JP2008070619A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which a part unsuitable for image-forming on a transfer belt is reduced so as to form an excellent image all the more even if the transfer belt and rollers for tensioning and laying the belt are downsized, and further (or) the number of rollers is reduced, and the belt having a joint or a weld part is adopted as the belt. <P>SOLUTION: In the image forming apparatus A for forming an image by using the transfer belt 3, the belt 3 has an image-forming proper area and an image-forming improper area including the joint and the weld part in a longitudinal direction, and also a position discrimination reference part RF is set on the belt 3. A toner image is primarily transferred to the image-forming proper area based on detection of the reference part RF by a detector SE. When stopping the belt 3, the belt 3 is stopped so that the image-forming improper area may be positioned on the roller 31 where the creep deformation of the belt part on the tensioning and laying roller becomes maximum when the belt is stopped out of the plurality of belt tensioning and laying rollers. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine combining two or more of these, and more particularly to an image forming apparatus that forms an image on a recording medium using a transfer belt.

  In an image forming apparatus such as an electrophotographic system, the surface of an electrostatic latent image carrier (hereinafter sometimes simply referred to as “image carrier”) is charged by a charging device, and an image exposure device or electrostatic device is charged in the charged area. An electrostatic latent image is formed according to an image to be formed by an electrostatic latent image forming device such as a recording device, and the electrostatic latent image is developed by a developing device to form a toner image. Then, the toner image is transferred to a recording medium, and the transferred toner image is fixed on the recording medium by heating and pressurizing with a fixing device.

Such image forming apparatuses can be roughly classified into a monochrome image forming apparatus and a color image forming apparatus (typically, a full color image forming apparatus) capable of forming an image using two or more colors of toner.
In a monochrome image forming apparatus, a toner image formed on an image carrier is directly transferred onto a recording medium using a transfer device, or is primarily transferred to an intermediate transfer member by a primary transfer device. The image is transferred from the transfer member onto the recording medium by a secondary transfer device and fixed by a fixing device. In some cases, the toner image formed on the image carrier is transferred to a recording medium held on a transfer body and then fixed on the recording medium.

  Known color image forming apparatuses include so-called four-cycle color image forming apparatuses and tandem color image forming apparatuses.

  A four-cycle color image forming apparatus forms an electrostatic latent image by charging the surface of an image carrier such as a photoconductor and exposing the image to the charged area. Develop to form a toner image. In such toner image formation, toner images of different colors are sequentially formed on the image carrier by sequentially using a plurality of developing units containing different color toners. Further, the toner image formed on the image carrier is sequentially transferred onto the intermediate transfer member by primary transfer using a primary transfer device, and the multiple toner images on the intermediate transfer member thus formed are subjected to secondary transfer. A color image can be obtained by secondary transfer to a recording medium with a transfer device and fixing with a fixing device. It is also possible to form an image using only one developing device or a plurality of developing devices smaller than the total number of developing devices.

  In a tandem type color image forming apparatus, an image carrier such as a photoconductor, a charging device for charging the surface thereof, an electrostatic latent image forming device such as an image exposure device, and the electrostatic latent image on the image carrier are developed. A plurality of image forming units including a developing device and the like are sequentially arranged along the intermediate transfer body according to the color of the toner, and a toner image formed on the image carrier in each image forming unit is a primary transfer device. Thus, the toner image is primary-transferred over the intermediate transfer member, and the multiple toner images on the intermediate transfer member are secondarily transferred to the recording medium by the secondary transfer device and fixed by the fixing device. It is also possible to form an image using only one image forming unit or a plurality of image forming units smaller than the total number of image forming units.

  In any of the above color image forming apparatuses, the toner image formed on the image carrier may be transferred to a recording medium held on a transfer body and then fixed on the recording medium.

  Regardless of whether the image forming apparatus is a monochrome image forming apparatus or a color image forming apparatus, the transfer body in an image forming apparatus that forms an image using a transfer body such as an intermediate transfer body or a transfer body that holds a recording medium includes a plurality of belt tension members. In many cases, a transfer belt that is wound around a pedestal roller and driven to rotate is employed.

  However, when the transfer belt is stopped for a long period of time, the portion of the transfer belt that is wound around the belt stretching roller is likely to be creep-deformed by the belt tension force, and the toner image is formed on the belt portion that has been creep-deformed during subsequent image formation. When the primary transfer toner image formed on the creep-deformed belt portion is secondarily transferred onto the recording medium, or the toner image is transferred to the recording medium held on the transfer belt, During transfer, between members involved in transfer, that is, between the image carrier and transfer belt in the case of primary transfer, between the transfer belt and recording medium in the case of secondary transfer, and in the case of transfer to a recording medium on the transfer body Insufficient adhesion tends to occur between the image carrier and the recording medium, which may lead to image omission.

  In this regard, for example, in Japanese Patent Application Laid-Open No. 9-222802, in a transfer unit in which an intermediate transfer belt is wound around a belt stretching roller, an image forming area on the belt for the maximum recording medium is defined between adjacent belt stretching rollers. It is described that a portion longer than the length is provided, and the belt portion where the image is formed is positioned at the portion when the belt is stopped, so that the image is not formed on the roller winding portion of the belt when the belt can be creep-deformed. Has been.

  In Japanese Patent Laid-Open No. 2000-305417, the use frequency of the intermediate transfer belt is stored in the storage unit, and the toner image transfer start position to the intermediate transfer belt is selected according to the use frequency stored in the storage unit. Thus, it is described that an image is formed on a belt portion with little creep deformation, and further, the intermediate transfer belt is rotated little by little during standby for image formation.

JP-A-9-222802 Japanese Patent Laid-Open No. 2000-305417

  However, the image forming apparatus described in Japanese Patent Application Laid-Open No. 9-222802 cannot meet the demand for downsizing and cost reduction of the image forming apparatus which has been rapidly progressing in recent years. In order to reduce the size and cost of the image forming apparatus, it is necessary to reduce the size of the transfer unit itself. For this purpose, it is necessary to reduce the size of the transfer belt and the belt stretching roller. In the described image forming apparatus, the transfer unit must be provided with a portion in which the distance between adjacent belt stretching rollers is equal to or longer than the length of the on-belt image forming area for the maximum recording medium. This hinders downsizing, and also prevents downsizing of the belt stretching roller.

  In order to reduce the size and cost of the image forming apparatus, it is required to reduce the size of the transfer belt and the belt stretching roller and to reduce the number of belt stretching rollers. For example, when two small-diameter rollers are employed as the belt stretching roller, the radius of each roller is small, and the center angle of the transfer belt around the roller is approximately 180 degrees, and the portion of the belt that is wound around the roller. The creep deformation when the belt stops is increased accordingly.

  When the transfer belt and the belt stretching roller are reduced in size and the number of belt stretching rollers is reduced as described above, intermediate transfer is performed as described in JP-A-2000-305417. Even if the toner image transfer start position to the intermediate transfer belt is selected according to the belt usage frequency or the intermediate transfer belt is rotated little by little during image formation standby, image defects such as missing images may occur. is there.

  Although it is conceivable to add a mechanism that does not cause creep deformation of the transfer belt, this increases the cost of the image forming apparatus.

The transfer belt has the following problems in addition to the above-described problems related to the creep deformation of the belt.
In other words, in order to reduce the cost of the image forming apparatus, a transfer belt with a seam or a resin material is used as a mold as in the case of adopting a transfer belt in which a sheet material is bent into a cylindrical shape and both ends of the sheet material are joined. In a transfer belt having a weld portion where a resin material or the like flows in a different direction from a different direction and meets each other, such as a transfer belt formed by pouring into a mold, such a joint or weld portion has characteristics (typical In particular, it is often changed with respect to other portions of the belt in terms of resistivity, thickness, and surface roughness. When a toner image is transferred using such a seam or weld having changed characteristics, image defects are likely to occur. Therefore, it is desirable not to transfer the toner image to the belt region having such a seam or weld.

  However, in order to reduce the size and cost of the image forming apparatus, if the size of the transfer belt or the belt stretching roller is reduced, and / or if the number of belt stretching rollers is reduced, the creep or belt joints described above are reduced. Or the belt part unsuitable for image formation by a weld part will increase.

  Therefore, the present invention forms an electrostatic latent image on an electrostatic latent image carrier, develops the electrostatic latent image to form a toner image, and winds the toner image around a plurality of belt stretching rollers. An image forming apparatus that transfers to a recording medium using a transfer belt, and the transfer belt and belt stretching roller are downsized to reduce the size and cost of the image forming apparatus, and / or Even if a transfer belt having a seam or a weld is used as the transfer belt by reducing the number of the gantry rollers, a portion that is not suitable for image formation on the transfer belt is suppressed to a small extent (in other words, the transfer belt is formed). It is an object of the present invention to provide an image forming apparatus capable of forming a good image as much as possible so that a portion suitable for an image is not narrowed.

  In order to solve the above problems, the present invention provides the following first and second image forming apparatuses. Each of these image forming apparatuses forms an electrostatic latent image on an electrostatic latent image carrier, develops the electrostatic latent image to form a toner image, and winds the toner image around a plurality of belt stretching rollers. The image forming apparatus transfers the image onto a recording medium using a hung transfer belt.

(1) First image forming apparatus An electrostatic latent image is formed on an electrostatic latent image carrier, the electrostatic latent image is developed to form a toner image, and the toner image is carried by the electrostatic latent image carrier. An image forming apparatus that performs primary transfer from a body to a transfer belt wound around a plurality of belt stretching rollers, and secondarily transfers a primary transfer toner image on the transfer belt from the transfer belt to a recording medium; The transfer belt has an image forming qualifying region and an image ineligible region along the longitudinal direction, and a position identification reference part is set, and a detector for detecting the position identification reference part is provided. Based on the detection of the position identification reference part by the detector, the image forming operation start timing is controlled so that the toner image on the electrostatic latent image carrier is primarily transferred to the image forming eligible area. When the transfer belt is stopped, the image ineligible area is the plurality of stretchers. An image forming apparatus in which the stop of the transfer belt is controlled so as to be positioned on the roller where the creep deformation of the upper belt portion of the stretch roller becomes the largest when the transfer belt is stopped.

(2) Second image forming apparatus.
An electrostatic latent image is formed on the electrostatic latent image carrier, the electrostatic latent image is developed to form a toner image, and the toner image is transferred from the electrostatic latent image carrier to a plurality of belt stretching rollers. An image forming apparatus for transferring to a recording medium held on a wound transfer belt, the transfer belt having an image forming eligible area and an image forming inadequate area for holding the recording medium along the longitudinal direction. And a position identification reference part is set, and a detector for detecting the position identification reference part is provided, and the position identification reference part is held in the image forming eligible area based on the detection of the position identification reference part by the detector. The image forming operation start timing is controlled so that the toner image on the latent electrostatic image bearing member is transferred to the recorded recording medium. When the transfer belt stops among the rollers, Image forming apparatus said transfer belt stop is controlled such that the creep deformation of La on the belt portion located closest larger roller on.

  In both the first and second image forming apparatuses, the “image ineligible area” of the transfer belt means that, for example, at least one of belt characteristics such as belt resistivity, thickness and surface roughness is transferred. This is an area that changes with respect to other areas of the belt (image formation eligible area). Such image ineligible areas are typically areas including seams or welds found, for example, in low cost transfer belts, and more specifically, the seams or welds and subsequent seams or welds. It is a neighborhood region of. Here, the “seam” is a joint portion of the transfer belt in which, for example, the sheet material is bent into a cylindrical shape and both ends of the sheet material are joined, and the “weld portion” is, for example, a resin material or the like in a mold As in a transfer belt formed by pouring into a mold, a resin material or the like flows from another direction in the mold and is abutted and intersected.

  According to the first image forming apparatus of the present invention, the toner image on the electrostatic latent image carrier is primarily transferred to the image forming eligible area based on the detection of the belt position identification reference portion by the detector. The image forming operation start timing of the image forming apparatus is controlled, and when the transfer belt is stopped, the image formation inadequate area is the creep deformation of the upper belt portion of the tension roller when the transfer belt is stopped among the plurality of tension rollers. The stop of the transfer belt is controlled so as to be positioned on the roller which becomes larger.

  According to the second image forming apparatus of the present invention, the toner image on the electrostatic latent image carrier is transferred to the recording medium held in the image formation eligible area based on the detection of the belt position identification reference portion by the detector. As described above, the image forming operation start timing of the image forming apparatus is controlled, and when the transfer belt is stopped, the image formation inadequate area is a region of the upper belt portion of the stretching roller when the transfer belt is stopped among the plurality of stretching rollers. The stop of the transfer belt is controlled so as to be positioned on the roller having the largest creep deformation.

  As described above, in both the first and second image forming apparatuses, the belt image inadequate area is arranged on the roller having the largest creep deformation when the belt is stopped. The portions are concentrated on the image formation inadequate area. Accordingly, when viewed as the entire belt, a portion that is not suitable for image formation on the transfer belt is suppressed and a good image can be formed.

  In order to reduce the size and cost of the image forming apparatus, the transfer belt and the belt stretching roller are reduced in size, and / or the number of belt stretching rollers is reduced, and the transfer belt has a seam or a weld portion. Even when such a low-cost transfer belt is employed, it is possible to suppress a portion that is not suitable for image formation on the transfer belt and to form a better image.

  In any of the first and second image forming apparatuses, the transfer belt position identification reference portion forms, for example, a hole detectable by an optical sensor in the ear of the transfer belt, or light detectable by the optical sensor. It may be provided by forming a reflection mark or the like, but it may be set in the image formation inadequate area itself having a different thickness, resistivity, surface roughness, etc. with respect to other portions of the transfer belt (that is, The position identification reference part may be an image ineligible area itself.)

In either of the first and second image forming apparatuses, the plurality of stretching rollers may be configured such that, for example, the plurality of belt stretching belts have the largest creep deformation of the upper belt portion of the stretching roller when the transfer belt is stopped. A roller having the smallest roller diameter among the rollers or a roller having the largest belt winding center angle among the plurality of belt stretching rollers can be exemplified.
A roller having the smallest roller diameter and the largest belt winding center angle can be exemplified as a roller having the largest creep deformation.

  Each of the first and second image forming apparatuses may be a color image forming apparatus such as the above-described 4-cycle type or tandem type, or may be an image forming apparatus dedicated to monochrome.

  As described above, according to the present invention, an electrostatic latent image is formed on an electrostatic latent image carrier, the electrostatic latent image is developed to form a toner image, and the toner image is stretched over a plurality of belts. An image forming apparatus that transfers to a recording medium using a transfer belt wound around a roller, and the transfer belt and belt stretching roller are downsized to reduce the size and cost of the image forming apparatus, and (Or) Even if the number of belt stretching rollers is reduced and a transfer belt having a seam or a weld is used as the transfer belt, the number of portions that are not suitable for image formation on the transfer belt is suppressed to be small ( In other words, it is possible to provide an image forming apparatus capable of forming a good image as much as possible so that a portion suitable for image formation is not narrowed.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows an example of an image forming apparatus according to the present invention. An image forming apparatus A in FIG. 1 is a four-cycle type color image forming apparatus. The image forming apparatus A includes a drum-type photoconductor 11 that is driven to rotate. A charging device 12, a developing device 14, an intermediate transfer belt 3 and a cleaning device 15 are arranged around the photosensitive member 11 in this order.

  The developing device 14 includes a yellow developing unit Y, a magenta developing unit M, a cyan developing unit C, and a black developing unit K. These developing units are mounted on a rotating developer unit rack 140 at equal central angular intervals. Yes. Each developing device has a developing roller 141.

  The intermediate transfer belt 3 is wound around the belt transfer rollers 31, 32, 33, and 34 and the primary transfer roller 2 that also serves as the belt transfer roller. The roller 31 is a driving roller, the roller 32 is a driven roller that faces the driving roller 31, the roller 33 is a tension roller that applies tension to the belt, and the roller 34 moves the belt 3 together with the primary transfer roller 2 to the photosensitive member 11. It is a roller made to contact with.

  The intermediate transfer belt 3 can be rotated counterclockwise in the figure (in the direction of the arrow in the figure) by a roller 31 that is rotationally driven by the belt drive unit 30. The belt 3 and the belt stretching roller (roller 31 and the like) constitute a transfer unit 300. The transfer unit 300 will be further described later.

  The secondary transfer roller 5 is provided for the belt portion wound around the driving roller 31, and the cleaning device 4 is provided for the belt portion wound around the driven roller 32.

  A timing roller pair 6 is provided below the secondary transfer roller 6, and a fixing device 8 is provided above. A cassette 7 for storing a recording medium (recording paper S in this example) is disposed below the developing device 14 and the like, and an image exposure device 13 is disposed above the cassette 7.

  According to the image forming apparatus A, a monochrome image can be formed using any one of the four developing devices, and a color image can be formed using two or more developing devices. Hereinafter, an example of forming a full-color image using four developing units Y, M, C, and K will be described.

  First, the developing device rack 140 is rotated so that the developing roller 141 of the yellow developing device Y faces the photoconductor 11, and the photoconductor 11 is rotated by a photoconductor drive motor (not shown) and the surface thereof is charged by the charging device 12. Charge. Further, image exposure for forming a yellow electrostatic latent image is performed from the image exposure device 13 on the charged area on the surface of the photoconductor based on image information provided from a computer (not shown) or the like. As a result, a yellow electrostatic latent image is formed on the photoconductor 11, and this is developed by the developing roller 141 of the developing unit Y to which a developing bias is applied from a power supply (not shown) to form a yellow toner image. The yellow toner image is primarily transferred onto an intermediate transfer belt 3 that is rotationally driven by a primary transfer roller 2 to which a primary transfer voltage is applied from a power supply (not shown).

  Similarly, a magenta toner image is formed using the magenta developing device M, transferred to the belt 3, a cyan toner image is formed using the cyan developing device C, transferred to the belt 3, and the black developing device K is used. Thus, a black toner image is formed and transferred to the belt 3. The timing of the formation of each color toner image and the primary transfer to the belt 3 is the timing at which these toner images are transferred onto the belt 3 in a superimposed manner. During the formation of the multiple toner image on the belt 3, the secondary transfer roller 5 and the cleaning device 4 are separated from the belt 3.

  On the other hand, the recording paper S accommodated in the cassette 7 is pulled out by the paper feed roller 71 and sent to the timing roller 6. The timing roller pair 6 supplies the recording paper S to the secondary transfer area in accordance with the movement of the multiple toner images on the belt 3 to the secondary transfer area. In the secondary transfer area, the secondary transfer roller 5 is moved to the belt 3 side before the arrival of the recording paper, and thus the secondary transfer voltage is applied to the multiple toner image on the belt 4 from a power supply (not shown). Then, the toner image is secondarily transferred onto the recording sheet S by the secondary transfer roller 5. The recording paper S then passes through the fixing device 8 so that the toner image is fixed under heat and pressure, and is discharged to the paper discharge tray T.

  Transfer residual toner or the like remaining on the photoreceptor 11 after the primary transfer is removed and cleaned by the cleaning device 15, and transfer residual toner or the like remaining on the belt 3 after the secondary transfer is removed and cleaned by the cleaning device 4.

  The intermediate transfer belt 3 is provided with a position identification reference portion RF (see FIG. 2), and a reference portion detector SE is provided so as to face the traveling track of the reference portion RF. As the position identification reference portion RF and its detector SE, for example, as shown in FIG. 2A, a through hole h formed in the ear portion of the belt 3 as the reference portion RF is used as the detector SE. An optical sensor comprising a light projecting element disposed on both sides of the ear portion and a light receiving element for receiving light from the light projecting element can be mentioned.

  In addition, as shown in FIG. 2B, the light reflection mark rs formed on the surface of the ear portion of the belt 3 as the reference portion RF is used as the detector SE so as to face the traveling track of the mark rs. An optical sensor including a light projecting element that can project light and a light receiving element that receives reflected light from the mark rs can be exemplified.

  Information detected by the detector SE of the position identification reference unit RF is input to the control unit 9 that controls the operation of the image forming apparatus (including the operation of the belt driving unit 30). The image formation position on the transfer belt 3 and the stop position of the transfer belt 3 are always kept constant by starting image formation after a predetermined time from the timing of detecting the reference portion RF by SE or stopping the rotation of the transfer belt 3. be able to. Further, by making the image forming position on the belt 3 constant, it is possible to clearly distinguish the image forming area and the non-image forming area in the rotation direction on the transfer belt 3. This will be explained later.

  The intermediate transfer belt 3 will be further described. For example, a low-cost belt 3 with a joint is used as the intermediate transfer belt 3 here. That is, a sheet-like material is bent into a cylindrical shape and bonded by pressurizing and heat-treating both ends of the sheet material, or by adhering using an adhesive. It is what has become.

  In many cases, at least one of belt characteristics such as thickness, resistivity, surface roughness, and the like in the seam in the belt 3 and the vicinity thereof is greatly changed with respect to other areas in the belt 3. And the adjacent area that follows it is an image formation inadequate area, and it is better not to transfer the toner image to that area. When the toner image is transferred to such an area, image defects are likely to occur.

  The intermediate transfer belt 3 may be formed of a resin or the like instead of being formed from a sheet material. For example, a belt formed by pouring a resin material or the like into a cylindrical mold can also be used. However, in the molding of such a belt, the material injected into the mold flows along the mold, but the portion farthest in the circumferential direction from the material injection port of the mold is in the mold. The material that has flowed from the two directions finally crosses to form a weld. Even in belt molding using a mold provided with a plurality of material injection ports, a weld portion where the materials intersect is formed.

  In such a welded portion and the adjacent region thereof, at least one of belt characteristics (thickness, resistivity, surface roughness, etc.) often varies greatly with respect to other portions of the belt. It is better not to transfer the toner image to the image formation inadequate area. When the toner image is transferred to such an area, image defects are likely to occur.

  Although it is conceivable to strictly manage the temperature management accuracy and cooling time in the mold in order to suppress the characteristic value fluctuation of the weld portion, this causes an increase in belt cost and a decrease in productivity. Also, when a product having a large variation in the characteristic value of the weld portion is regarded as a defective product, the yield in the factory is lowered, leading to a reduction in belt productivity and an increase in cost. Therefore, it is desirable that a transfer belt having a weld portion can be used.

In any case, as the material of the transfer belt 3, carbon is dispersed in polyphenylene sulfide (PPS) resin, and the surface resistivity is in the range of about 1 × 10 ⁷ Ω / □ to 1 × 10 ¹² Ω / □. What was adjusted to can be illustrated.

  In addition, polycarbonate (PC) resin, polyimide (PI) resin, urethane resin, fluorine resin, nylon resin and other elastic materials such as silicon rubber and urethane rubber, and conductive powder and carbon You may use the material which adjusted resistance by disperse | distributing.

The belt tension roller is a metal roller mainly made of aluminum or iron, or the outer peripheral surface of the core metal is made by dispersing conductive powder or carbon in an elastic material such as EPDM, NBR, urethane rubber, or silicon rubber. Examples thereof include those coated with a material whose resistance value is adjusted to 1 × 10 ⁹ Ω · cm or less.

Examples of the toner used in the developing device include polymerized toner having a particle diameter of 7 μm or less, more preferably 4.5 μm or more and 6.5 μm or less. A pulverized toner may be used.
The developing system of each developing device may be a so-called one-component developing system using a developer mainly composed of toner or a so-called two-component developing system using a developer mainly composed of toner and carrier.

  By the way, generally speaking, it is desirable that the transfer unit be reduced in size and cost by reducing the volume in order to reduce the size and cost of the image forming apparatus. For this purpose, a method of reducing the number of stretch rollers or reducing the diameter is most effective. However, at the portion where the transfer belt is wound around the belt stretching roller (drive roller, driven roller, tension roller, etc.) in the transfer unit, the force that deforms the transfer belt along the outer peripheral shape of the roller due to the belt tension force. In addition, when the image forming apparatus is stopped for a long period of time, the transfer belt remains creep-deformed, and in the next use, there is a possibility that an adhesion failure occurs at the transfer portion and an image omission occurs.

  Creep deformation increases as the belt-stretching roller becomes smaller in diameter and as the belt wrapping center angle around the roller becomes larger. Therefore, downsizing of the transfer unit is disadvantageous for creep of the transfer belt.

Also in the image forming apparatus A, the belt stretching roller 31 and the like are formed as small as possible in order to reduce the size and cost of the transfer unit 300. Therefore, this is a disadvantageous direction for creep of the transfer belt 3.
In addition, as in the transfer belt 3 in the image forming apparatus A, a belt that has a seam (or a weld portion or the like) so that the image formation eligible area and the image formation inadequate area can be clearly distinguished from each other. When the diameter of the laying roller is reduced and the winding center angle is increased, creep also occurs in the belt area other than the image ineligible area, and there is a possibility of image failure due to transfer omission due to the creep part. Further, due to the existence of an image ineligible region due to the joint (or weld portion) of the belt 3 and this creep, a belt portion not suitable for image formation increases.

  Therefore, in the image forming apparatus A, the control unit 9 places the image forming area on the photoreceptor 11 other than the image forming inappropriate area on the belt 3 based on the detection of the position identification reference unit RF by the detector SE. The image forming operation start timing of the apparatus A is controlled so that the toner image is primarily transferred, and the primary transfer timing of the toner image from the photoconductor 11 to the transfer belt 3 is controlled. The stop of the belt 3 is controlled so that the qualified region is located on the driving roller 31 where the creep deformation of the upper belt portion of the stretching roller is the largest.

  As described above, in the image forming apparatus A, the image formation inadequate area of the belt 3 is arranged on the driving roller 31 where the creep deformation becomes the largest when the belt is stopped. As a result, the belt portion that is not suitable for image formation is suppressed and the image can be formed as much as possible.

  Here, when the belt is stopped, the seam (or weld portion, etc.) of the belt 3 and the regions near both sides of the seam (or weld portion, etc.) are defined as image ineligible regions, and these are the rollers that have the largest creep deformation (this example) Then, it is desirable to wind around the driving roller 31).

For example, as shown in FIG. 3, the width of the belt seam (or weld portion) in the belt running direction is L [mm], the outer diameter of the maximum creep generating roller is D [mm], and the belt winding central angle around the roller Is θ, it is desirable that the width in the belt traveling direction of the image ineligible region is at least [L + (D × Π × θ ÷ 360)]. The control unit 9 stops the transfer belt in a state where at least a part of the width in the belt traveling direction of the image formation inadequate area is wound around the roller.
For example, if L = 20 mm, D = 20 mm, and θ = 160 degrees, the width in the belt traveling direction of the image ineligible region is desirably at least 76 mm [= 20 + (20 × Π × 160 ÷ 360)]. . The control unit 9 stops the belt 3 in a state where at least a part of the width of 76 mm is wound around the roller 31.

  The position of the position identification reference unit RF on the transfer belt 3, the installation position of the detector SE, the belt stopping method, and the like can be arbitrarily determined. In this example, the control unit 9 uses, for example, the position identification reference set for the belt 3. The belt drive unit 30 is controlled after waiting for the time required for at least a part of the image ineligible region to be wound around the roller 31 as described above after the part RF is detected by the detector SE. The belt 3 is stopped.

  In the image forming apparatus A, the driving roller 31 is a belt stretching roller that generates the maximum creep amount. However, depending on the case, the stretching roller that maximizes the creep amount changes. Here, as shown in FIG. 4, the creep amount is the displacement height when the belt surface can be displaced from the normal belt surface due to the belt extension due to creep.

  The tension roller that maximizes the creep amount has a smaller outer diameter and a larger belt winding amount (winding center angle) (provided that the belt tension is constant). As a specific example, a case where a stretching roller having an outer diameter of 30 mm or less and a winding angle of 90 degrees or more is an object can be mentioned. In many cases, the tension roller not included in this condition does not need to consider the effect of creep in practice. Further, it is often difficult to say that such a roller corresponds to the downsizing of the image forming apparatus.

  When the roller has an outer diameter of 30 mm or less and a winding angle of 90 degrees or more, the roller with the same outer diameter has the larger winding amount, and the roller with the same winding amount has the smaller outer diameter May be selected as a belt stretching roller that generates the maximum creep amount. For the rollers having different outer diameters and winding amounts, it is desirable to obtain an actual measurement value of the creep amount in each stretching roller, but a stretching roller having a smaller outer diameter may be selected. In some cases, the metal roller and the elastic material-covered roller may be selected as the metal roller.

  Regarding the position identification reference portion RF, the belt seam (or weld portion or the like) is different from that in the image formation eligible region in at least one of belt characteristics such as thickness, resistivity, and surface roughness. By using the seam (or weld part) as a position identification reference part, the detector has a resistivity, thickness, surface roughness, etc. that are different from the image forming eligible area at the seam (or weld part) as a detector. What can be detected may be adopted.

When detecting a change in resistivity, for example, by providing a member for energizing the transfer belt, applying a constant current thereto, monitoring the change in voltage value at that time, and detecting the change using a certain voltage value as a threshold, this part May be determined as a seam (or a weld portion, etc.), and control as described above may be performed based on the determination. In this case, the energization of the transfer belt 3 may be performed using a dedicated member, or may be performed using the primary transfer roller 2 or the secondary transfer roller 5.
FIG. 5 is a diagram illustrating the relationship between the belt position in the belt traveling direction and the surface resistance of the belt. It can be seen that the surface resistance of the seam (or weld) varies greatly with respect to other parts of the belt.

In detecting the thickness variation, for example, as shown in FIG. 6, a displacement sensor may be provided above the belt tension roller (roller 32 in FIG. 6) to detect the thickness variation.
In the case of detecting the surface roughness, for example, as in the case of detecting the mark rs, the reflectance variation on the surface of the helt 3 may be detected by an optical sensor.

  The four-cycle color image forming apparatus has been described above as an example, but the present invention can also be applied to a tandem type color image forming apparatus using an intermediate transfer belt, and can be applied to a monochrome image forming apparatus using a transfer belt. Is also applicable. Further, the present invention can be applied to a color image forming apparatus that holds a recording medium on a transfer belt and transfers a toner image onto the recording medium.

FIG. 7 shows an example B of a tandem type color image forming apparatus, and FIG. 8 shows another example C of a tandem type color image forming apparatus.
The apparatus B in FIG. 7 has a driving roller 31 ′ and an endless intermediate transfer belt 4 ′ wound around a roller 32 ′ facing the driving roller 31 ′. The transfer belt 4 'can be rotated counterclockwise in the figure (arrow direction in the figure) by a driving roller 31' driven by a belt drive unit (not shown).

  A cleaning device 8 'for cleaning secondary transfer residual toner and the like on the transfer belt 4' faces the belt portion on the counter roller 32 '. The secondary transfer roller 5 'faces the belt portion on the driving roller 31'.

  The surface layer portion of the secondary transfer roller 5 ′ is formed of an elastic material, and is pressed against the intermediate transfer belt 4 ′ by a pressing unit (not shown) to form a nip portion with the intermediate transfer belt 4 ′. It rotates following the rotation of the transfer belt 4 'or following the movement of the recording medium S fed into the nip as will be described later. A secondary transfer bias can be applied to the secondary transfer roller 5 ′ from a secondary transfer bias power supply device (not shown).

A timing roller pair 9 'is disposed below the secondary transfer roller 5', and a recording medium storage cassette that stores a recording medium (not shown) is further disposed below the pair of timing rollers 9 '.
A fixing device 6 ′ is disposed above the transfer roller 5 ′.

  The recording medium (recording paper S here) stored in the recording medium storage cassette can be pulled out one by one by a medium supply roller (not shown) and supplied to the timing roller pair 9 '.

  Between the rollers 31 ′ and 32 ′ around which the intermediate transfer belt 4 ′ is wound, the yellow image forming unit Y ′ and the magenta image forming unit M are moved along the transfer belt 4 ′ from the rollers 32 ′ to 31 ′. ', Cyan image forming portion C' and black image forming portion K 'are arranged in this order.

  Each of the image forming units Y ′, M ′, C ′, and K ′ includes a drum-type photoconductor 11 ′ as an electrostatic latent image carrier, and a charging device 12 ′ and an image exposure device are provided around the photoconductor. A device 13 ′, a developing device 14 ′, a primary transfer roller 2 ′, a cleaning device 15 ′ for removing and cleaning the primary transfer residual toner on the photosensitive member, and the like are arranged in this order.

The primary transfer roller 2 ′ is opposed to the photoconductor 11 ′ with the transfer belt 4 ′ in between, and rotates as the belt travels. A primary transfer bias for primary transfer of the toner image formed on the photoreceptor 11 ′ to the belt 4 ′ can be applied to the primary transfer roller 2 ′ from a primary transfer bias power supply device (not shown).
The exposure device 13 ′ can perform image exposure on the photoconductor 11 ′ using a laser beam in accordance with image information provided from a personal computer (not shown) or the like.

The photoconductor 11 ′ in each image forming unit can be driven to rotate clockwise in the drawing by a photoconductor drive motor (not shown).
A charging voltage can be applied to the charging device 12 ′ in each image forming unit at a predetermined timing from a charging power supply device (not shown).

  The developing device 14 ′ in each image forming unit can develop the electrostatic latent image formed on the photoreceptor 11 ′ with a developing roller 141 ′ to which a developing bias voltage is applied from a developing bias applying power supply device (not shown). it can.

According to the image forming apparatus B, an image can be formed using one or more of the image forming units.
Taking the case where a full color image is formed using all of the image forming portions as an example, first, a yellow toner image is formed in the yellow image forming portion Y ′, and this is primarily transferred to the transfer belt 4 ′.

  That is, in the yellow image forming portion Y ′, the photosensitive member 11 ′ is rotated in the clockwise direction in the drawing, and the charging area of the photosensitive member 11 ′ whose surface is uniformly charged to a predetermined potential by the charging device 12 ′. Then, image exposure for the yellow image is performed from the image exposure device 13 ′, and an electrostatic latent image for yellow is formed on the photoreceptor 11 ′. The electrostatic latent image is developed by a developing roller 141 ′ to which a developing bias of a developing device 14 ′ having yellow toner is applied to become a visible yellow toner image, and the toner image is transferred to a transfer belt by a primary transfer roller 2 ′. Primary transfer is performed on 4 '. At this time, a primary transfer bias voltage is applied to the primary transfer roller 2 ′ from a power supply device (not shown).

  Similarly, a magenta toner image is formed in the magenta image forming unit M ′ and transferred to the transfer belt 4 ′, and a cyan toner image is formed in the cyan image forming unit C ′ and transferred to the transfer belt 4 ′. A black toner image is formed at the forming portion K ′ and transferred to the transfer belt 4 ′.

  Yellow, magenta, cyan, and black toner images are formed at a timing at which these toner images are transferred onto the intermediate transfer belt 4 '. The multiple toner images formed on the transfer belt 4 'move toward the secondary transfer roller 5' by the rotation of the transfer belt 4 '.

  On the other hand, the recording paper S is pulled out from a recording medium storage cassette (not shown) by the medium supply roller, supplied to the timing roller pair 9 ', and is on standby.

  The recording sheet S waiting at the timing roller pair 9 ′ is supplied to the nip portion between the transfer belt 4 ′ and the secondary transfer roller 5 ′ in accordance with the multiple toner image sent by the intermediate transfer belt 4 ′. The multiple toner images are secondarily transferred onto the recording paper S by a secondary transfer roller 5 ′ to which a secondary transfer bias is applied from a power supply device (not shown).

  Thereafter, the recording medium paper S is passed through the fixing device 6 ′, where the multiple toner images are fixed on the recording paper S under heat and pressure. The recording sheet S is continuously discharged to a discharge tray by a discharge roller pair (not shown).

  The transfer residual toner and the like on the photoreceptor of each image forming unit are removed and cleaned by the cleaning device 15 ', and the transfer residual toner and the like on the intermediate transfer belt 4' are removed and cleaned by the cleaning device 8 '.

  In this image forming apparatus B, there are only two belt stretching rollers, a driving roller 31 ′ and a counter roller 32 ′, and the transfer unit including these rollers and the belt 4 ′ is downsized accordingly.

  Also in this image forming apparatus B, the transfer belt 4 ′ is a low-cost belt having a seam (or a weld portion), and the image forming eligible area and the image forming area along the longitudinal direction in the same manner as the transfer belt 3 in the image forming apparatus A. 7 has an image ineligible region including the seam (or weld portion, etc.), a position identification reference portion (not shown) is set, and a detector SE for detecting the position identification reference portion is shown in FIG. Are provided as illustrated in FIG.

  Then, based on the detection of the position identification reference portion by the detector SE, the image forming operation start timing of the apparatus B is such that the toner image on the photoreceptor 11 ′ of the image forming portion is primarily transferred to the image forming eligible region. As a result, the timing of toner image transfer from the photoreceptor 11 'to the transfer belt 4' is controlled.

  Further, when the belt 4 ′ is stopped so as not to narrow a portion suitable for image formation on the belt 4 ′, an image unacceptable region of the belt 4 ′ is detected based on detection of the position identification reference portion by the detector SE. The transfer belt is stopped so that is positioned on the roller 31 '.

  The stretching rollers 31 ′ and 32 ′ are rollers having the same outer diameter in this example, and both rollers have the same belt winding center angle (approximately 180 degrees), and the belt creep when the belt is stopped on any of the rollers. The deformation is the largest and the same. Here, the transfer belt 4 ′ is stopped so that the belt image ineligible region is positioned on the roller 31 ′.

  The apparatus B in FIG. 8 also has a drive roller 31 ″, a counter roller 32 ″, and an endless transfer belt 4 ″ wound around them. The transfer belt 4 ″ is counterclockwise in the figure (the direction of the arrow in the figure). Can be rotated. A cleaning device 8 ″ for cleaning secondary transfer residual toner and the like faces the belt portion on the opposing roller 32 ″.

  As will be described later, a voltage application roller 7 ″ for applying a voltage for attracting the recording medium S fed onto the belt 4 ″ to the belt 4 ″ faces the counter roller 32 ″. A timing roller pair 9 ″ is arranged upstream of the roller 7 ″ in the recording medium conveying direction, and a recording medium containing cassette containing a recording medium (not shown) is arranged below the pair of timing rollers 9 ″. In addition, a fixing device 6 ″ is disposed downstream of the drive roller 31 ″.

  Similarly to the apparatus B, the yellow image forming unit Y ″, the magenta image forming unit M ″, the cyan image forming unit C ″, and the black image forming unit K ″ are arranged in this order along the belt 4 ″.

  Each image forming unit includes a drum-type photoconductor 11 ″, and a charging device 12 ″, an image exposure device 13 ″, a developing device 14 ″, a transfer roller 2 ″, and a transfer on the photoconductor are provided around the photoconductor. A cleaning device 15 ″ for removing residual toner and cleaning is arranged in this order.

  The transfer roller 2 ″ faces the photoconductor 11 ″ with the transfer belt 4 ″ in between, and rotates following the running of the belt. A toner image formed on the photoconductor 11 ″ is transferred to the transfer roller 2 ″. A transfer bias for transferring to a recording medium on the belt 4 ″ can be applied from a power supply (not shown).

  The image forming apparatus C can also form an image using one or more of the image forming units. Hereinafter, a case where a full color image is formed using all of the image forming units will be described as an example.

  In the image forming apparatus C, the recording medium S is fed onto the belt 4 ″ at a predetermined timing by the timing roller pair 9 ″, and a suction voltage is applied to the belt 4 ″ by the voltage application roller 7 ″ in the middle. It is sucked and held, and is conveyed together with the belt 4 ″ to the fixing device 6 ″ under each image forming unit.

  On the other hand, in the yellow image forming portion Y ″, a yellow toner image is formed on the photoreceptor 11 ″ in the same manner as in the image forming portion Y of the apparatus B, and the toner image is transferred onto the transfer belt 4 ″ by the transfer roller 2 ″. Is transferred onto the recording medium S which is held and moved.

  Similarly, a magenta toner image is formed in the magenta image forming unit M ″ and transferred to the recording medium S, and a cyan toner image is formed and transferred to the medium S in the cyan image forming unit C ″. In FIG. 5, a black toner image is formed and transferred to the medium S. Yellow, magenta, cyan, and black toner images are formed on the recording medium S at the timing of transfer.

  The recording medium S on which the multiple toner images are thus transferred is passed through the fixing device 6 ″, where the multiple toner images are fixed to the recording paper S under heat and pressure. The recording medium S continues and is not shown. Are discharged to a discharge tray by a pair of discharge rollers.

  The transfer residual toner and the like on the photoreceptor of each image forming unit are removed and cleaned by the cleaning device 15 ″, and the toner and the like on the transfer belt 4 ″ are removed and cleaned by the cleaning device 8 ″.

  In this image forming apparatus C, there are only two belt-stretching rollers, a driving roller 31 ″ and a counter roller 32 ″, and the transfer unit including these rollers and the belt 4 ″ is downsized accordingly.

  Also in this image forming apparatus C, the transfer belt 4 ″ is a low-cost belt having a seam (or a weld portion or the like). Like the transfer belt 3 in the image forming apparatus A, the image forming eligible area and the transfer belt 4 ″ are arranged along the longitudinal direction. 8 has an image ineligible region including the seam (or weld portion) and a position identification reference part (not shown) is set, and a detector SE for detecting the position identification reference part is shown in FIG. Are provided as illustrated in FIG.

  Then, based on the detection of the position identification reference part by the detector SE, the toner image on the photoconductor 11 ″ of each image forming part is transferred onto the recording medium S held in the image forming eligible area. The image forming operation start timing is controlled.

  Further, when the belt 4 ″ is stopped so as not to narrow the portion suitable for image formation on the belt 4 ″, the image formation inadequate region of the belt 4 ″ is detected based on the detection of the position identification reference portion by the detector SE. The transfer belt is stopped so that is positioned on the roller 31 ″.

  The stretching rollers 31 ″ and 32 ″ are rollers having the same outer diameter in this example, and both rollers have the same belt winding center angle (approximately 180 degrees), and belt creep when the belt is stopped on any of the rollers. The deformation is the largest and the same. Here, the transfer belt 4 ″ is stopped so that the image forming inappropriate area of the belt is positioned on the roller 31 ″.

  INDUSTRIAL APPLICABILITY The present invention can be used to provide an image forming apparatus such as a copying machine, a printer, or a facsimile machine that forms an image on a recording medium using a transfer belt, or a combination machine that combines two or more of these.

1 is a diagram illustrating a schematic configuration of an example of a color image forming apparatus according to the present invention. FIG. 2 is a diagram illustrating an example of a position identification reference unit and a detector thereof on a transfer belt of a transfer unit in the image forming apparatus of FIG. 1. It is a figure which shows the roller in which the maximum creep amount generate | occur | produces, and the transfer belt part wound around it. It is a figure explaining the amount of creep. It is a figure which illustrates the relationship between each position of a transfer belt with a seam (or weld part) and belt surface resistance. It is a figure which shows the example of a detection of the thickness change of the seam (or weld part) in a transfer belt. 1 is a diagram illustrating an example of a tandem color image forming apparatus. It is a figure which shows the other example of a tandem type color image forming apparatus.

Explanation of symbols

A Image forming device 11 Photoconductor 12 Charging device 13 Image exposure device 14 Developing device Y Yellow developing device M Cyan developing device M Magenta developing device K Black developing device 140 Developing device rack 141 Developing roller 15 Cleaning device 2 Also serves as a belt stretching roller Primary transfer roller 300 Transfer unit 3 Intermediate transfer belt 31 Drive roller 32 Driven roller 33 Tension roller 34 Belt contact roller 30 Belt drive unit 4 Cleaning device 5 Secondary transfer roller 6 Timing roller pair 7 Paper feed cassette 8 Fixing device RF Position identification reference section SE provided on the belt 3 Detector h for detecting the position identification reference section Hole in belt ear (example of position identification reference section)
rs Light reflection mark (example of position identification reference part)
B, C Image forming apparatus Y ′, Y ″ Yellow image forming unit M ′, M ″ Magenta image forming unit C ′, C ″ Cyan image forming unit K ′, K ″ Black image forming unit 11 ′, 11 ″ Photoconductor 12 ', 12 "charging device 13', 13" image exposure device 14 ', 14 "developing device 141' developing roller 15 ', 15" cleaning device 2', 2 "primary transfer roller 31 ', 31" drive roller 32' , 32 "opposite roller 4 ', 4" intermediate transfer belt 5' secondary transfer roller 6 ', 6 "fixing device 8', 8" cleaning device 9 ', 9 "timing roller pair S recording medium

Claims (7)

An electrostatic latent image is formed on the electrostatic latent image carrier, the electrostatic latent image is developed to form a toner image, and the toner image is transferred from the electrostatic latent image carrier to a plurality of belt stretching rollers. An image forming apparatus that performs primary transfer onto a wound transfer belt and secondarily transfers a primary transfer toner image on the transfer belt from a transfer belt to a recording medium. The transfer belt is formed along a longitudinal direction. A position identification reference unit having an image qualifying region and an image ineligible region, a detector for detecting the position identification reference unit is provided, and the position identification reference unit by the detector Based on this detection, the image forming operation start timing is controlled so that the toner image on the electrostatic latent image carrier is primarily transferred to the image formation eligible area, and the image formation failure occurs when the transfer belt is stopped. The qualifying area is the transfer belt stop of the plurality of stretching rollers. Image forming apparatus characterized by the transfer belt stop is controlled such during creep deformation of the tension roller on the belt portion located closest larger roller on. An electrostatic latent image is formed on the electrostatic latent image carrier, the electrostatic latent image is developed to form a toner image, and the toner image is transferred from the electrostatic latent image carrier to a plurality of belt stretching rollers. An image forming apparatus for transferring to a recording medium held on a wound transfer belt, the transfer belt having an image forming eligible area and an image forming inadequate area for holding the recording medium along the longitudinal direction. And a position identification reference part is set, and a detector for detecting the position identification reference part is provided, and the position identification reference part is held in the image forming eligible area based on the detection of the position identification reference part by the detector. The image forming operation start timing is controlled so that the toner image on the latent electrostatic image bearing member is transferred to the recorded recording medium. When the transfer belt stops among the rollers, Image forming apparatus characterized by the transfer belt stop is controlled such that the creep deformation of La on the belt portion located closest larger roller on. The image forming apparatus according to claim 1, wherein the position identification reference portion of the transfer belt is set in the image formation inadequate area of the transfer belt. The roller having the largest creep deformation of the upper belt portion of the tension roller when the transfer belt is stopped among the plurality of tension rollers is a roller having the smallest roller diameter among the plurality of belt tension rollers. 2. The image forming apparatus according to 2 or 3. The roller having the largest creep deformation of the upper belt portion of the stretching roller when the transfer belt is stopped among the plurality of stretching rollers is a roller having the largest belt winding center angle among the plurality of belt stretching rollers. Item 5. The image forming apparatus according to any one of Items 1 to 4. 6. The image forming inadequate area of the transfer belt is an area in which at least one of resistivity, thickness and surface roughness of the transfer belt changes with respect to the image forming appropriate area of the transfer belt. The image forming apparatus according to any one of the above. The image forming apparatus according to claim 6, wherein the transfer belt has one of a joint and a weld portion, and the image formation inadequate region of the transfer belt includes either the joint or the weld portion. .