JP4298022B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic image forming apparatus.
[0002]
[Prior art]
In the electrophotographic color image forming apparatus, the image carrier is formed with a photosensitive layer composed of a charge generation layer and a charge transport layer on the surface of a metal drum or a metal belt. The area having the photosensitive layer on the surface of the metal drum or metal belt has a width greater than the maximum usable length of the surface.
[0003]
In the image forming apparatus, the image carrier is driven in a predetermined direction by a print start signal, and a bias is applied to a corona charger or a charging roller adjacent to the image carrier, whereby the surface of the image carrier is brought to a predetermined potential. Uniformly charged.
[0004]
Next, on the basis of the signal from the controller, the surface of the image carrier is irradiated with the laser light that is ON / OFF controlled in the longitudinal direction of the image carrier, for example, to convert the yellow color component of the image. Perform the corresponding exposure. The potential of the exposed portion on the surface of the image carrier is decreased, and an electrostatic latent image is formed as the potential decreased portion.
[0005]
Subsequently, the electrostatic latent image is developed with yellow toner by a developing device and visualized as a yellow toner image. The developing device carries yellow toner on the developing sleeve, regulates the layer thickness, transports it to the developing unit facing the image carrier, and applies a constant developing bias to the developing sleeve, thereby supporting the toner on the image. Transfer to and adhere to the electrostatic latent image on the body and develop the latent image.
[0006]
Next, the yellow toner image obtained by development is transferred onto the surface of an intermediate transfer member disposed adjacent to the image carrier (primary transfer). The intermediate transfer member includes a drum, a belt, and the like that move in the forward direction at substantially the same speed as the image carrier. By applying a transfer bias having a polarity opposite to that of the toner to the intermediate transfer member, The toner image is transferred onto the intermediate transfer member.
[0007]
After the primary transfer is completed, the remaining transfer toner on the surface is cleaned and removed by a cleaning member such as a blade, a roller, or a fur brush placed in contact with the image carrier, and then used for image formation of the next color. Is done.
[0008]
By repeating the above process for magenta, cyan, and black, a color image in which toner images of four colors are superimposed and transferred onto the intermediate transfer member can be obtained. After that, a transfer bias having a polarity opposite to that of the toner is applied to a secondary transfer unit such as a charging roller or a corona charger disposed opposite to the intermediate transfer member, and in this state, between the intermediate transfer member and the secondary transfer unit. By passing the transfer material, the four color toner images on the intermediate transfer member are collectively transferred to the transfer material (secondary transfer).
[0009]
The residual toner on the intermediate transfer member after the secondary transfer is removed by bringing a cleaner member such as a blade or a fur brush into contact with the intermediate transfer member, as in the cleaning of the image carrier.
[0010]
The transfer material onto which the toner image has been transferred is conveyed to a fixing device having a fixing roller and a pressure roller, and the transfer material is sandwiched between the fixing roller and the pressure roller and heated and pressed to thereby form the toner image. It is fixed on the surface of the transfer material. The fixing roller and the pressure roller are made of elastic rubber rollers. One or both of the core rollers are provided with a heater, and the temperature of the roller surface is controlled to a constant value by controlling the heater based on temperature detection means such as a contact thermistor. It is adjusted to become.
[0011]
Now, the length of the intermediate transfer member in the longitudinal direction is shorter than the length of the photosensitive layer of the image carrier in the longitudinal direction in order to prevent high-pressure leakage and secure sliding properties. In many cases, the intermediate transfer member is composed of a plurality of layers, but the upper layer portion is formed thin in order to suppress the occurrence of toner scattering, retransfer, etc., and the resistance and the like are strictly regulated. The lower layer portion of the intermediate transfer member is formed of a thick elastic body in order to increase the degree of adhesion with the image carrier, but in order not to affect the transferability in the upper layer portion, The resistance is smaller than that of the upper layer.
[0012]
At the end of such an intermediate transfer member, the lower layer portion is exposed at the end surface, so that when the high pressure is applied to the intermediate transfer member, if there is a defect on the surface of the image carrier, the resistance of the lower layer portion is reduced. Since it is low, there is a possibility of causing a high-pressure leak at the defective portion. If a high voltage leak occurs, the high voltage power supply in the image forming apparatus may be damaged. In order to avoid this, conventionally, a measure of winding an insulating tape around the entire circumferential surface of the end of the intermediate transfer member has been performed.
[0013]
[Problems to be solved by the invention]
However, the treatment of winding the insulating tape on the entire circumferential surface of the end portion of the intermediate transfer member is poor in durability and may be peeled off by rubbing against the image carrier. Further, when a belt member (intermediate transfer belt) is used as the intermediate transfer member, the belt is distorted in the longitudinal direction due to repeated passing of the transfer material to the belt, and the insulating tape is more easily peeled off.
[0014]
In addition, toner scattered during development sometimes adheres to the image carrier, and the toner adhered in the image forming region in the longitudinal direction of the image carrier is a cleaner member such as a blade disposed in contact with the image carrier. However, the toner adhering to the outside of the image forming area remains without being removed, and when the toner is transferred to the end of the intermediate transfer member, toner smearing occurs at the end of the intermediate transfer member. Since these edge stains are outside the image area, there is no problem in image quality. However, there are the following problems.
[0015]
In the intermediate transfer member of the belt member, small square holes (detection holes) are provided at regular intervals in the circumferential direction at the end of the belt (the region outside the maximum usable transfer material in the longitudinal direction). When the LED light-emitting element and light-receiving element of the detector are placed facing each other so that the end of the belt is sandwiched at an appropriate position, and when the belt starts to rotate when printing starts, the LED light-emitting element emits light and passes through the detection hole. The detected light is detected by the light receiving element, and the top signal (image formation start signal) is detected at this detection timing.
[0016]
The detection hole portion for detecting the top signal is also closed with a transparent insulating tape to prevent high-pressure leakage. However, if the end of the intermediate transfer member is contaminated with toner, the toner is applied to the insulating tape blocking the hole. As a result, the optical path of the detector is blocked, and it becomes impossible to detect the top signal, which makes it impossible to form an image.
[0017]
An object of the present invention is to provide an image forming apparatus capable of improving the durability of a high-pressure leak prevention member and stably preventing high-pressure leak at the end of an intermediate transfer member.
[0018]
Another object of the present invention is to provide an image forming apparatus capable of preventing toner smearing at the end of an intermediate transfer member by a high-pressure leak preventing member.
[0019]
[Means for Solving the Problems]
  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present inventionA drum-shaped image carrier that rotates while carrying a toner image, an intermediate transfer belt having a length in the longitudinal direction shorter than that of the image carrier, and a toner image transferred from the image carrier, and the intermediate transfer belt A secondary transfer means for transferring the toner image carried on the transfer material to a transfer material, a detection hole provided in a region at a longitudinal end of the intermediate transfer belt where the toner image is not transferred from the image carrier, and An optical detection member that emits light to the detection hole and detects light that has passed through the detection hole, and detects the position of the intermediate transfer belt according to the detection result of the optical detection member.
  AboveIntermediate transferbeltInsulating member having a size protruding outward from both longitudinal ends of the intermediate transfer belt between both longitudinal ends of the intermediate transfer belt and the opposing portions of the image carrierThe insulating member is fixed to the apparatus main body by a support member, and the surface facing the image carrier is a concave curved surface.The intermediate transferbeltThe intermediate transfer with the insulating member interposed at both endsWith beltThe image carrierButContactDoAn image forming apparatus characterized by the above.
[0020]
  According to the present invention, the intermediate transferbeltConsists of at least two or more layers, and the resistance of the layer in contact with the image carrier is made higher than the resistance of the layer below it. AboveThe insulating member is made of polyethylene terephthalate or polyacetal.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
  Examples according to the present inventionAnd reference examplesWill be described in more detail with reference to the drawings.
[0022]
  Reference example1
  FIG. 1 shows an image forming apparatus according to the present invention.Reference exampleFIG.
[0023]
  As shown in FIG.Reference exampleThe photosensitive drum 1 is used as the image carrier. As shown in FIGS. 2A and 2B, the photosensitive drum 1 has a structure in which a photosensitive layer composed of a charge generation layer 1b and a charge transport layer 1c is applied and formed on an aluminum cylinder 1a. This photosensitive layer is usually an insulator, but has the property of becoming a conductor when irradiated with light of a specific wavelength.
[0024]
To form an image, first, the photosensitive drum 1 is rotated, and in the course of the rotation, the surface of the photosensitive drum 1 is uniformly charged to a predetermined potential Vd (dark portion potential) by a charger. In this example, a charging roller 5 is used as a charger, and the charging roller 5 has a structure in which a metal core is covered with an elastic rubber layer.
[0025]
The charging roller 5 is brought into contact with the photosensitive drum 1 with an elastic rubber layer by pressurizing the protruding metal core portions at both ends with springs, and is driven to rotate with respect to the photosensitive drum 1. When a DC bias of a threshold value or more is applied to the core of the charging roller 5, a discharge is generated in the vicinity of the nip where the charging roller 5 and the photosensitive drum 1 are in contact with each other, whereby the DC bias applied to the surface of the photosensitive drum 1 is applied. Is charged with the same polarity as When the AC bias is applied simultaneously with the application of the DC bias, the surface of the photosensitive drum 1 can be more uniformly charged.
[0026]
Next, the exposure device 7 is used to irradiate the surface of the image carrier with light whose ON / OFF is controlled based on a signal from the controller in the longitudinal direction of the image carrier. The exposure corresponding to the yellow color component is performed. The exposed portion on the surface of the image carrier becomes a conductor, and the potential is lowered to Vl (bright portion potential), so that an electrostatic latent image is formed as a potential lowering portion.
[0027]
Subsequently, the electrostatic latent image is developed using yellow toner by the developing device 8a moved to the developing position facing the photosensitive drum 1. The yellow toner accommodated in the developing device 8a is negatively charged by friction with the members in the developing device 8a. A developing sleeve 9 generally made of a metal roller is installed in the developing unit 8a, and this developing sleeve 9 is disposed with a certain small gap (about 0.3 mm) with respect to the photosensitive drum 1, The photosensitive drum 1 is rotated at a circumferential speed difference of about 150% in the forward direction with respect to the rotation direction of the photosensitive drum 1. The negatively charged yellow toner in the developing device 8a is carried on the rotating developing sleeve 9, and is coated on a thin layer by being regulated by a developing blade.
[0028]
The toner coated with a thin layer is conveyed by a developing sleeve 9 to a developing unit facing the photosensitive drum 1. Then, a developing bias having an appropriate potential between the dark portion potential Vd and the bright portion potential Vl is applied to the developing sleeve 9 to generate an electric field between the photosensitive drum 1 and the developing sleeve 9, whereby the photosensitive drum 1. The toner on the developing sleeve 9 corresponding to the upper Vl portion is transferred to the photosensitive drum 1 and transferred to and adhered to the Vl portion, and the latent image is developed and visualized as a yellow toner image.
[0029]
The yellow developing unit 8a is mounted on the rotary 16, together with a developing unit 8b containing magenta toner, a developing unit 8c containing cyan toner, and a developing unit 8d containing black toner. Each of the developing devices 8a to 8d is sequentially moved to a developing position with the photosensitive drum 1 by the rotation of the rotary 16, and is used for developing a latent image on the photosensitive drum 1.
[0030]
The yellow toner image formed on the photosensitive drum 1 is then transferred to the surface of the intermediate transfer belt 4 that contacts the photosensitive drum 1 and rotates in the forward direction at substantially the same speed (primary transfer). The configuration of the intermediate transfer belt 4 and the transfer method there will be described later.
[0031]
After the primary transfer is completed, the remaining toner on the surface is removed by the cleaning blade 11 disposed in contact with the photosensitive drum 1, and the photosensitive drum 1 is used for image formation of the next color. The removed toner is stored in the waste toner chamber 6.
[0032]
In this example, the photosensitive drum 1, the charging roller 5, the cleaning blade 11, and the waste toner chamber 6 are configured as a cartridge (drum cartridge) that can be integrally replaced with the image forming apparatus main body.
[0033]
By repeating the above steps for three colors of magenta, cyan, and black, a color image in which toner images of four colors are superimposed and transferred onto the intermediate transfer belt 4 can be obtained.
[0034]
Thereafter, the secondary transfer roller 10 disposed opposite to the secondary transfer counter roller 15 with the intermediate transfer belt 4 interposed therebetween is brought into contact with the intermediate transfer belt 4, and a transfer bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 10. In this state, by passing a transfer material between the intermediate transfer belt 4 and the secondary transfer roller 10, the four color toner images on the intermediate transfer belt 4 are collectively transferred to the transfer material (secondary). Next transfer). The secondary transfer roller 10 includes a metal cored bar and a medium-resistance elastic body that covers the metal cored bar.
[0035]
The toner remaining on the intermediate transfer belt 4 after the secondary transfer is cleaned and removed by the cleaning blade 19 that is in contact with the rotational direction of the intermediate transfer belt 4 in the counter direction.
[0036]
The transfer material onto which the four color toner images have been transferred is conveyed to a fixing device 20 composed of a fixing roller 20a and a pressure roller 20b, and is driven to rotate in the forward direction at a constant speed, and the pressure roller 20b. It rushes into the nip part. The fixing roller 20a and the pressure roller 20b sandwich and heat and press the transfer material, thereby fusing the four color toners to complete a full-color toner image and fixing it on the surface of the transfer material. The transfer material that has passed through the nip and has been fixed is discharged out of the image forming apparatus through a paper discharge guide.
[0037]
The intermediate transfer belt 4 will be described in detail. The intermediate transfer belt 4 is wound around a tension roller 13, a drive roller 14, and the secondary transfer counter roller 15 and is supported with an appropriate tension. The drive roller 14 drives the intermediate transfer belt 4 in the forward direction. To be rotated. A primary transfer roller 12 is disposed in contact with the intermediate transfer belt 4 on the back surface of the contact portion of the intermediate transfer belt 4 with the photosensitive drum 1.
[0038]
The primary transfer roller 12 has a metal core and 10 covering it.^Five It consists of a low resistance elastic body of Ωcm or less. The toner constituting the toner image formed on the photosensitive drum 1 is generated between the photosensitive drum 1 and the primary transfer roller 12 by applying a positive DC bias having a polarity opposite to that of the toner to the primary transfer roller 12. The applied electric field is transferred to the surface of the intermediate transfer belt 4, and the toner image is transferred to the intermediate transfer belt 4.
[0039]
In this embodiment, the intermediate transfer belt 4 is made of rubber. As shown in FIG. 3, the intermediate transfer belt 4 basically has a low resistance rubber layer 4a as a base layer coated on a medium resistance surface layer 4b, and the base layer is a rubber layer 4a. This is for ensuring a sufficient contact nip between the photosensitive drum 1 and the intermediate transfer belt 4.
[0040]
The intermediate transfer belt 4 has a potential for preventing the toner image from being crushed and scattered due to the flow of charge from the dark portion potential portion Vd on the photosensitive drum 1 in the outer region of the toner image carrying portion on the surface thereof at the time of transfer. Barriers are formed. The surface layer 4b of the intermediate transfer belt 4 needs a certain amount of resistance in order to prevent the attenuation of the potential barrier, but if the resistance is too large, a voltage drop occurs. Insufficient electric field cannot be formed between them, and transfer failure occurs. Therefore, the resistance value of the surface layer 4b is strictly regulated.
[0041]
On the other hand, in order to prevent the rubber layer 4a from having an influence on the surface layer 4b whose resistance value is strictly controlled, the resistance value may be set to be almost conductive. As shown in FIG. 3, a metal core 4c is preferably embedded in the rubber layer 4a to prevent the intermediate transfer belt 4 from expanding and contracting. When the intermediate transfer belt 4 expands and contracts, the toner image transferred onto the intermediate transfer belt 4 is scattered by the shock, and the reproducibility of the image is reduced.
[0042]
As described above, the intermediate transfer belt 4 rotates in the forward direction with respect to the photosensitive drum 1, but the speed of the intermediate transfer belt 4 is 0.5 times faster than the photosensitive drum 1 in order to improve the efficiency of primary transfer. It is preferable to increase the speed about ˜2% so that a toner is mechanically scraped off when the toner image on the photosensitive drum 1 is transferred.
[0043]
The length of the intermediate transfer belt 4 in the longitudinal direction is shorter than the length of the photosensitive layer 1d in the photosensitive drum 1 in the longitudinal direction, as shown in FIG. This is because the slidability with respect to the intermediate transfer belt 4 is different between the region of the photosensitive layer 1d of the photosensitive drum 1 and the outer region thereof, and this acts as a resistance to the movement of the intermediate transfer belt 4 to rotate the intermediate transfer belt 4. This is to avoid unevenness, which may be caused.
[0044]
As described above, the photosensitive drum 1 is formed by applying and forming the insulating photosensitive layer 1d on the aluminum cylinder 1a. However, the photosensitive drum 1d has a problem in applying the photosensitive layer 1d, and the drum cartridge is attached to the apparatus main body. There may be a portion where the photosensitive layer 1d is thin on the photosensitive drum 1 due to a mistake or the like, or the aluminum cylinder is exposed without being formed at all.
[0045]
However, even if such a defect exists in the photosensitive drum 1, the surface layer 4 b of the intermediate transfer belt 4 has a high resistance, and therefore, by applying a high pressure to the primary transfer roller 12 except for the end of the intermediate transfer belt 4, No high pressure leak occurs between the intermediate transfer belt 4 and the photosensitive drum 1.
[0046]
However, at the end of the intermediate transfer belt 4, the rubber layer 4a is exposed at the end surface. The exposed rubber layer 4a is in a state close to the photosensitive layer 1d of the photosensitive drum 1 because the surface layer 4b of the intermediate transfer belt 4 is very thin. The resistance of the rubber layer 4a is low. For this reason, if a defect on the photosensitive drum 1 is located at a portion corresponding to the end portion of the intermediate transfer belt, a high-pressure leak may occur between the primary transfer roller 12 and the photosensitive drum 1 when a high pressure is applied. There is sex. When such a high-voltage leak occurs, there is a risk that the high-voltage power supply in the image forming apparatus may be damaged.
[0047]
  So bookReference exampleIn this case, a sheet 21 of polyethylene terephthalate (PET), which is an insulating material, is disposed between each of both ends in the longitudinal direction of the intermediate transfer belt 4 and the facing portion of the photosensitive drum 1, and the primary transfer roller 12 in FIG. The intermediate transfer belt 4 is brought into contact with the photosensitive drum 1 with the PET sheet 21 interposed between the end portions of the intermediate transfer belt 4 by the pressing of the intermediate transfer belt 4. This PET sheet 21 protrudes at least from the end of the intermediate transfer belt 4 to the outside and is formed in a width that covers the end, so that it does not move due to the rotation of the photosensitive drum 1 and the rotation of the intermediate transfer belt 4. The both ends of the PET sheet 21 in the moving direction of the intermediate transfer belt were fixed and supported by a support member (not shown) near the contact portion.
[0048]
Therefore, in the present invention, even if a defect on the photosensitive drum 1 is located at a portion corresponding to the end of the intermediate transfer belt 4, the end of the intermediate transfer belt 4 and the photosensitive drum 1 are directly connected by the PET sheet 21. Since there is no contact, no high-pressure leakage occurs between the intermediate transfer drum 4 and the photosensitive drum 1 due to the application of a high pressure to the primary transfer roller 12.
[0049]
  Further, since the PET sheet 21 is fixed to a support member outside the intermediate transfer belt 4, it is rubbed with the photosensitive drum 1 as it rotates as when an insulating tape is attached to the end of the intermediate transfer belt 4. The problem of peeling off does not occur. Further, since the PET sheet 21 is not attached to the intermediate transfer belt 4 like an insulating tape, a thicker sheet can be used, and the abrasion resistance against sliding against the photosensitive drum 1 and the intermediate transfer belt 4 can be used. Can be easily increased to achieve high durability.
  From the above, bookReference exampleAccordingly, high-pressure leakage at the end of the intermediate transfer belt 4 can be stably prevented.
[0050]
  Reference example2
  Other of the present inventionReference exampleWill be described with reference to FIG.
[0051]
  BookReference exampleThen, as shown in FIGS. 5A and 5B, a POM, which is a polyacetal resin, is used as a high-pressure leak preventing member (insulating member) between both end portions of the intermediate transfer belt 4 and the opposing portion of the photosensitive drum 1. A (polyoxymethylene) plate 22 was placed, fixed to a nearby support member, and supported immovably. The planar shape of the POM plate 22 and the arrangement in the longitudinal direction with respect to the end of the intermediate transfer belt 4 are as follows:Reference exampleThis is basically the same as the one PET sheet 21.
[0052]
  However, the POM plate 22 is made thick to some extent in order to increase the strength and increase the durability.RuThus, the length of the primary transfer roller 12 in the longitudinal direction is made shorter than the length of the intermediate transfer belt 4 in the longitudinal direction so that the POM plate 22 does not hit the primary transfer roller 21. The installation height of the POM plate 22 was set as follows.
[0053]
When the intermediate transfer belt 4 is pressed by the primary transfer roller 12 so that the intermediate transfer belt 4 is brought into contact with the photosensitive drum 1 to form a transfer nip, the end of the intermediate transfer belt 4 that is separated from the primary transfer roller 12 is also pulled. The POM plate 22 is pushed up and pushed up. In this state, the initial installation height of the POM plate 22 is set so that the POM plate 22 is in contact with the photosensitive drum 1 or not.
[0054]
If the arrangement of the POM plate 22 is too high, the POM plate 22 interferes to prevent the photosensitive drum 1 and the intermediate transfer belt 4 from coming into contact with each other, and the POM plate 22 is uniform between the photosensitive drum 1 and the intermediate transfer belt 4. When the transfer nip cannot be formed and the position of the POM plate 22 is too low, the end of the intermediate transfer belt 4 hits the POM plate 22 at a low position and is greatly distorted, and normal movement of the intermediate transfer belt 4 is hindered. Occurs.
[0055]
  BookReference exampleDepending onReference example1, the application of a high pressure to the primary transfer roller 12 does not cause a high-pressure leak between the intermediate transfer drum 4 and the photosensitive drum 1, and an insulating tape is attached to the end of the intermediate transfer belt 4. As is the case, there is no problem that the POM plate 22 is peeled off by sliding with the photosensitive drum 1 as it rotates, and the POM plate 22 can be made more durable.
[0056]
  Example1
  Of the present inventiononeAn embodiment will be described with reference to FIG.
[0057]
  Reference exampleAs described in 1 above, development is performed by applying a developing bias having an appropriate potential between the dark portion potential Vd and the bright portion potential Vl to the developing sleeve 9 to generate an electric field between the photosensitive drum 1 and the developing sleeve 9. As a result, the toner on the developing sleeve 9 corresponding to the Vl portion on the photosensitive drum 1 jumps to the photosensitive drum 1 and is transferred to the Vl portion.
[0058]
However, when this method is used, excessive toner may adhere to the Vd portion on the photosensitive drum 1 or the toner may not be sufficiently adhered to the Vl portion. If an AC bias is applied to the developing bias at the same time, the toner can be converged on the Vl portion while moving the toner back and forth between the developing sleeve 9 and the photosensitive drum 1 many times. It is possible to develop better than when a development bias of only components is applied. Therefore, in this embodiment, an AC + DC bias is used as the developing bias.
[0059]
However, when the AC component is added in this way, the toner easily scatters in the image forming apparatus while the toner moves back and forth between the developing sleeve 9 and the photosensitive drum 1, and a part of the toner is scattered. Adheres to the photosensitive drum 1.
[0060]
Since the toner adhering to the photosensitive drum 1 is removed by the cleaning blade 11 in the region excluding the end in the longitudinal direction, the toner adhering to the end of the photosensitive drum 1 is not a big problem. Since it is located outside the cleaning blade 11, it cannot be removed and remains as toner stains at the end of the photosensitive drum 1. For this reason, the toner may move from the end of the photosensitive drum 1 to the end of the intermediate transfer belt 4 in contact with the photosensitive drum 1. Since these edge stains are outside the image area, there is no particular problem with image quality.
[0061]
However, when the intermediate transfer method is employed as in the present embodiment, each color is accurately superimposed on the intermediate transfer belt 4, so that a mechanism that can accurately detect the position of the intermediate transfer belt 4 is usually used. The control is performed such that the exposure timing of the image is determined based on this.
[0062]
  In the present embodiment, small rectangular detection holes 23 are provided at regular intervals in the circumferential direction at one end of the intermediate transfer belt 4 (a region outside the maximum usable transfer material in the longitudinal direction) to transmit light. Type detector(Optical detection member)The LED light-emitting element and the light-receiving element are placed opposite to each other so that the end of the belt is sandwiched at an appropriate position, and when the belt starts rotating by starting the printing operation, the LED light-emitting element emits light and passes through the detection hole 23. The position of the intermediate transfer belt 4 is detected by detecting light with a light receiving element. Then, the top signal (image formation start signal) is detected at this detection timing. That is, the timing for starting image exposure is determined.
[0063]
The detection hole 23 is closed with a transparent insulating tape to prevent high-pressure leakage. When the end of the intermediate transfer belt 4 becomes dirty, the toner adheres to the insulating tape that blocks the detection hole 23, the optical path of the detector is blocked, and the top signal cannot be detected. It becomes impossible.
[0064]
Therefore, in this embodiment, the toner from the dirty end of the photosensitive drum 1 is confined to the high-pressure leak member so as not to be transferred to the intermediate transfer belt 4.
[0065]
  That is, as shown in FIGS. 6A and 6B, the high-pressure leak member is composed of a POM thick plate 24, and the POM thick plate 24 has a curvature substantially the same as the curvature of the peripheral surface of the photosensitive drum 1. A concave curved surface 25 was formed. The POM thick plate 24 is disposed between both end portions of the intermediate transfer belt 4 and the facing portion of the photosensitive drum 1 so that the curved surface 25 is along the peripheral surface of the facing portion of the photosensitive drum 1, and is supported nearby. Fixed to the member and supported immovably. The arrangement of the POM thick plate 24 in the longitudinal direction with respect to the end of the intermediate transfer belt 4 is as follows.Reference exampleThis is basically the same as the one PET sheet 21.
[0066]
According to this embodiment, the POM thick plate 24 can prevent high-pressure leakage at the end of the intermediate transfer belt 4, and in addition, a part of toner from the end of the photosensitive drum 1 can be removed from the POM thick plate. 24, since it can be confined within the curved surface 25, toner contamination at the end of the intermediate transfer belt 4 can be prevented well and can be greatly reduced.
[0067]
【The invention's effect】
  As described above, according to the present invention, intermediate transferbeltSince the insulating member is fixed to the surrounding supporting member and fixedly supported between the end of the image carrier and the facing portion of the image carrier, the intermediate transferbeltHigh-pressure leakage between the edge of the image and the image carrier, and intermediate transferbeltAs in the case where an insulating tape is attached to the end portion of this, there is no problem of being peeled off by sliding with the image carrier accompanying rotation, and the insulating member can be made more durable. . Therefore, intermediate transferbeltHigh-pressure leakage at the end can be stably prevented. In addition, a concave curved surface having substantially the same curvature as the peripheral surface of the image carrier is formed on the insulating member, so that the intermediate transferbeltAn insulating member is arranged at the opposite end of the image carrier and the image carrier, and the curved surface is arranged along the peripheral surface of the image carrier.By, Toner from the edge of the image carrier can be confined by the curved surface, intermediate transferbeltIt is possible to satisfactorily prevent toner contamination at the end of the toner.
[Brief description of the drawings]
FIG. 1 shows an image forming apparatus according to the present invention.Reference exampleFIG.
2 is a view showing a photosensitive drum installed in the image forming apparatus of FIG. 1; FIG.
3 is a cross-sectional view showing an intermediate transfer belt installed in the image forming apparatus of FIG. 1. FIG.
4 is a view showing an arrangement of a PET sheet as a high-pressure leak preventing member in the image forming apparatus of FIG. 1 between an end portion of an intermediate transfer belt and a facing portion of a photosensitive drum.
FIG. 5 shows another embodiment of the present invention.Reference exampleFIG. 2 is a diagram showing an arrangement of a POM plate as a high-pressure leak prevention member between an end portion of an intermediate transfer belt and a facing portion of a photosensitive drum.
FIG. 6 of the present inventiononeFIG. 3 is a diagram illustrating an arrangement of a POM thick plate as a high-pressure leak preventing member between an end portion of an intermediate transfer belt and a facing portion of a photosensitive drum in an embodiment.

Claims (4)

A drum-shaped image carrier that carries a toner image and rotates, an intermediate transfer belt that has a length in the longitudinal direction shorter than that of the image carrier, and onto which the toner image is transferred, and the intermediate transfer belt Secondary transfer means for transferring the toner image carried on the transfer material to a transfer material, a detection hole provided in a region at a longitudinal end of the intermediate transfer belt where the toner image is not transferred from the image carrier, and An optical detection member that emits light to the detection hole and detects light that has passed through the detection hole, and detects the position of the intermediate transfer belt according to the detection result of the optical detection member.
Between the both ends in the longitudinal direction of the intermediate transfer belt and the opposing portion of the image carrier, there is an insulating member having a size protruding outward from both ends in the longitudinal direction of the intermediate transfer belt, A surface that is fixed to the apparatus main body by a support member and that faces the image carrier is a concave curved surface, and the intermediate transfer belt and the intermediate transfer belt are interposed at both ends of the intermediate transfer belt via the insulating member. An image forming apparatus, wherein the image bearing member abuts.   The image forming apparatus according to claim 1, wherein the intermediate transfer belt includes a plurality of layers of at least two layers, and a resistance of a layer contacting the image carrier is higher than a resistance of a layer below the intermediate transfer belt.   The image forming apparatus according to claim 1, wherein the insulating member is made of polyethylene terephthalate. The image forming apparatus according to claim 1, wherein the insulating member is made of polyacetal.

Images