JP2007047287A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that toner dropping from an intermediate transfer belt falls and lies on an optical sensor to cause the faulty detection of a registration mark, consequently, color shift is not satisfactorily corrected in an image forming apparatus where the optical sensor is disposed vertically below a transfer belt unit. <P>SOLUTION: The optical sensor 18 is arranged to be spaced from an electrode roller 7 in a vertically downward direction adjacently to the electrode roller 7 in a main scanning direction SD. Voltage having a reverse polarity to toner is applied to the electrode roller 7 in appropriate timing. Since the toner drops while it is attracted to the electrode roller 7, it is restrained from falling and lying on the optical sensor 18. Therefore, the lowering of the detecting accuracy of the optical sensor 18 is restrained, thereby satisfactory correcting of the color shift can be attained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms a color image by superimposing toner images of different colors on the surface of an intermediate transfer belt, and to a technique for correcting color misregistration.

  The image forming apparatus includes a transfer belt unit including an intermediate transfer belt and a conveying unit that rotates and conveys the transfer belt in a predetermined conveying direction, and includes a plurality of image forming stations that form different toner images. It is arranged along the belt conveyance direction. A toner image formed at each image forming station is superimposed on the surface of the intermediate transfer belt to form a color image.

  As described above, color misregistration is one of the serious problems in an apparatus that forms a color image by superimposing a plurality of toner images of different colors on the surface of the intermediate transfer belt. This occurs when the transfer positions of a plurality of toner images of different colors to the intermediate transfer belt are shifted from each other, and appears as a change in color tone. Therefore, in order to solve this problem, a reference pattern image (hereinafter referred to as “registration mark”) for detecting color misregistration is formed on the intermediate transfer belt in advance, and each color toner obtained from position information of each registration mark Color misregistration is corrected based on the relative positional relationship of the images.

  As means for detecting the position information of such a registration mark, conventionally, an optical sensor that irradiates each registration mark with light and detects reflected light from each registration mark is known. Various proposals have been made regarding the arrangement position of such an optical sensor. For example, in Patent Document 1, an optical sensor is arranged below the transfer belt unit.

Japanese Patent Laid-Open No. 2002-6687 (FIG. 1)

  However, in an apparatus in which an optical sensor is disposed on the lower side of the transfer belt unit, the toner attached on the surface of the intermediate transfer belt may fall due to gravity and fall on the optical sensor. When toner accumulates on the optical sensor in this way, there is a problem that the detection accuracy of the optical sensor is lowered and good color misregistration correction cannot be performed.

  The present invention has been made in view of the above problems, and in an image forming apparatus in which an optical sensor is disposed below the intermediate transfer belt, it is possible to perform good color misregistration correction by suppressing toner from accumulating on the optical sensor. It aims to be.

  An image forming apparatus according to the present invention includes a transfer belt unit including a transfer belt having a plurality of layers including a conductive layer, a transport unit that rotates and transports the transfer belt in a predetermined transport direction, and a transfer belt along the transport direction of the transfer belt. A plurality of image forming stations arranged to form toner images of different colors by developing the latent images carried on the surface of the latent image carrier each having the same polarity, and a conductive layer of the transfer belt An electrode roller for transferring a toner image of a different color formed on the latent image carrier of each of a plurality of image forming stations onto the surface of the transfer belt by applying a voltage having a polarity opposite to that of the toner, and a transfer belt A transfer belt is formed on the surface of the transfer belt for correcting color misregistration between a plurality of image forming stations. An optical sensor that emits light to the toner image and detects light incident through the opposing surface, and the optical sensor is positioned so that the opposing surface is positioned in a vertically lower region of the transfer belt unit. In order to achieve the above object, the transfer belt is arranged in a strip shape having a predetermined width in the main scanning direction substantially orthogonal to the transport direction and is electrically short-circuited with the conductive layer. A voltage application region is provided at one end of the transfer belt, and the electrode roller is disposed in a vertically lower region of the transfer belt unit and applies a voltage to the conductive layer of the transfer belt in contact with the voltage application region. The optical sensor is characterized in that it is adjacent to the electrode roller in the main scanning direction and is spaced apart from the electrode roller in the vertically downward direction.

  In the invention configured as described above, in detecting the positional information of the toner image formed on the transfer belt surface for color misregistration correction, the invention has a facing surface facing the transfer belt surface, An optical sensor that emits light toward the toner image and detects light incident through the facing surface is used. Such an optical sensor is arranged so that its opposing surface is located in a vertically lower region of the transfer belt unit. Therefore, the toner adhered on the transfer belt may fall due to gravity and fall on the opposite surface of the optical sensor. In such a case, the light emitted from the optical sensor toward the toner image on the surface of the transfer belt or, conversely, the light incident on the optical sensor is scattered by the toner deposited on the opposite surface, and the detection accuracy of the optical sensor decreases. There is a case. However, in the present invention, the optical sensor is disposed adjacent to the electrode roller in the main scanning direction and spaced apart from the electrode roller in the vertically downward direction. Therefore, since the toner is prevented from falling on the optical sensor, it is possible to correct the color misregistration while suppressing a decrease in detection accuracy of the optical sensor. The reason for this will be described. In the image forming apparatus according to the present invention, a voltage having a polarity opposite to the toner polarity is applied to the conductive layer of the transfer belt by an electrode roller disposed in a vertically lower region of the transfer belt unit, so that the latent image of each image forming station has. The toner image formed on the surface of the image carrier is transferred to a transfer belt. Therefore, in the vicinity of the electrode roller, an electric field is generated in a direction that attracts toner toward the electrode roller. Therefore, in the present invention, the photosensor is disposed adjacent to the electrode roller in the main scanning direction and spaced apart from the electrode roller in the vertical downward direction, so that the toner above the photosensor falls from the transfer belt. However, the toner falls while being attracted to the electrode roller side. Therefore, it is possible to prevent the toner from falling on the opposite surface of the optical sensor and to perform good color misregistration correction.

  Further, a counter electrode may be provided on the counter surface of the photosensor, and the counter electrode may be biased to a GND potential or a potential having the same polarity as the toner. With this configuration, an electric field that attracts toner from the opposing surface of the photosensor to the electrode roller is reliably generated. Therefore, even when the toner above the optical sensor falls from the transfer belt, the toner falls while being more reliably attracted to the electrode roller side. Therefore, it is possible to effectively suppress the toner from falling on the opposite surface of the optical sensor, and to perform good color misregistration correction. In particular, when the counter electrode is biased to a voltage having the same polarity as that of the toner, a repulsive force is generated between the toner and the counter electrode, so that the accumulation of the toner on the photosensor facing surface can be more effectively suppressed. Good color misregistration correction becomes possible.

<First Embodiment>
FIG. 1 is a diagram showing a basic configuration of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. The apparatus 1 is an image forming apparatus that forms a full color image by superposing four color toners of black (K), cyan (C), magenta (M), and yellow (Y). In this image forming apparatus 1, when an image forming command is given to the main controller 51 from an external device such as a host computer, the engine controller 52 controls each part of the engine unit EG according to the command from the main controller 51. An image forming operation is executed, and an image corresponding to the image forming command is formed on a sheet S such as plain paper, thick paper, and an OHP transparent sheet.

  In FIG. 1, the image forming apparatus 1 of the present embodiment includes a housing body 2 and a paper discharge tray 4 provided on the upper surface of the housing body 2.

  In the housing main body 2, an electrical component box 5 containing a power circuit board, a main controller 51, and an engine controller 52 is provided. An image forming unit 6, a transfer belt unit 9, and a paper feed unit 10 are also disposed in the housing body 2. On the other hand, a secondary transfer unit 11, a fixing unit 12, and a sheet conveying mechanism 13 are disposed on the right side (right side in FIG. 1) of the transfer belt unit 9.

  The transfer belt unit 9 is stretched around a driving roller 14 that is rotationally driven by a driving motor (not shown), three driven rollers 151, 152, and 153, and these four rollers (conveying means), and is shown in an arrow direction D16 in the drawing. And an intermediate transfer belt 16 (transfer belt) that is driven to circulate. The driven roller 151 is disposed on the substantially horizontal left side of the driving roller 14 in FIG. 1 and functions as a tension roller that applies tension to the intermediate transfer belt 16. Further, the driven rollers 152 and 153 are arranged vertically below the drive roller 14 and the driven roller 151 and arranged substantially in the horizontal direction. Therefore, the belt surface 16a in which the belt conveyance direction D16 when the intermediate transfer belt 16 is driven is rightward (rightward in FIG. 1) is conveyed in a substantially horizontal direction with the surface thereof directed vertically downward. In the present embodiment, the belt surface 16a is a belt tension surface (surface pulled by the drive roller 14) during driving of the belt, and the peripheral speed is lower than the peripheral speed of the photosensitive drum (latent image carrier) 20 of each color. Have speed. In this way, by setting the peripheral speed of the intermediate transfer belt 16 to be slower than the peripheral speed of each photosensitive drum 20, the photosensitive drum 20 is pulled by the intermediate transfer belt 16 in a direction that suppresses rotation. Driving.

The drive roller 14 also serves as a backup roller for the secondary transfer roller 19. A rubber layer having a thickness of about 3 mm and a volume resistivity of 10 ⁵ Ω · cm or less is formed on the peripheral surface of the drive roller 14, and the illustration is omitted by grounding through a metal shaft 2. A conductive path of the secondary transfer bias supplied from the secondary transfer bias generator through the secondary transfer roller 19 is used. Thus, by providing the driving roller 14 with a rubber layer having high friction and shock absorption, it is difficult for the impact when the sheet S enters the secondary transfer portion to be transmitted to the intermediate transfer belt 16, and deterioration of image quality is prevented. can do.

  In the present embodiment, the driven roller 151 is also used as a backup roller for the cleaner blade 171. As shown in FIG. 1, the cleaner blade 171 abuts on the intermediate transfer belt 16 at the portion where the intermediate transfer belt 16 is wound around the driven roller 151 and remains on the surface of the intermediate transfer belt 16 after the secondary transfer. Clean and remove toner. The removed toner is collected in a waste toner box 172.

  The driving roller 14 and the driven rollers 151, 152, 153 are rotatably supported by a support frame (not shown) of the transfer belt unit 9. Further, an elastic member 21 is disposed on the back surface of the belt surface 16a facing the right in the transport direction of the intermediate transfer belt 16 so as to be opposed to the photosensitive drums 20 of image forming stations Y, M, C, and K, which will be described later. . These four elastic members ensure that the intermediate transfer belt 16 comes into contact with the photosensitive drums 20 of the image forming stations Y, M, C, and K with a required elastic force. In addition, a toner image is formed on the surface of the photosensitive drum 20 and the toner image is primarily transferred onto the surface of the intermediate transfer belt 16. Details of these are as follows. It will be described later.

  The image forming unit 6 includes image forming stations Y (for yellow), M (for magenta), C (for cyan), and K (for black) that form a plurality (four in this embodiment) of different color images. I have. Each image forming station Y, M, C, and K is provided with a photosensitive drum 20 (latent image carrier). Further, around each photosensitive drum 20, a charging roller 22, an image writing unit 23, a developing unit 24, and a photosensitive cleaner 25 are disposed. Then, a charging operation, a latent image forming operation, and a toner developing operation are executed by these functional units. In FIG. 1, since the image forming stations of the image forming unit 6 have the same configuration, for convenience of illustration, only some of the image forming stations are denoted by reference numerals, and the other image forming stations are omitted. . In this embodiment, the image forming stations Y, M, C, and K are arranged in this order from the upstream side to the downstream side in the belt conveyance direction D16.

  The photosensitive drums 20 of the image forming stations Y, M, C, and K are disposed so as to be in contact with the belt surface 16a facing the right in the transport direction of the intermediate transfer belt 16 at the primary transfer position TR1. Each of these photosensitive drums 20 is connected to a dedicated drive motor and is driven to rotate at a predetermined peripheral speed in the conveyance direction of the intermediate transfer belt 16 as indicated by an arrow D20 in the figure.

  The surface of the charging roller 22 is made of elastic rubber. The charging roller is configured to be driven to rotate in contact with the surface of the photosensitive drum 20 at a charging position, and at a peripheral speed in the driven direction with respect to the photosensitive drum 20 as the photosensitive drum 20 rotates. Followed rotation. The charging roller 22 is connected to a charging bias generator (not shown), and receives the charging bias from the charging bias generator to charge the surface of the photosensitive drum 20 at the charging position.

  The image writing unit 23 is an array writing in which elements such as a liquid crystal shutter including a light emitting diode and a backlight are arranged in a line in the axial direction of the photosensitive drum 20 (direction perpendicular to the paper surface of FIG. 1). The head is used and is spaced from the photosensitive drum 20. The array-like writing head has a shorter optical path length and is more compact than the laser scanning optical system. Therefore, it can be disposed close to the photosensitive drum 20 and has the advantage that the entire apparatus can be downsized.

  In this embodiment, the photoconductive drum 20, the charging unit 22, the developing unit 24, and the photoconductive cleaner 25 of each of the image forming stations Y, M, C, and K are replaced with replacement cartridges 6Y, 6M, 6C, and 6K (FIG. 2). ) As a unit. Each replacement cartridge 6Y, 6M, 6C, 6K is provided with non-volatile memories 91-94 for storing information relating to the replacement cartridge. The transmission / reception units 53Y, 53M, 53C, and 53K provided in each replacement cartridge and the transmission / reception units 522Y, 522M, 522C, and 522K provided on the main body side are arranged close to each other, and the CPU 521 and the memory of the engine controller 52 are arranged. Wireless communication is performed with 91-94. In this way, information regarding each replacement cartridge is transmitted to the CPU 521, and information in each of the memories 91 to 94 is updated and stored.

  Next, the developing unit 24 will be described on behalf of the image forming station Y. The developing unit 24 includes a toner supply roller 31 and a development roller 33 that contacts the toner supply roller 31 and the photosensitive drum 20 and rotates at a predetermined peripheral speed. Then, the toner stored in the developing unit 24 is supplied to the developing roller 33 by the toner supply roller 31. Then, at a development position where the development roller 33 and the photosensitive drum 20 are in contact with each other by a development bias applied to the development roller 33 from a development bias generator (not shown) electrically connected to the development roller 33, a predetermined polarity is provided. The charged toner thus charged moves from the developing roller 33 to the photosensitive drum 20, and the electrostatic latent image formed by the image writing unit 23 is visualized. In the present embodiment, negatively charged toner charged to negative polarity is used.

  Further, in this embodiment, a photoconductor cleaner 25 is provided in contact with the surface of the photoconductor drum 20 on the downstream side of the primary transfer position in the rotation direction D20 of the photoconductor drum 20. The photoconductor cleaner 25 is in contact with the surface of the photoconductor drum 20 to remove the toner remaining on the surface of the photoconductor drum 20 after the primary transfer.

Next, the structure of the intermediate transfer belt 16 will be described. FIG. 3 is a cross-sectional view of the intermediate transfer belt 16. As shown in FIG. 3, the intermediate transfer belt 16 is provided with a base layer 161 on its back surface (belt innermost circumference), and further has a conductive layer 162 and a covering layer 164 sequentially arranged toward the outer circumference side. ing. The covering layer 164 is made of a synthetic resin (for example, urethane resin) having a predetermined thickness (for example, 20 μm), and includes conductive particles (for example, SnO ₂ ) and fluororesin (for example, polytetrafluoroethylene) particles. By including the conductive particles, the resistance value of the coating layer 164 is set to about 10 ⁸ to 10 ¹⁴ Ω, and by including the fluororesin particles, the frictional resistance is suppressed and the intermediate transfer belt 16 is locked by the cleaner blade. Can be prevented. The conductive layer 162 is formed, for example, by vapor deposition of aluminum. The base portion 161 has a predetermined thickness (for example, 100 μm), and is formed of a synthetic resin such as PET (polyethylene terephthalate). Further, in the intermediate transfer belt 16 in FIG. 3, a belt electrode 165 is provided at the left end portion (left end portion in FIG. 3) of the intermediate transfer belt 16. The belt electrode 165 is formed by removing the coating layer 164 which is a layer on the outer peripheral side from the conductive layer 162 in a strip shape, and disposing a conductive member in the strip shape at the removed portion. Therefore, the belt electrode 165 and the conductive layer 162 are electrically short-circuited. Thus, in the present embodiment, the belt electrode 165 corresponds to the “voltage application region” of the present invention.

  As shown in FIG. 4, the electrode roller 7 is in contact with the belt electrode 165 formed as described above. In the present embodiment, as shown in FIG. 1, the electrode roller 7 is disposed between the image forming station K and the driven roller 153. That is, the electrode roller 7 is located in a region (vertical lower region) extending vertically below the transfer belt unit 9. The electrode roller 7 is connected to a primary transfer bias generator 525 (FIG. 2). Then, at an appropriate timing, a primary transfer bias voltage having a polarity opposite to that of the charged toner generated by the primary transfer bias generator 525 is applied to the conductive layer 162 via the belt electrode 165 by the electrode roller 7. In this embodiment, a voltage of +200 [V] is applied as the primary transfer bias. As a result, the toner images formed on the surface of the photosensitive drum 20 of each image forming station Y, M, C, K are primarily transferred onto the surface of the intermediate transfer belt 16 at the primary transfer position TR1.

  As shown in FIG. 1, an optical sensor 18 is installed in a vertically lower region of the transfer belt unit 9 on the support frame of the transfer belt unit 9. FIG. 5 and FIG. 6 are diagrams showing details of the arrangement position of the optical sensor 18, respectively. 5 is a diagram showing the positional relationship among the electrode roller 7, the transfer belt 16, and the optical sensor 18 when viewed from the direction X in FIG. 1, and FIG. 6 is viewed from the direction Y in FIG. 6 is a diagram showing the positional relationship among the electrode roller 7, the transfer belt 16 and the optical sensor 18 at the time. As shown in FIG. 5, in the present embodiment, the optical sensor 18 has its facing surface 181 facing the surface of the transfer belt 16 and is disposed vertically below the transfer belt 16. Further, as shown in FIGS. 5 and 6, the optical sensor 18 is adjacent to the electrode roller 7 in the main scanning direction SD substantially orthogonal to the belt conveying direction D16 and is spaced apart from the electrode roller 7 in the vertically downward direction. An optical sensor 18 is installed in the space. In this embodiment, a sensor backup roller 8 (FIGS. 1 and 4) is provided so as to face the opposing surface 181 of the optical sensor 18 via the transfer belt and contact the back surface of the transfer belt. As will be described later, the optical sensor 18 irradiates the surface of the intermediate transfer belt 16 with light to detect a registration mark formed on the surface. By providing such a sensor backup roller 8, the surface of the intermediate transfer belt 16 is detected. The position where light is irradiated can be stabilized. Further, the sensor backup roller 8 is biased to the GND potential in order to prevent unnecessary charging that causes transfer failure.

  FIG. 7 is a diagram illustrating the configuration of the optical sensor 18. The optical sensor 18 is a so-called reflection type optical sensor that receives a light emitting element (not shown) that emits light toward the intermediate transfer belt 16 and light reflected by the surface of the intermediate transfer belt 16 and the registration mark. And a light receiving element (not shown). Then, the light emitted from the light emitting element is irradiated to the registration mark on the intermediate transfer belt 16 through the light projection window 182 of the opposing surface 181, while the reflected light from the registration mark is irradiated to the light receiving window of the opposing surface 181. It is guided to the light receiving element by 183. A signal corresponding to the amount of light received by the light receiving element can be output from the optical sensor 18 and color misregistration correction can be performed based on the output signal. Since many methods for correcting color misregistration have been proposed in the past, description thereof is omitted here.

  Returning to FIG. 1, the sheet feeding unit 10 will be described. The sheet feeding unit 10 includes a sheet feeding unit including a sheet feeding cassette 35 in which sheets S are stacked and held, and a pickup roller 36 that feeds the sheets S from the sheet feeding cassette 35 one by one. Also, a registration roller pair 37 that defines the timing of feeding the sheet S to the secondary transfer region TR2, a secondary transfer roller 19 as a secondary transfer unit that is pressed against the driving roller 14 and the intermediate transfer belt 16, and fixing. A unit 12, a paper discharge roller pair 39, and a duplex printing conveyance path 40 are provided.

  The secondary transfer roller 19 is provided so as to be able to come into contact with and separate from the intermediate transfer belt 16 and is driven to come into contact with and separate from a secondary transfer roller drive mechanism (not shown). The fixing unit 12 includes a heating roller 46 that includes a heating element such as a halogen heater and is rotatable, and a pressure roller 45 that presses and biases the heating roller 46. The image secondarily transferred to the sheet S is heat-fixed on the sheet S at a predetermined temperature (for example, 150 ° C. to 180 ° C.) at a nip formed by the heating roller 46 and the pressure roller 45.

  Further, the sheet S thus subjected to the heat fixing process is conveyed to the paper discharge tray 4 provided on the upper surface portion of the housing body 2 via the paper discharge roller pair 39. Further, when images are formed on both sides of the sheet S, when the rear end portion of the sheet S on which the image is formed on one side as described above is conveyed to the reverse position behind the pair of discharge rollers 39. The rotation direction of the discharge roller pair 39 is reversed, whereby the sheet S is conveyed along the duplex printing conveyance path 40. Then, it is put on the conveyance path again before the registration roller pair 37. At this time, the surface of the sheet S to which the image is transferred by contacting the intermediate transfer belt 16 in the secondary transfer region TR2 is transferred first. It is the opposite side of the surface that was made. In this way, images can be formed on both sides of the sheet S.

  In addition, as shown in FIG. 2, the apparatus 1 includes a display unit 54 that is controlled by the CPU 511 of the main controller 51. The display unit 54 is configured by, for example, a liquid crystal display, and in accordance with a control command from the CPU 511, the operation guidance to the user, the progress of the image forming operation, the occurrence of an abnormality in the apparatus, the replacement timing of any unit, and the like A predetermined message for notification is displayed.

  In FIG. 2, reference numeral 513 denotes an image memory provided in the main controller 51 for storing an image given from an external device such as a host computer via the interface 512. Reference numeral 523 denotes a ROM for storing a calculation program executed by the CPU 521, control data for controlling the engine unit EG, and the like. Reference numeral 524 denotes a RAM for temporarily storing calculation results in the CPU 521 and other data. is there.

  As described above, in the first embodiment, when detecting the registration mark position information, the registration mark has a facing surface 181 that faces the surface of the intermediate transfer belt 16, and the registration mark 182 passes through the light projection window 182 of the facing surface 181. A light sensor 18 that emits light toward the light source and detects light incident through the light receiving window 183 of the facing surface 181 is used. The optical sensor 18 is arranged so that the facing surface 181 is located in the vertically lower region of the transfer belt unit 9. Therefore, the toner that has adhered to the surface of the intermediate transfer belt 16 may fall due to gravity and fall on the opposite surface of the optical sensor 18. In such a case, the light emitted from the optical sensor 18 toward the toner image on the surface of the intermediate transfer belt 16 or the light incident on the optical sensor is scattered by the toner that has fallen on the opposing surface 181 to be scattered. The detection accuracy of 18 may decrease.

  However, in the image forming apparatus according to the first embodiment, as shown in FIGS. 5 and 6, the optical sensor 18 is adjacent to the electrode roller 7 in the main scanning direction SD and spaced apart from the electrode roller 7 in the vertically downward direction. Arranged. Accordingly, since the toner is prevented from falling on the optical sensor 18, it is possible to suppress a decrease in detection accuracy of the optical sensor 18 and correct color misregistration. That is, in the image forming apparatus according to the first embodiment, a voltage (+200 [V] of a polarity opposite to that of the negatively charged toner is applied to the conductive layer 162 of the transfer belt 16 by the electrode roller 7 disposed in the vertically lower region of the transfer belt unit 9. ] To transfer the toner image formed on the surface of the photosensitive drum 20 of each of the image forming stations Y, M, C, and K to the intermediate transfer belt 16. Therefore, in the vicinity of the electrode roller 7, an electric field is generated in the direction in which the toner is attracted to the electrode roller 7 side. Therefore, in the first embodiment, since the optical sensor 18 is disposed adjacent to the electrode roller 7 in the main scanning direction SD and spaced apart from the electrode roller 7 in the vertical downward direction, the toner above the optical sensor 18 is gravity-induced. Even when the toner drops from the intermediate transfer belt 16, the toner falls while being attracted to the electrode roller 7 as shown by the broken line in FIG. Therefore, the toner is prevented from falling on the facing surface 181 of the optical sensor 18, and good color misregistration correction is possible.

Second Embodiment
FIG. 8 is a diagram showing a second embodiment of the image forming apparatus according to the present invention. FIG. 9 is a diagram showing an electrical configuration of the second embodiment. In addition, since the basic composition of the apparatus concerning 2nd Embodiment is the same as 1st Embodiment, it attaches | subjects the same and equivalent code | symbol, and abbreviate | omits description. In the second embodiment, the counter electrode 184 is provided on the counter surface 181 of the optical sensor 18, and the counter electrode 184 is connected to the counter electrode bias generator 526 (FIG. 9). A voltage having the same polarity as the negatively charged toner generated by the counter electrode bias generator 526 is applied to the counter electrode 184. Therefore, an electric field that attracts toner from the facing surface 181 of the optical sensor 18 to the electrode roller 7 is surely generated. Therefore, even when the toner above the optical sensor 18 falls from the intermediate transfer belt 16, the toner falls while being more reliably attracted to the electrode roller 7 side. In particular, in the second embodiment, a voltage having the same polarity as that of the toner is applied to the counter electrode 184, and thus a repulsive force is generated between the toner and the counter electrode 184. Therefore, the accumulation of toner on the facing surface 181 of the optical sensor 18 can be more effectively suppressed, and good color misregistration correction can be performed.

<Others>
The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, the counter electrode 184 is provided in the entire range of the counter surface 181 except the light projection window 182 and the light receiving window 183. However, the counter electrode 184 is a part of the counter surface 181 as shown in FIG. It may be provided only in In this case, in order to generate a stronger potential gradient between the counter electrode 184 and the electrode roller 7, it is preferable to dispose the counter electrode 184 closer to the electrode roller 7. This is because, as the potential gradient between the counter electrode 184 and the electrode roller 7 is larger, the toner falling from the intermediate transfer belt 16 is attracted to the electrode roller 7 with a stronger force. This is because the color is suppressed more effectively and good color misregistration correction becomes possible.

  In the second embodiment, a voltage having the same polarity as that of the negatively charged toner is applied to the counter electrode 184 of the optical sensor 18 by the counter electrode bias generation unit 526. However, the GND potential is applied to the counter electrode 184. You may do it. Even in such a configuration, an electric field that attracts toner from the facing surface 181 of the optical sensor 18 to the electrode roller 7 as compared with a configuration in which the opposing electrode 184 is not provided on the facing surface 181 of the optical sensor 18. It occurs more reliably. Therefore, the accumulation of toner on the optical sensor 18 is suppressed, and good color misregistration correction is possible.

  Further, when the GND potential is applied to the electrode roller 7 in this way, the following configuration may be made by utilizing the fact that the sensor backup roller 8 is biased to the GND potential. That is, the GND potential may be applied to the electrode roller 7 by electrically short-circuiting the electrode roller 7 to the sensor backup roller 8. In such a configuration, it is not necessary to provide the counter electrode bias generator 526, and the apparatus configuration can be simplified.

  In the above embodiment, the intermediate transfer belt 16 is a belt composed of three layers of the base layer 161, the vapor deposition layer 162, and the coating layer 164. However, the structure of the intermediate transfer belt 16 is not limited to this. That is, you may use the belt of the structure of 4 or more layers which has a layer further in addition to the said 3 layers.

  In the above embodiment, the belt electrode 165 is provided in the voltage application region of the intermediate transfer belt 16, but the conductive layer 162 is directly exposed without providing the belt electrode 165 as shown in FIG. 11, for example. The portion may be a voltage application region. However, from the viewpoint of preventing corrosion of the conductive layer 162, a configuration in which the belt electrode 165 is provided is more preferable.

  In the above embodiment, the developing method using the negatively charged toner is used. However, the polarity of the charged toner is not limited to this, and the present invention can be applied to the case where a positively charged toner is used.

  In the above embodiment, the image forming stations Y, M, C, and K are arranged in this order from the upstream side to the downstream side in the belt conveyance direction D16. However, the arrangement order of the image forming stations is limited to this. It is not a thing.

1 is a diagram illustrating a basic configuration of an image forming apparatus according to the present invention. 1 is a block diagram showing an electrical configuration of an image forming apparatus according to a first embodiment. FIG. 3 is a schematic diagram illustrating a structure of an intermediate transfer belt in the first embodiment. The schematic diagram which shows the arrangement | positioning position of an electrode roller. The schematic diagram which shows the arrangement | positioning position of an optical sensor. The schematic diagram which shows the arrangement | positioning position of an optical sensor. The schematic diagram which shows the structure of the optical sensor in 1st Embodiment. The schematic diagram which shows the structure of the optical sensor in 2nd Embodiment. FIG. 6 is a diagram illustrating an electrical configuration of an image forming apparatus according to a second embodiment. The schematic diagram which shows the structure of the optical sensor in other embodiment of this invention. FIG. 6 is a schematic diagram showing a structure of an intermediate transfer belt in another embodiment of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 7 ... Electrode roller, 8 ... Sensor backup roller, 9 ... Transfer belt unit, 14 ... Drive roller (conveyance means), 151, 152, 153 ... Driven roller (conveyance means), 16 ... Intermediate transfer belt (Transfer belt), 161 ... base layer, 162 ... conductive layer, 165 ... belt electrode (voltage application region), 18 ... optical sensor, 181 ... facing surface, 182 ... light projection window, 183 ... light receiving window, 20 ... photoconductor Drum (latent image carrier), 21 ... elastic member, 525 ... primary transfer bias generator, 526 ... counter electrode bias generator, D16 ... (intermediate transfer belt) moving direction, Y, M, C, K ... image Forming station, SD ... Main scanning direction

Claims (6)

A transfer belt unit comprising a transfer belt having a plurality of layers including a conductive layer and a transport means for rotating and transporting the transfer belt in a predetermined transport direction, and a latent image provided in each of the transfer belt units arranged along the transport direction of the transfer belt A plurality of image forming stations that form toner images of different colors by developing a latent image carried on the surface of the image carrier with toner having a predetermined polarity; and a conductive layer of the transfer belt having a polarity opposite to that of the toner. An electrode roller for transferring and superimposing toner images of different colors formed on the latent image carrier of each of the plurality of image forming stations to the transfer belt surface by applying a voltage, and facing the transfer belt surface Formed on the surface of the transfer belt in order to correct color misregistration between the plurality of image forming stations via the opposing surface. An optical sensor that emits light to the toner image and detects light incident through the opposing surface, and the optical sensor has an opposing surface located in a vertically lower region of the transfer belt unit. In the arranged image forming apparatus,
The transfer belt has a belt-like shape with a predetermined width in the main scanning direction substantially orthogonal to the transport direction and has a voltage application region electrically short-circuited with the conductive layer at one end of the transfer belt. ,
The electrode roller is disposed in a vertically lower region of the transfer belt unit and contacts the voltage application region to apply a voltage to the conductive layer of the transfer belt,
The image forming apparatus, wherein the photosensor is adjacent to the electrode roller in the main scanning direction and is spaced apart from the electrode roller in a vertically downward direction.   The transfer belt has a structure of at least three layers having the conductive layer between a base layer provided on the innermost periphery of the transfer belt and a coating layer provided on the outermost periphery of the transfer belt, The image forming apparatus according to claim 1, wherein the voltage application region is formed by removing a layer on an outer peripheral side from the conductive layer in the strip shape and exposing the conductive layer in the strip shape.   The transfer belt has a structure of at least three layers having the conductive layer between a base layer provided on the innermost periphery of the transfer belt and a coating layer provided on the outermost periphery of the transfer belt, 2. The image forming apparatus according to claim 1, wherein the voltage application region is formed by removing a layer on the outer peripheral side from the conductive layer in the strip shape and providing a belt electrode in the strip portion at the removed portion.   The image forming apparatus according to claim 1, wherein a counter electrode is provided on the counter surface of the photosensor, and the counter electrode is biased to a GND potential.   4. The image forming apparatus according to claim 1, wherein a counter electrode is provided on the counter surface of the photosensor, and the counter electrode is biased to a potential having the same polarity as the toner. 5. The image forming apparatus according to claim 4, further comprising a sensor backup roller facing the opposite surface of the optical sensor via the transfer belt and contacting the back surface of the transfer belt and biased to a GND potential. ,
An image forming apparatus biased to a GND potential by electrically short-circuiting the counter electrode to the sensor backup roller.

Images