JP2009265234A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, having no adverse influence on rotation of an intermediate transfer body, and preventing local adhesion of toner external additive to the surface of the intermediate transfer body so that the occurrence of image unevenness is prevented to perform image formation with high quality. <P>SOLUTION: This image forming apparatus 1 includes: a cleaning device 50 for the intermediate transfer belt 8 provided with a fur brush 52 rotating in contact with an intermediate transfer belt 8 and also removing deposit on the surface thereof, a cleaning roller 53 for removing deposit of the fur brush 52, and a moving mechanism 100 for changing the distance of the cleaning roller 53 to the fur brush 52; and a density detecting sensor 14 for detecting the surface density of the intermediate transfer belt 8. The distance of the cleaning roller 53 to the fur brush 52 is changed by the moving mechanism 100 corresponding to the degree of the surface density of the intermediate transfer belt 8 detected using the density detecting sensor 14. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus typified by a copying machine or a printer, and more particularly to an image forming apparatus that transfers a toner image onto a sheet using an intermediate transfer member.

  In an electrophotographic image forming apparatus such as a copying machine or a printer, a photosensitive drum is widely used as an image carrier. A general image forming operation using the photosensitive drum is as follows. The surface of the photosensitive drum is uniformly charged with a predetermined potential by a charging device, and the potential is partially attenuated by irradiating the LED light of the exposure device, etc., to form an electrostatic latent image of the original image. Is done. The electrostatic latent image is developed with a developing device, whereby a toner image is formed on the surface of the photosensitive drum. This toner image is transferred to the sheet when the sheet is inserted into a transfer region formed by bringing the photosensitive drum and the transfer member into contact with each other or close to each other.

  The image forming apparatus includes a type in which a toner image is directly transferred from a photosensitive drum, which is an image carrier, onto a sheet, and a toner image is once carried on an intermediate transfer body and then transferred from the intermediate transfer body to a sheet. There is also. The intermediate transfer member is often found in an image forming apparatus for color printing such as a so-called tandem type image forming apparatus in which image forming units corresponding to a plurality of colors of toner are arranged in a line. Examples of such an image forming apparatus can be found in Patent Documents 1 and 2.

  In the image forming apparatus as described above, after a toner image is transferred to a sheet, a small amount of toner may remain on the surface of the intermediate transfer member without being transferred to the sheet. The residual toner adhering to the surface of the intermediate transfer member becomes a hindrance to the next new image formation, and therefore needs to be cleaned.

  In the image forming apparatuses described in Patent Documents 1 and 2, residual toner on the surface of the intermediate transfer member is cleaned by a cleaning device (cleaning unit, cleaning roller) for the intermediate transfer member. This intermediate transfer member cleaning device is usually rubbed or scraped using a brush, roller, or blade, and an electric force that applies an electrostatic force by applying a bias. Clean the surface of the intermediate transfer member.

Some of the cleaning devices as described above use a fur brush to clean the residual toner. An example of such a cleaning device can be seen in US Pat. The cleaning device described in Patent Document 3 cleans the residual toner on the surface of the photosensitive drum. In order to stabilize the residual toner removal performance by the fur brush, the fur brush is connected to the photosensitive drum and the collection roller. The separation / contact mechanism is provided to perform raising control.
Japanese Patent Laying-Open No. 2003-241472 (page 4, FIG. 1) JP 2007-94000 (page 4, FIG. 1) Japanese Patent Laid-Open No. 4-296922 (page 2-3, FIG. 1)

  The toner particles remaining on the surface of the intermediate transfer member have a relatively weak physical force applied to the surface of the intermediate transfer member and are charged, and can be easily removed by a cleaning device. However, external additives such as titanium oxide and silica that are supplied together with the toner particles may pierce the surface of the intermediate transfer member, have a strong physical force to adhere to the surface of the intermediate transfer member, and are almost charged. It may be difficult to remove with a cleaning device.

  When the same image pattern is continuously printed or when images are continuously formed at the same location in the circumferential direction of the intermediate transfer member, uneven adhesion of the external additive to the surface of the intermediate transfer member is uneven. Arise. When unevenness of the external additive adheres to the surface of the intermediate transfer member, the unevenness of the image at intermediate density occurs. This is because the friction coefficient of the surface of the intermediate transfer member where the external additive is attached is lower than the friction coefficient of the portion where the external additive is not attached, and the transfer performance is improved in transferring the toner image on the surface of the intermediate transfer member to the paper. However, this is because the image density is high. Therefore, with respect to the adhesion of the external additive to the surface of the intermediate transfer member, the toner image is uniformly adhered while suppressing uneven adhesion, thereby reducing the coefficient of friction of the entire surface of the intermediate transfer member with respect to the toner image and transferring the toner image to the paper. It is desirable to improve.

  In this regard, like the cleaning device described in Patent Document 3, by providing a fur brush separation / contact mechanism with the intermediate transfer member, the residual toner removal performance by the fur brush on the intermediate transfer member surface is controlled, It is conceivable that the external additive is uniformly attached to the surface of the intermediate transfer member. However, in this cleaning device, since the contact pressure between the fur brush and the intermediate transfer member changes, there is a concern that the rotational torque of the intermediate transfer member may fluctuate. If the rotational torque of the intermediate transfer member fluctuates, the moving speed of the surface of the intermediate transfer member fluctuates, which may cause problems such as color misregistration and density unevenness.

  The present invention has been made in view of the above points, and in an image forming apparatus having an intermediate transfer member that once carries a toner image, the toner on the surface of the intermediate transfer member without adversely affecting the rotation of the intermediate transfer member. By preventing local adhesion of the external additive, it is possible to improve the transfer performance of the toner image from the intermediate transfer member to the paper and prevent the occurrence of image unevenness, thereby achieving high-quality image formation. An object of the present invention is to provide an image forming apparatus that can perform the above-described process.

  In order to solve the above-mentioned problems, the present invention provides a fur brush that removes deposits on the surface of an image forming apparatus having an intermediate transfer member that temporarily holds a toner image while rotating in contact with the intermediate transfer member. An intermediate transfer member cleaning device provided with a cleaning roller for removing deposits on the fur brush, a moving mechanism capable of changing the distance of the cleaning roller from the fur brush, and the surface concentration of the intermediate transfer member. And a distance between the cleaning roller and the fur brush is changed by a moving mechanism in accordance with the density of the surface density of the intermediate transfer member detected by using the density detection sensor. It was.

  Further, in the image forming apparatus having the above-described configuration, the density detection sensor is common to a sensor that performs deviation detection and density detection of the toner image once transferred to the surface of the intermediate transfer member.

  In the image forming apparatus having the above-described configuration, the intermediate transfer member has an elastic layer on the surface thereof.

  In addition, the image forming apparatus having the above configuration includes an image carrier that is a photosensitive member made of amorphous silicon.

  According to the configuration of the present invention, in the image forming apparatus including the intermediate transfer member that once carries the toner image, the fur brush that removes the adhering material on the surface while rotating in contact with the intermediate transfer member, and the fur Intermediate transfer member cleaning device provided with a cleaning roller for removing brush deposits and a moving mechanism capable of changing the distance between the cleaning roller and the fur brush, and a concentration for detecting the surface concentration of the intermediate transfer member In addition to the detection sensor, the distance between the cleaning roller and the fur brush is changed by the moving mechanism in accordance with the density of the surface density of the intermediate transfer member detected using the density detection sensor. By controlling the cleaning performance of the fur brush with the cleaning roller, It is possible to control the distillation toner removal performance. As a result, it is possible to prevent local adhesion, that is, uneven adhesion of the toner external additive to the surface of the intermediate transfer member without changing the rotational torque of the intermediate transfer member, and to uniformly adhere to the entire surface. It is possible. Thereby, it is possible to reduce the friction coefficient with respect to the toner image on the entire surface of the intermediate transfer member. Therefore, it is possible to improve the transfer performance of the toner image from the intermediate transfer member to the paper without adversely affecting the rotation of the intermediate transfer member, thereby preventing the occurrence of image unevenness and performing high-quality image formation. It is possible to obtain an image forming apparatus capable of performing the above.

  In addition, since the density detection sensor is common to a sensor that performs deviation detection and density detection of the toner image once transferred to the surface of the intermediate transfer body, in order to detect the surface density of the intermediate transfer body, There is no need to provide a separate sensor. Thereby, reduction of a number of parts and reduction of parts installation space can be aimed at. Therefore, it is possible to improve the performance of transferring the toner image from the intermediate transfer member to the paper while reducing the cost and saving the space, thereby preventing the occurrence of image unevenness and performing high-quality image formation. Is possible.

  In addition, the intermediate transfer member having an elastic layer on the surface covers the adverse effects caused by the characteristics of the paper with the elastic force even when the thickness of the paper and the unevenness of the surface differ depending on the paper type. It is possible to improve the transfer performance regardless of the paper type. On the other hand, however, there is a concern that the external additive of the toner is likely to adhere to the surface, and uneven adhesion tends to occur. Therefore, by combining an intermediate transfer member having an elastic layer on the surface with the image forming apparatus of the present invention, the external additive can be uniformly attached to the entire surface, so that the toner from the intermediate transfer member to the paper It is possible to improve image transfer performance and prevent image unevenness.

  In addition, a photoconductor composed of amorphous silicon is widely used in image forming apparatuses because it has high hardness and excellent wear resistance and has a very long life. On the other hand, however, there is also a problem that the coefficient of friction of the surface becomes higher when the usage time as the image carrier elapses. Therefore, by combining a photoconductor composed of amorphous silicon with the image forming apparatus of the present invention, the toner supply for reducing the friction coefficient on the surface of the intermediate transfer member reduces the friction coefficient on the surface of the image carrier. In addition, since the transfer performance of the toner image from the image carrier to the intermediate transfer member is also improved, it is possible to maintain higher quality image formation.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  First, an image output operation of an image forming apparatus according to an embodiment of the present invention will be described while explaining an outline of the structure with reference to FIGS. 1 and 2. FIG. 1 is a schematic vertical sectional front view of the image forming apparatus, and FIG. 2 is a partially enlarged vertical sectional view around the intermediate transfer belt shown in FIG. This image forming apparatus is of a color printing type in which a toner image is transferred onto a sheet using an intermediate transfer belt.

  As shown in FIG. 1, a paper feed cassette 3 is disposed below the inside of the main body 2 of the image forming apparatus 1. The paper feed cassette 3 stores and accommodates paper P such as cut paper before printing. The sheets P are separated and sent one by one toward the upper left of the sheet cassette 3 in FIG. The paper feed cassette 3 can be pulled out horizontally from the front side of the main body 2.

  A first paper transport unit 4 is provided inside the main body 2 and to the left of the paper feed cassette 3. The first paper transport unit 4 is formed substantially vertically along the left side surface of the main body 2. The first paper transport unit 4 receives the paper P sent out from the paper feed cassette 3 and transports the paper P vertically upward along the left side surface of the main body 2 to the secondary transfer unit 40.

  A manual paper feed unit 5 is provided above the paper feed cassette 3 at a location on the right side which is the side opposite to the left side of the main body 2 where the first paper transport unit 4 is formed. Yes. In the manual sheet feeder 5, paper P of a size that is not contained in the paper cassette 3, thick paper, and OHP sheets that are to be fed one by one are placed.

  A second paper transport unit 6 is provided on the left side of the manual paper feed unit 5. The second paper transport unit 6 is located immediately above the paper feed cassette 3, extends substantially horizontally from the manual paper feed unit 5 to the first paper transport unit 4, and joins the first paper transport unit 4. Then, the second paper transport unit 6 receives the paper P or the like sent from the manual paper feed unit 5 and transports it to the first paper transport unit 4 substantially horizontally.

  On the other hand, the image forming apparatus 1 receives document image data from an external computer (not shown). The information of the image data is sent to a laser irradiation unit 7 that is an exposure unit disposed above the second paper transport unit 6. The laser irradiation unit 7 irradiates the image forming unit 20 with laser light L controlled based on the image data.

  As shown in FIGS. 1 and 2, a total of four image forming units 20 are used above the laser irradiation unit 7, and an intermediate transfer member is used in the form of an endless belt above each image forming unit 20. An intermediate transfer belt 8 is provided. The intermediate transfer belt 8 is supported by being wound around a plurality of rollers, and is rotated clockwise in FIG. 2 by a driving device (not shown).

  As shown in FIGS. 1 and 2, the four image forming units 20 are arranged in a row from the upstream side to the downstream side in the rotational direction along the rotational direction of the intermediate transfer belt 8 in a so-called tandem system. is there. The four image forming units 20 are, in order from the upstream side, a magenta image forming unit 20M, a cyan image forming unit 20C, a yellow image forming unit 20Y, and a black image forming unit 20B. These image forming units 20 are replenished with a developer (toner) by a developer supply container and a conveying unit (not shown) corresponding to each color. In the following description, the identification symbols “M”, “C”, “Y”, and “B” are omitted unless particularly limited.

  In each image forming unit 20, an electrostatic latent image of a document image is formed by the laser light L irradiated by the laser irradiation unit 7 serving as an exposure unit, and the toner image is developed from the electrostatic latent image. The toner image is primarily transferred to the surface of the intermediate transfer belt 8 by the primary transfer unit 30 provided above each image forming unit 20. As the intermediate transfer belt 8 rotates, the toner image of each image forming unit 20 is transferred to the intermediate transfer belt 8 at a predetermined timing, so that the surface of the intermediate transfer belt 8 is magenta, cyan, yellow, or black. A color toner image is formed by superimposing the color toner images.

  A secondary transfer unit 40 including a secondary transfer roller 41 is disposed at a position where the intermediate transfer belt 8 is suspended on the sheet conveyance path. The color toner image once carried on the surface of the intermediate transfer belt 8 is formed by the intermediate transfer belt 8 and the secondary transfer roller 41 being in pressure contact with the paper P sent in synchronization by the first paper transport unit 4. Is transferred at the secondary transfer nip portion.

  After the secondary transfer, deposits such as toner remaining on the surface of the intermediate transfer belt 8 are cleaned for the intermediate transfer belt 8 provided upstream of the intermediate transfer belt 8 in the rotation direction of the magenta image forming unit 20M. It is cleaned and collected by the device 50. The configuration of the intermediate transfer belt cleaning device 50 will be described in detail later.

  A fixing unit 10 is provided above the secondary transfer unit 40. The paper P carrying the unfixed toner image in the secondary transfer unit 40 is sent to the fixing unit 10 where the toner image is heated and pressed by the heat roller and the pressure roller to be fixed.

  A branch portion 11 is provided above the fixing portion 10. The sheet P discharged from the fixing unit 10 is discharged from the branching unit 11 to the sheet discharging unit 12 provided on the upper part of the image forming apparatus 1 when double-sided printing is not performed.

  The discharge port portion from which the paper P is discharged from the branch portion 11 toward the paper discharge portion 12 functions as the switchback portion 13. When performing duplex printing, the switchback unit 13 switches the transport direction of the paper P discharged from the fixing unit 10. Then, the sheet P is sent downward through the branching unit 11, the left side of the fixing unit 10, and the left side of the secondary transfer unit 40, and again passes through the first sheet transport unit 4 to the secondary transfer unit 40. Sent.

  Next, a detailed configuration around the image forming unit 20 and the intermediate transfer belt 8 of the image forming apparatus 1 will be described with reference to FIG. 3 in addition to FIG. FIG. 3 is a partially enlarged vertical sectional view showing the periphery of the image forming unit. Since the four color image forming units 20 have the same structure, the identification symbols “M”, “C”, “Y”, and “B” are omitted as described above.

  As shown in FIG. 3, the image forming unit 20 includes a photosensitive drum 21 that is an image carrier at the center thereof. In the vicinity of the photosensitive drum 21, a charging device 60, a developing device 70, a charge removal device 80, and a drum cleaning device 90 are arranged in this order along the rotation direction. The primary transfer unit 30 is provided between the developing device 70 and the charge removal device 80 along the rotation direction of the photosensitive drum 21.

  The photoconductor drum 21 extends in the paper width direction perpendicular to the paper conveyance direction in the image forming apparatus 1, that is, the depth direction of the paper surface in FIG. The photosensitive drum 21 is an inorganic photosensitive drum in which an amorphous silicon photosensitive layer, which is an inorganic photoconductive material, is provided on the outer side of a conductive roller-shaped substrate made of aluminum or the like by vacuum deposition or the like, and has a diameter of 30 mm. It is. The photosensitive drum 21 is rotated by a driving device (not shown) so that the peripheral speed thereof is substantially the same as the paper conveyance speed (150 mm / s). Note that the four image forming apparatuses 20 shown in FIG. 2 are rotated by individual drive devices each including a DC motor and a gear.

  The charging device 60 includes a charging roller 62 in contact with the photosensitive drum 21 inside the housing 61. The charging roller 62 is pressed against the photosensitive drum 21 with a predetermined pressure, and rotates according to the rotation of the photosensitive drum 21. By this charging roller 62, the surface of the photosensitive drum 21 is uniformly charged with a predetermined polarity and potential. The charging potential at this time is normally plus 350V. A cleaning brush 63 is provided in the housing 61 at a position separating the charging roller 62 from the photosensitive drum 21, and the surface of the charging roller 62 is cleaned by the cleaning brush 63.

  The developing device 70 includes a developing roller 72 and a supply screw 73 inside the housing 71. The developing roller 72 is provided in the vicinity of the photosensitive drum 21 with a developing method being contact or non-contact. A bias having the same polarity as the charging polarity of the photosensitive drum 21 is applied to the developing roller 72. The developing roller 72 charges the toner, which is a developer, and moves it to the electrostatic latent image on the surface of the photosensitive drum 21 to develop the electrostatic latent image.

  The developing device 70 uses a two-component toner obtained by mixing a magnetic carrier and a non-magnetic toner as a developer, but may be of a type using a magnetic or non-magnetic one-component toner. Absent. Further, in order to clean the surface of the photosensitive drum 21 by polishing, a small amount of powder such as titanium oxide or silica is mixed in the toner as an external additive. The toner is accommodated in a developer supply container (not shown), conveyed to a location of the developing device 70 by a conveying means (not shown), and replenished inside the housing 71 by a supply screw 73.

  The primary transfer unit 30 is provided with a primary transfer roller 31 that comes into contact with the photosensitive drum 21 via the intermediate transfer belt 8. The primary transfer roller 31 is a roller having a diameter of 20 mm, in which an EPDM (ethylene propylene diene rubber) foam having a thickness of 6 mm is provided on a metal shaft having a diameter of 8 mm. The primary transfer roller 31 does not have a driving device, and rotates according to the rotation of the intermediate transfer belt 8 by contacting the intermediate transfer belt 8. The primary transfer roller 31 is applied with a primary transfer bias of minus 15 μA, which has a polarity different from the charging polarity of the photosensitive drum 21 and the toner, as necessary.

  As shown in FIG. 2, the intermediate transfer belt 8 is wound around and supported by a plurality of rollers. The intermediate transfer belt 8 is an elastic endless belt provided by laminating an elastic layer on the surface of a substrate. A PVDF (polyvinylidene fluoride) resin having a thickness of 0.1 mm is used as a base material of the intermediate transfer belt 8, and an NBR rubber (nitrile rubber) having a thickness of 0.1 mm is provided as an elastic layer on the surface thereof. Further, the elastic layer is coated with PTFE (polytetrafluoroethylene) having a thickness of 10 μm.

  Among the rollers that support the intermediate transfer belt 8, as shown in FIG. 2, a roller provided at a location facing the secondary transfer roller 41 across the intermediate transfer belt 8 is driven in the vicinity of the secondary transfer portion 40. This is a roller 8a. The drive roller 8a is connected to a stepping motor (not shown) that is a drive motor, and rotates the intermediate transfer belt 8 at a speed of 150 mm / s. The driving roller 8a is a roller having a diameter of 30 mm, in which EPDM (ethylene propylene diene rubber) is provided with a thickness of 1.5 mm on a metal shaft having a diameter of 27 mm.

  On the other hand, the secondary transfer roller 41 is a roller having a diameter of 24 mm in which a metal shaft having a diameter of 10 mm is provided with an EPDM (ethylene propylene diene rubber) foam having a thickness of 7 mm. The secondary transfer roller 41 is rotated by obtaining power through a gear from a drive motor connected to a drive roller 8 a that rotates the intermediate transfer belt 8. The secondary transfer roller 41 is applied with a secondary transfer bias of −30 μA, which has a polarity different from that of the photosensitive drum 21 or the toner, as necessary.

  As shown in FIG. 3, the static eliminator 80 of the image forming unit 20 is disposed on the downstream side of the primary transfer unit 30 along the rotation direction of the photosensitive drum 21. The static eliminating device 80 includes an LED (light emitting diode) 81 and a reflecting plate 82. The LED 81 is attached to the upper surface of the housing 91 of the cleaning device 90. Instead of the LED 81, an EL (electroluminescence) light source, a fluorescent lamp, or the like can be used. The reflection plate 82 is provided above the LED 81 so as to cover the LED 81. The neutralizing device 80 irradiates the photosensitive drum 21 with the neutralizing light from the LED 81 to remove the charged charge on the surface thereof, and prepares for the charging process in the next image forming operation.

  The cleaning device 90 for the photosensitive drum 21 is disposed further downstream of the primary transfer unit 30 and the charge removal device 80 along the rotation direction of the photosensitive drum 21. The drum cleaning device 90 includes a cleaning roller 92, a cleaning blade 93, a toner receiving member 94, a transport paddle 95, and a toner discharge screw 96 inside the housing 91. The cleaning roller 92 and the cleaning blade 93 are in pressure contact with the photosensitive drum 21, and remove adhering matters such as toner remaining on the surface of the photosensitive drum 21 for cleaning. The toner removed from the surface of the photosensitive drum 21 is temporarily stored inside the toner receiving member 94, and the overflowed toner is sent to the toner discharge screw 96 through the transport paddle 95. Thus, the waste toner is discharged by the toner discharge screw 96 to a waste toner collection container (not shown) outside the cleaning device 90.

  Here, in the image forming apparatus 1 having the image forming unit 20 and the intermediate transfer belt 8 as described above, a density detection sensor 14 is provided in the vicinity of the secondary transfer unit 40 as shown in FIG. ing. The density detection sensor 14 is disposed downstream of the black image forming unit 20B in the rotation direction of the intermediate transfer belt 8 and below the intermediate transfer belt 8 with the secondary transfer unit 40. Yes. Further, a plurality of density detection sensors 14 are provided along the rotational axis direction of the intermediate transfer belt 8, that is, in the sheet width direction, for example, three.

  The concentration detection sensor 14 is configured by a non-contact optical sensor including a light emitting unit and a light receiving unit (not shown). The light emitting part of the density detection sensor 14 emits light at a predetermined angle toward the surface of the upper intermediate transfer belt 8 and the light receiving part receives the reflected light reflected by the surface of the intermediate transfer belt 8. The density detection sensor 14 can determine the density of the toner image by outputting, as a voltage value, the level of reflected light on the surface of the intermediate transfer belt 8 that has received light.

  In order to perform high-quality image formation, the image forming apparatus 1 checks image density and color misregistration periodically or at an arbitrary timing. At this time, a correction toner pattern is formed on the surface of the intermediate transfer belt 8 using each image forming unit 20, and the density detection sensor 14 executes density detection and deviation detection of the toner pattern. If there is a difference from the reference in the toner pattern detected by the density detection sensor 14, the density and color misregistration are corrected using preset parameters.

  The density detection sensor 14 that executes density detection and deviation detection of the toner image once transferred to the surface of the intermediate transfer belt 8 in this way can also detect the surface density of the intermediate transfer belt 8 itself.

  Next, a detailed configuration of the cleaning device 50 for the intermediate transfer belt 8 will be described with reference to FIGS. 4 and 5 in addition to FIG. 4 is a partially enlarged vertical sectional view showing the periphery of the intermediate transfer belt cleaning device, and FIG. 5 is a partially enlarged vertical sectional view showing the periphery of the intermediate transfer belt cleaning device similar to FIG. Is shown.

  As described above, the cleaning device 50 for the intermediate transfer belt 8 is disposed on the upstream side in the rotation direction of the magenta image forming unit 20M with respect to the intermediate transfer belt 8 (see FIG. 2). The intermediate transfer belt cleaning device 50 includes a fur brush 52, a cleaning roller 53, a cleaning blade 54, a moving mechanism 100 for the cleaning roller 53, and a discharge screw 55 inside the housing 51.

  The fur brush 52 is provided at a location facing the driven roller 8b that supports the intermediate transfer belt 8 around which the intermediate transfer belt 8 is wound. The fur brush 52 is a rotating brush in which an animal fur or synthetic fiber is formed in a cylindrical shape around a core bar having a diameter of 8 mm so that a diameter at a hair end portion is 17 mm. They have the same length in the rotational axis direction, and are arranged so that their hair tips are pressed against the surface of the intermediate transfer belt 8. Further, the fur brush 52 is rotated by a motor (not shown) in such a direction that the hair tip portion moves in a direction different from the surface of the intermediate transfer belt 8. The fur brush 52 serves to collect deposits such as residual toner from the surface of the intermediate transfer belt 8.

  The cleaning roller 53 is disposed at a location separating the fur brush 52 from the intermediate transfer belt 8. The cleaning roller 53 is configured in such a manner that rubber is provided around the mandrel, and has substantially the same length in the rotation axis direction as the fur brush 52. The cleaning roller 53 is arranged in pressure contact with the fur brush 52 so as to bite in from the surface constituted by the fur tips of the fur brush 52 toward the axis of the fur brush 52. The cleaning roller 53 is rotated by a motor (not shown) in such a direction that the surface at the contact point with the fur brush 52 moves in the same direction as the surface of the fur brush 52. The cleaning roller 53 plays a role of collecting deposits such as residual toner from the surface of the fur brush 52.

  The cleaning blade 54 is disposed at a position separating the cleaning roller 53 from the fur brush 52. The cleaning blade 54 is provided to be pressed against the cleaning roller 53 with a predetermined force. The cleaning blade 54 is a rectangular parallelepiped member made of polyurethane rubber, such as a plate extending in the rotation axis direction of the cleaning roller 53, and has substantially the same axial length as the cleaning roller 53. The cleaning blade 54 plays a role of cleaning so as to scrape off the adhering matter such as toner remaining on the surface of the cleaning roller 53.

  The cleaning roller 53 and the cleaning blade 54 are attached to the moving mechanism 100. The moving mechanism 100 includes a support member 101, a motor 102, a pinion 103, and a rack 104.

  The support member 101 supports the cleaning roller 53 and the cleaning blade 54. The support member 101 can be slid in the up and down direction as viewed from the front by moving the cleaning roller 53 closer to or away from the fur brush 52 by a slide unit (not shown).

  The motor 102 is disposed outside the housing 51 of the intermediate transfer belt cleaning device 50. A pinion 103 is fixed to the tip of the shaft portion of the motor 102. A rack 104 is fixed to the support member 101 so as to follow the direction in which the support member 101 slides. The pinion 103 and the rack 104 are engaged with each other to form a rack and pinion mechanism.

  4 and 5, the moving mechanism 100 can slide the support member 101 with the rack and pinion mechanism by driving the motor 102, and the cleaning roller 53 is moved to the fur brush 52. The distance between the cleaning roller 53 and the fur brush 52 can be changed.

  The discharge screw 55 is provided below the cleaning roller 53 and the cleaning blade 54 in the housing 51. The discharge screw 55 extends from the inside of the housing 51 to a waste toner collection container (not shown) provided outside the intermediate transfer belt cleaning device 50. The discharge screw 55 serves to discharge waste toner and the like in the housing 51 removed from the surface of the intermediate transfer belt 8 to the outside of the housing 51, that is, to a waste toner collection container.

  Subsequently, a method of controlling the intermediate transfer belt cleaning device 50 with respect to the surface density of the intermediate transfer belt 8 itself detected by the density detection sensor 14 will be described with reference to FIGS. 6 and 7 in addition to FIGS. explain. FIG. 6 is a table showing the relationship of the amount of cleaning roller biting into the fur brush with respect to the surface density of the intermediate transfer belt, and FIG. 7 is a table showing changes in the occurrence of image unevenness depending on whether or not the intermediate transfer belt cleaning device is controlled.

  Here, it is known that the new intermediate transfer belt 8 has a higher output voltage and higher surface density than the used one, compared to the used one. In this regard, since the NBR rubber (nitrile rubber) is provided as an elastic layer on the surface of the intermediate transfer belt 8, it is relatively black at an initial stage close to a new product.

  On the other hand, the used intermediate transfer belt 8 which has been used for a long time since the initial stage is a new toner, and since the external additive adheres and remains due to the primary transfer of the toner image, the phenomenon of so-called whitening progresses and the surface becomes It becomes relatively whitish. As a result, the used intermediate transfer belt 8 has a lower surface density than that of a new one, so that the output voltage of the density detection sensor 14 is lowered.

  Further, the new intermediate transfer belt 8 usually has a small and stable fluctuation in the output voltage of the density detection sensor 14, is stable, and the density of the entire surface is substantially uniform. As a result, since the friction coefficient with respect to the toner image is uniform over the entire surface of the intermediate transfer belt 8, image unevenness can be prevented in the secondary transfer of the toner image from the intermediate transfer belt 8 to the paper P. However, when the intermediate transfer belt 8 is nearly new, the friction coefficient with respect to the toner image on the entire surface thereof is almost uniform, but the friction coefficient itself is relatively high, so that it can be said that more suitable secondary transfer performance can be obtained. It is desirable to further reduce the friction coefficient. Therefore, the adhesion of the external additive to the surface of the intermediate transfer belt 8 should be promoted to reduce the surface concentration.

  On the other hand, the used intermediate transfer belt 8 generally has an external additive adhering and remaining due to the primary transfer of the toner image, and the friction coefficient with respect to the toner image as a whole is relatively low. The voltage fluctuation is large and unstable, and the concentration on the entire surface may be uneven and non-uniform. That is, there is a possibility that uneven adhesion of the external additive occurs on the surface of the intermediate transfer belt 8. This increases the possibility of image unevenness during secondary transfer of the toner image from the intermediate transfer belt 8 to the paper P.

  In order to deal with such uneven adhesion of the external additive on the surface of the intermediate transfer belt 8, the intermediate transfer belt cleaning is performed in accordance with the surface density of the intermediate transfer belt 8 detected by using the density detection sensor 14. The apparatus 50 is controlled.

  As shown in FIG. 6, when the surface density of the intermediate transfer belt 8 itself detected using the density detection sensor 14 is high, that is, when the external additive adheres little to the surface of the intermediate transfer belt 8, the intermediate transfer belt cleaning device is used. 50 drives the moving mechanism 100 of the cleaning roller 53 to change the distance between the cleaning roller 53 and the fur brush 52 so that the amount of the cleaning roller 53 biting into the fur brush 52 becomes 0.5 mm (FIG. 5).

  As described above, when the amount of the cleaning roller 53 biting into the fur brush 52 is relatively small, the cleaning performance of the surface of the fur brush 52 by the cleaning roller 53 is deteriorated. Accordingly, since a relatively large amount of toner and its external additive remain on the surface of the fur brush 52, adhesion of the external additive from the fur brush 52 to the surface of the intermediate transfer belt 8 is promoted, and the surface concentration is reduced. Can do. As a result, the friction coefficient with respect to the toner image on the entire surface of the intermediate transfer belt 8 can be reduced, and more suitable secondary transfer performance can be obtained.

  On the other hand, as shown in FIG. 6, as the surface density of the intermediate transfer belt 8 itself detected by using the density detection sensor 14 decreases, that is, as the amount of external additives attached to the surface of the intermediate transfer belt 8 increases, the intermediate transfer The belt cleaning device 50 drives the moving mechanism 100 of the cleaning roller 53 so that the amount of biting of the cleaning roller 53 into the fur brush 52 becomes 0.8 mm or 1.0 mm. (See FIG. 4).

  Thus, when the cleaning roller 53 bites into the fur brush 52 is relatively large, the cleaning performance of the surface of the fur brush 52 by the cleaning roller 53 is improved. Accordingly, the cleaning performance of the surface of the intermediate transfer belt 8 by the fur brush 52 is also improved, so that it is possible to prevent unnecessary toner and external additives from remaining on the surface of the intermediate transfer belt 8. As a result, it is possible to maintain a state where the friction coefficient with respect to the toner image on the entire surface of the intermediate transfer belt 8 is lowered and obtain a more suitable secondary transfer performance, and it is possible to perform a clearer image formation. Become.

  FIG. 7 shows a result of executing the control of the intermediate transfer belt cleaning device 50 with respect to the surface density of the intermediate transfer belt 8 itself detected by the density detection sensor 14 as described above. Here, it was verified whether image unevenness occurred after printing 1000 sheets and 5000 sheets when the control of the intermediate transfer belt cleaning device 50 was not executed and when it was executed. For verification of image unevenness, a halftone toner patch of 50 mm in the rotation axis direction of the intermediate transfer belt 8 and 150 mm in the circumferential direction (rotation direction) is formed on the paper P, and whether or not the unevenness occurs is visually observed. confirmed. In FIG. 7, the occurrence of image unevenness is evaluated by the fact that the occurrence cannot be confirmed (◯), the occurrence can be confirmed slightly (Δ), and the occurrence is remarkable (×).

  According to FIG. 7, when the control of the intermediate transfer belt cleaning device 50 is not executed, it can be seen that the occurrence of image unevenness becomes remarkable as the printing proceeds to 1000 sheets and 5000 sheets. On the other hand, when the control of the intermediate transfer belt cleaning device 50 is executed, it can be seen that image unevenness does not occur even if printing is advanced to 1000 sheets and 5000 sheets. Therefore, the control of the intermediate transfer belt cleaning device 50 effectively works to prevent uneven adhesion of the external additive on the surface of the intermediate transfer belt 8.

  As described above, in the image forming apparatus 1 provided with the intermediate transfer belt 8 that is an intermediate transfer member that temporarily holds the toner image, the fur brush that removes the deposits on the surface while rotating in contact with the intermediate transfer belt 8. 52, a cleaning roller 53 that removes deposits on the fur brush 52, and a cleaning mechanism 50 for the intermediate transfer belt 8 provided with a moving mechanism 100 that can change the distance of the cleaning roller 53 from the fur brush 52. And a density detection sensor 14 for detecting the surface density of the intermediate transfer belt 8, and in accordance with the surface density of the intermediate transfer belt 8 detected using the density detection sensor 14, the moving mechanism 100 Since the distance between the cleaning roller 53 and the fur brush 52 is changed, the cleaning roller 53 has a cleaning line for the fur brush 52. 53 by by controlling the cleaning performance, it is possible to control the residual toner removing performance by the fur brush 52 to the intermediate transfer belt 8 surfaces. As a result, it is possible to prevent local adhesion, that is, uneven adhesion of the toner external additive to the surface of the intermediate transfer belt 8 without changing the rotational torque of the intermediate transfer belt 8, and evenly over the entire surface. It is possible to adhere. As a result, the friction coefficient of the entire surface of the intermediate transfer belt 8 with respect to the toner image can be reduced. Therefore, the transfer performance of the toner image from the intermediate transfer belt 8 to the paper P can be improved without adversely affecting the rotation of the intermediate transfer belt 8, and the occurrence of image unevenness can be prevented, and high quality image formation can be achieved. The image forming apparatus 1 capable of performing the above can be obtained.

  The density detection sensor 14 is common to a sensor that detects deviation and density detection of the toner image once transferred to the surface of the intermediate transfer belt 8, and therefore separately detects the surface density of the intermediate transfer belt 8. There is no need to provide a sensor. Thereby, reduction of a number of parts and reduction of parts installation space can be aimed at. Accordingly, the toner image transfer performance from the intermediate transfer belt 8 to the paper P can be improved while reducing cost and space saving, and the occurrence of image unevenness can be prevented, and high-quality image formation can be performed. It becomes possible to do.

  Furthermore, the intermediate transfer belt having an elastic layer on the surface covers the adverse effects caused by the characteristics of these papers, even if the paper thickness and surface irregularities differ depending on the paper type. It is possible to improve the transfer performance regardless of the paper type. On the other hand, however, there is a concern that the external additive of the toner is likely to adhere to the surface, and uneven adhesion tends to occur. Therefore, by combining the intermediate transfer belt 8 having an elastic layer on the surface with the image forming apparatus 1 of the present invention, the external additive can be uniformly attached to the entire surface. It becomes possible to prevent the occurrence of image unevenness by improving the transfer performance of the toner image to P.

  In addition, a photoconductor composed of amorphous silicon is widely used in image forming apparatuses because it has high hardness and excellent wear resistance and has a very long life. On the other hand, however, there is also a problem that the coefficient of friction of the surface becomes higher when the usage time as the image carrier elapses. Therefore, a photosensitive drum 21 that is an image carrier is supplied by combining a photosensitive member made of amorphous silicon with the image forming apparatus 1 of the present invention to supply toner for reducing the friction coefficient of the surface of the intermediate transfer belt 8. The surface friction coefficient can also be reduced, and the transfer performance of the toner image from the photosensitive drum 21 to the intermediate transfer belt 8 is improved, so that it is possible to maintain higher quality image formation.

  Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the invention.

  For example, in the embodiment of the present invention, the intermediate transfer member is the intermediate transfer belt 8 in the form of an endless belt, but the type of the intermediate transfer member is not limited to this, and a drum-shaped intermediate member is used. It may be a transfer body.

  Further, although the three density detection sensors 14 are arranged along the rotation axis direction (paper width direction) of the intermediate transfer belt 8, the number and the arrangement locations of the density detection sensors 14 are not limited to this. Alternatively, two or more sensors of four or more may be arranged at various locations.

  The present invention can be used in all image forming apparatuses in which a toner image is once transferred to an intermediate transfer member and then secondarily transferred from the intermediate transfer member to a sheet.

1 is a schematic vertical sectional front view of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a partially enlarged view of a vertical cross section around an intermediate transfer belt shown in FIG. 1. FIG. 3 is an enlarged view of a vertical cross section around the image forming unit shown in FIG. 2. FIG. 3 is a partially enlarged vertical sectional view showing the periphery of an intermediate transfer belt cleaning device shown in FIG. 2. FIG. 5 is a partially enlarged vertical sectional view showing the periphery of the intermediate transfer belt cleaning device similar to FIG. 4 and shows a state where the cleaning roller is moved. 6 is a table showing the relationship of the amount of cleaning roller biting into the fur brush with respect to the surface density of the intermediate transfer belt. 6 is a table showing changes in the occurrence of image unevenness depending on whether or not the intermediate transfer belt cleaning device is controlled.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Main body 8 Intermediate transfer belt (intermediate transfer body)
14 Density Detection Sensor 20 Image Forming Unit 21 Photosensitive Drum (Image Carrier)
30 Primary transfer unit 31 Primary transfer roller 40 Secondary transfer unit 41 Secondary transfer roller 50 Cleaning device for intermediate transfer belt (cleaning device)
52 Fur brush 53 Cleaning roller 54 Cleaning blade 100 Moving mechanism 101 Support member 102 Motor 103 Pinion 104 Rack

Claims (4)

In an image forming apparatus including an intermediate transfer member that once carries a toner image,
The fur brush that removes deposits on the surface while rotating in contact with the intermediate transfer member, the cleaning roller that removes deposits on the fur brush, and the distance between the cleaning brush and the fur brush can be changed. An intermediate transfer body cleaning device provided with a moving mechanism, and a density detection sensor for detecting the surface density of the intermediate transfer body, and the density of the surface density of the intermediate transfer body detected using the density detection sensor. Correspondingly, the distance between the cleaning roller and the fur brush is changed by a moving mechanism.   The image forming apparatus according to claim 1, wherein the density detection sensor is common to a sensor that performs deviation detection and density detection of a toner image once transferred to the surface of the intermediate transfer member.   The image forming apparatus according to claim 1, wherein the intermediate transfer member has an elastic layer on a surface thereof.   The image forming apparatus according to claim 1, further comprising an image carrier that is a photosensitive member made of amorphous silicon.

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