JP4015107B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to at least one image carrier on which a toner image is formed, a light-transmitting transfer belt disposed opposite to the image carrier and stretched over a plurality of support rollers, and a plurality of supports. A reflection-type optical sensor disposed opposite to a part of the support roller via a transfer belt, and a detection mark transferred from the image carrier to the transfer belt is detected by the optical sensor; The present invention relates to an image forming apparatus.

  Various types of apparatuses have been proposed and put to practical use for the above-mentioned type of image forming apparatus configured as an electronic copying machine, a printer, a facsimile, or a complex machine of these. For example, a direct transfer type image forming apparatus that directly transfers a toner image formed on an image carrier onto a recording medium carried on a transfer belt (see, for example, Patent Documents 1 and 2), an image carrier 2. Description of the Related Art Conventionally, an intermediate transfer type image forming apparatus that transfers a toner image formed on a body onto a transfer belt and transfers the toner image onto a recording medium is well known.

  In any type of image forming apparatus, a detection mark is formed on the image carrier, the detection mark is transferred to a transfer belt, the transferred detection mark is detected by an optical sensor, and based on detection data obtained thereby. Thus, the image forming apparatus is adjusted or controlled to obtain a high-quality image. For example, in an image forming apparatus having a plurality of image carriers on which toner images of different colors are formed, detection marks formed on the respective image carriers are sequentially transferred onto a transfer belt, and this is used as an optical sensor. Thus, the amount of color misregistration is detected and the color misregistration is corrected based on this. In that case, in the image forming apparatus described at the beginning, the optical sensor is arranged to face the support roller, and the support roller is used as a facing member of the optical sensor, so that the configuration of the image forming apparatus is simplified. be able to. That is, the light emitted from the light emitting element of the optical sensor and transmitted through the transfer belt is reflected by the opposing member made of the support roller, and the reflected light is incident on the light receiving element of the optical sensor. Therefore, it is not necessary to provide an independent opposing member, and the configuration of the image forming apparatus can be simplified and the cost thereof can be reduced.

  Incidentally, the transfer belt is driven across a plurality of support rollers, and foreign matters such as paper dust and toner enter between these support rollers and the transfer belt, and the foreign matters are transferred to the transfer belt. If it adheres to the back surface and the back surface is soiled with foreign matter, the optical sensor cannot correctly detect the detection mark on the transfer belt, and the detection accuracy decreases.

  Therefore, the diameter of each support roller peripheral surface facing the transfer belt region where the detection mark is formed is set to be small, and the image formation is configured such that the peripheral surface of the support roller does not contact the transfer belt region where the detection mark is formed. An apparatus has been proposed (see Patent Document 1). According to this type of image forming apparatus, occurrence of erroneous detection of detection patterns can be effectively suppressed.

Japanese Patent Laid-Open No. 10-104898 JP 2003-76111 A

  When the above configuration is adopted in the image forming apparatus of the type described at the beginning, the light emitted from the optical sensor and transmitted through the transfer belt reaches the bottom surface of the annular groove portion of the support roller having a reduced diameter, and is reflected here. Then, the light again passes through the transfer belt and enters the light receiving element of the optical sensor. At this time, if the depth of the annular groove portion is deep, light that goes out of the transfer belt toward the bottom surface of the annular groove portion of the support roller diffuses in the space between the transfer belt and the bottom surface. For this reason, the fault which the reading accuracy of the detection mark by an optical sensor falls is unavoidable.

  An object of the present invention is to provide an image forming apparatus of the type described at the beginning, which eliminates the above-mentioned conventional drawbacks.

  In order to achieve the above object, according to the present invention, in the image forming apparatus of the type described at the beginning, a transfer belt area where the detection mark is formed is a mark formation area, and other transfer belt areas are non-mark formation areas. In the support roller in which the optical sensor is arranged to face, the diameter of the peripheral surface facing the mark forming region and the diameter of the peripheral surface facing the non-mark forming region are set equal, and the optical sensor An image forming apparatus characterized in that the diameter of the peripheral surface facing the mark formation region is set smaller than the diameter of the peripheral surface facing the mark non-formation region in the support rollers that are not arranged to face each other. Propose.

  According to the present invention, the occurrence of contamination on the back surface of the transfer belt can be suppressed, and the diffusion of the light emitted from the light emitting element of the optical sensor and transmitted through the transfer belt can be suppressed, thereby increasing the detection accuracy of the detection mark. be able to.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, and conventional defects will be clarified more specifically with reference to the drawings.

  FIG. 1 is a schematic view showing an example of a direct transfer type image forming apparatus, and this image forming apparatus is configured as a printer. The image forming apparatus shown here includes a plurality of image carriers 3Y, 3M, 3Y, 3BK arranged in a main body 1 and a transfer belt 4 comprising an endless belt arranged to face these image carriers. have. Each of the image carriers 3Y to 3BK is constituted by a drum-shaped photoconductor, and a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image are formed on the surface of each image carrier. The transfer belt 4 is stretched around a plurality of support rollers 15, 16, 17, 18 and driven to run in the direction of arrow A. The transfer belt 4 is made of a light transmissive material.

  Since the operation of forming a toner image on each of the image carriers 3Y, 3M, 3C, and 3BK is substantially the same, only the configuration of forming a toner image on the image carrier 3Y will be described. The image carrier 3Y is rotated clockwise in FIG. 1, and at this time, the surface of the image carrier 3Y is uniformly charged to a predetermined polarity by the charging device 7. Next, the charged surface is irradiated with a light-modulated laser beam L emitted from the laser writing unit 8. As a result, an electrostatic latent image is formed on the image carrier 3Y, and the electrostatic latent image is visualized as a yellow toner image by the developing device 9.

  On the other hand, a paper feeding device 5 is disposed in the lower part of the image forming apparatus main body 1, and this paper feeding device 5 is pressed against a paper feeding cassette 14 for storing the recording medium P and the uppermost recording medium. A paper feed roller 12 that rotates and feeds the uppermost recording medium in the direction of arrow B is provided. The recording medium P sent out from the paper feeding device 5 is fed between the image carrier 3Y and the transfer belt 4 at a predetermined timing by the registration roller pair 13, and is carried on the transfer belt 4. Be transported. A transfer device 10 is disposed at a position almost opposite to the image carrier 3Y across the transfer belt 4, and the yellow toner image on the image carrier 3Y is transferred onto the recording medium P by the action of the transfer device 10. The The transfer residual toner that is not transferred to the recording medium P and remains on the image carrier 3Y is removed by the cleaning device 11.

  In exactly the same manner, a magenta toner image, a cyan toner image, and a black toner image are respectively formed on the image carriers 3M, 3C, and 3BK shown in FIG. 1, and these toner images are transferred with a yellow toner image. The images are sequentially transferred onto the recording medium P. The recording medium P carrying the four-color superimposed toner image in this way passes through the fixing device 2, and at this time, the superimposed toner image is fixed on the recording medium P by the action of heat and pressure. The recording medium that has passed through the fixing device 2 is discharged onto the paper discharge unit 6 as indicated by an arrow C. Further, toner, paper dust, and the like adhering to the surface of the transfer belt 4 are removed by the cleaning device 19.

  In the image forming apparatus configured as described above, for various purposes, a detection mark made of a toner image is formed on the transfer belt, and the detection mark is arranged so as to be opposed to the transfer belt 4. It is detected by the sensor 20.

  FIG. 2 is a schematic perspective view showing the detection mark M formed on the transfer belt 4 and the optical sensor 20 that detects the detection mark M. Here, two optical sensors 20 are provided, but the number thereof is set to an appropriate number including one.

  In the same manner as the image forming operation described above, detection marks of each color are formed on the image carriers 3Y to 3BK that are driven to rotate clockwise in FIG. 1, and the detection marks are driven in the direction of the arrow A. The image is transferred onto the transfer belt 4 by the transfer device, and a detection mark M as shown in FIG. 2 is formed on the transfer belt. These detection marks M are detected by the optical sensor 20, and based on the obtained detection data, the color misregistration amounts of the superimposed toner images transferred from the image carriers 3Y to 3BK onto the recording medium P are detected. Is corrected.

  As can be seen from FIG. 1, the optical sensor 20 is located downstream of the transfer position where the toner image is transferred from the image carriers 3Y to 3BK to the transfer belt 4, and on the downstream side of the transfer belt surface movement direction. The detection mark M that is disposed upstream of the cleaning device 19 to be moved in the moving direction of the transfer belt surface and has passed through the optical sensor 20 is removed from the surface of the transfer belt 4 by the cleaning device 19.

  Further, the optical sensor 20 is disposed to face the support roller 16 with the transfer belt 4 interposed therebetween. For this reason, a dedicated opposing member for the optical sensor 20 is unnecessary, and the configuration of the image forming apparatus can be simplified. If necessary, an optical sensor can be provided to face the other support rollers 15, 17, 18. In short, a reflection type optical sensor is disposed opposite to a part of the plurality of support rollers via a transfer belt, and a detection mark transferred from the image carrier to the transfer belt is displayed on the optical sensor. It is detected by.

  Here, as described above, foreign matters such as toner and paper dust are sandwiched between the transfer belt 4 and the support rollers 15, 16, 17, and 18 that support the transfer belt. If it adheres to the back surface of the transfer belt 4, the detection mark M cannot be detected correctly, and erroneous detection occurs.

  Therefore, the following configuration is adopted in the image forming apparatus of this example.

  In FIG. 2, the entire circumference of the transfer belt 4 on which the detection mark M is formed is indicated by a two-dot chain line. This area is referred to as a mark formation area MA, and other areas of the transfer belt 4 are not formed with marks. It will be referred to as region MB. FIG. 3 is a partial cross-sectional view showing the relative positional relationship between the support roller 16, the optical sensor 20, and the transfer belt 4. FIG. 4 shows the relative position of the support rollers 15, 17, and 18 and the transfer belt 4. It is a fragmentary sectional view. As can be seen from FIGS. 2 to 4, the diameters d1 and d2 of the peripheral surfaces of the support rollers 15 to 18 facing the mark formation area MA of the transfer belt 4 are respectively opposite to the mark non-formation areas MB of the transfer belt 4. It is set smaller than the diameter D of the peripheral surface of the support rollers 15 to 18. The portions of the support rollers 15 to 18 facing the mark forming area MA are formed as annular grooves. For this reason, the back surface of the mark formation area MA does not contact the peripheral surfaces of the support rollers 15 to 18. This makes it difficult for foreign matters such as toner and paper dust to adhere to the back surface, and prevents erroneous detection of the detection mark M. The portions of the support rollers 15 to 18 in which the diameters d1 and d2 are set to be small are referred to as small-diameter portions, and the small-diameter portions are denoted by symbols SD1 and SD2 to identify them.

  As shown in FIG. 3, when the light LI emitted from the light emitting element of the optical sensor 20 hits the detection mark M on the transfer belt 4, most of the light is absorbed, whereas the light LI other than the detection mark M is absorbed. The light LI that hits the surface of the transfer belt 4 passes through the transfer belt 4 as shown by a one-dot chain line in FIG. 3 and is reflected by the bottom surface 21 of the small diameter portion SD1 of the support roller 16, and the reflected light is again transferred to the transfer belt. 4 enters the light receiving element of the optical sensor 20.

  In this way, the detection mark M can be detected, but if the small diameter portion SD1 annular groove is deep, the light LI that passes through the transfer belt 4 and travels toward the bottom surface 21 will diffuse. Therefore, the detection mark M cannot be detected correctly, and the detection accuracy may be reduced.

  Therefore, in the image forming apparatus of this example, as can be seen from FIG. 3 and FIG. 4, the diameter d1 of the small diameter portion SD1 of the support roller 16 on which the optical sensor 20 is disposed is not disposed opposite to the optical sensor 20. The diameter is set larger than the diameter d2 of the small diameter part SD2 of the support rollers 15, 17, and 18. For example, the depth W2 of the small diameter portion SD2 of the support rollers 15, 17, and 18 that are not disposed opposite to the optical sensor 20 is set to 0.5 mm, whereas the small diameter of the support roller 16 that is disposed opposite to the optical sensor 20 is set. The depth W1 of the part SD1 is set to 0.1 to 0.2 mm.

  According to the above configuration, since the depth W1 of the small diameter portion SD1 of the support roller 16 is shallow, it is possible to suppress the diffusion of the light emitted from the light emitting element of the optical sensor 20 and transmitted through the transfer belt 4, thereby The detection accuracy of the detection mark M can be increased. However, since the depth W1 of the small-diameter portion SD1 is shallow, foreign matter is more likely to adhere to the back surface of the mark forming area MA compared to the case where the depth W1 is deep, but the support rollers 15, 17,. Since the depth W2 of the 18 small-diameter portion SD2 is formed deep, it is possible to prevent foreign matter from adhering to the mark forming area MA when viewed from the entire transfer belt 4, and this is caused by contamination of the transfer belt 4. It is possible to effectively suppress the erroneous detection of the detection mark to be performed.

  Further, in the support rollers 15, 17, and 18 where the optical sensor 20 is not disposed oppositely, as shown in FIG. 4, the diameter d 2 of the peripheral surface facing the mark forming area MA is opposed to the mark non-forming area MB. As shown in FIG. 5, in the support roller 16 that is set smaller than the diameter D of the peripheral surface and the optical sensor 20 is oppositely disposed, as shown in FIG. These diameters can also be set so that the diameter D of the peripheral surface facing the formation region MB becomes equal, that is, d1 = D. The back surface of the mark forming area MA of the transfer belt 4 is brought into contact with the peripheral surface of the support roller 16 without forming a small diameter portion on the support roller 16 facing the optical sensor 20. Thereby, it can prevent more effectively that the light which radiate | emitted the optical sensor 20, and permeate | transmitted the transfer belt 4 is spread | diffused. In addition, since the small-diameter portion SD2 is formed on the support rollers 15, 17, and 18 that are not opposed to the optical sensor 20, it is possible to suppress the problem that foreign matter adheres to the back surface of the mark formation area MA of the transfer belt 4. . In this way, the detection accuracy of the detection mark can be increased.

  FIG. 6 shows an example of an intermediate transfer type image forming apparatus. In the image forming apparatus shown here, similarly to the image forming apparatus shown in FIG. 1, toner images of different colors are formed on the plurality of image carriers 3Y, 3M, 3C, 3BK. Each of the toner images is transferred so as to be superimposed on the transfer belt 4 which is disposed to face the image carriers 3Y to 3BK and which is stretched over the support rollers 15, 16 and 17 and driven in the direction of arrow A. The superimposed toner image on the transfer belt 4 is fed from the sheet feeding device 5 by a transfer roller 22 which is an example of a secondary transfer device, and is fed between the transfer belt 4 and the transfer roller 22 by a registration roller pair 13. Transferred to the recording medium P. The intermediate transfer belt after the toner image is transferred is cleaned by a belt cleaning device 19. The recording medium to which the toner image has been transferred passes through the fixing device 2, and at this time, the toner image is fixed to the recording medium P. The recording medium P that has passed through the fixing device 2 is discharged to the paper discharge unit 6 at the top of the image forming apparatus main body 1. In FIG. 6, an optical sensor 20 is provided opposite to the support roller 16, and the detection marks transferred from the image carriers 3 </ b> Y to 3 </ b> BK to the transfer belt are detected by the optical sensor. Each of the configurations described above with reference to FIGS. 2 to 5 can also be adopted in such an image forming apparatus.

  Furthermore, the present invention provides an image forming apparatus that forms a single color toner image on one image carrier and transfers the toner image onto a recording medium carried on a transfer belt to obtain a recorded image. Toner images of different colors are sequentially formed on the image carrier, and the toner images are transferred onto the recording medium carried on the transfer belt and transferred, or transferred onto the transfer belt and transferred to each other. The present invention can also be applied to an image forming apparatus that forms a recorded image by transferring a toner image to a recording medium.

  As described above, the present invention provides at least one image carrier on which a toner image is formed, and a light-transmitting transfer belt that is disposed so as to face the image carrier and is stretched over a plurality of support rollers. And a reflection type optical sensor arranged to face a part of the plurality of support rollers via the transfer belt, and the toner image formed on the image carrier is carried on the transfer belt. The toner image formed on the image carrier is transferred to the transfer belt, and the toner image on the transfer belt is recorded. The image forming apparatus is configured to obtain a recorded image by being transferred to a medium, and can be applied to an image forming apparatus that detects a detection mark transferred from an image carrier to a transfer belt by an optical sensor.

1 is a schematic sectional view illustrating an example of a direct transfer type image forming apparatus. FIG. 2 is a perspective view showing a transfer belt of the image forming apparatus shown in FIG. 1 and detection marks formed on the surface thereof. FIG. 6 is a partial cross-sectional view illustrating a relative positional relationship between an optical sensor, a support roller on which the optical sensor is disposed to be opposed, and a transfer belt. It is a fragmentary sectional view which shows the positional relationship of the support roller which is not opposingly arranged of an optical sensor, and a transfer belt. It is a fragmentary sectional view which shows the other example of relative positional relationship of an optical sensor, the support roller by which the optical sensor is opposingly arranged, and a transfer belt. 1 is a schematic cross-sectional view illustrating an example of an intermediate transfer type image forming apparatus.

Explanation of symbols

3Y, 3M, 3C, 3BK Image carrier 4 Transfer belt 15, 16, 17, 18 Support roller 20 Optical sensor d1, d2, D diameter M Detection mark MA Mark formation area MB Mark non-formation area SD1, SD2 Small diameter portion

Claims (1)

At least one image carrier on which a toner image is formed; a light-transmitting transfer belt disposed opposite to the image carrier; In an image forming apparatus, comprising: a reflection type optical sensor arranged to face a part of a support roller via a transfer belt, and detecting a detection mark transferred from the image carrier to the transfer belt by the optical sensor ,
When the area of the transfer belt on which the detection mark is formed is a mark formation area and the area of the other transfer belt is a mark non-formation area, the support roller on which the photosensor is disposed is arranged in the mark formation area. In the supporting roller in which the diameter of the facing circumferential surface and the diameter of the circumferential surface facing the non-mark forming area are set to be equal, and the optical sensor is not arranged to face, the diameter of the circumferential surface facing the mark forming area is An image forming apparatus, wherein the image forming apparatus is set smaller than a diameter of a peripheral surface facing the mark non-formation region.

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