roller of the belt unit from the A direction of FIG. It is a schematic diagram from the front which shows a mode that deviation occurred in the sub reference axis. It is the schematic diagram from the front which shows a mode corrected so that the parallelism of a tension roller might be maintained.

Explanation of symbols

10 Belt unit 20 Photosensitive drum (image carrier)
DESCRIPTION OF SYMBOLS 11 Intermediate transfer belt 12 Primary transfer roller 14,15 Side plate 16 Roller before transfer 21 Driving roller 22 Subordinate shaft 23 Tension roller 25 Pressure spring 26 Sliding protrusion 27 Sliding hole 60, 61 Positioning hole 62, 63 Reference hole

Claims (7)

In an image forming apparatus comprising a belt unit in which an endless belt is stretched on at least two support rollers including a driving roller and a tension roller, and positioning the belt unit with respect to a main body device by the shaft of the driving roller.
While setting the drive roller and the tension roller as two rollers with the longest distance in the belt circumferential direction among the support rollers on which the belt is stretched,
As a secondary reference for positioning the belt unit with respect to the main body device, a secondary reference shaft that penetrates between both side plates that support the drive roller and the tension roller is used, and the support roller is in a belt loop between the drive roller and the tension roller. An image forming apparatus provided separately . The image forming apparatus according to claim 1, wherein the tension roller is provided so as to be movable substantially parallel to an ideal position of the secondary reference shaft. The direction in which the tension roller is movable is a direction that is approximately ½ of the winding angle of the belt on the tension roller, and is substantially the same as the tension direction with respect to the belt. The image forming apparatus described in 1. The image forming apparatus according to claim 1, wherein the secondary reference shaft is disposed on or near a line connecting the shaft of the driving roller and the shaft of the tension roller. The image forming apparatus according to claim 1, wherein a base material of the belt is a polyimide resin. The image forming apparatus according to claim 1, wherein the belt unit is a transfer conveyance belt that transfers an image from an image carrier while holding and conveying a recording medium. The image forming apparatus according to claim 1, wherein the belt unit is an intermediate transfer belt that transfers an image from an image carrier and holds the transferred image onto a recording medium.

Images