JP5459607B2 - Transfer device and image forming apparatus - Google Patents

Description

  The present invention transfers a toner image carried on each of a plurality of image carriers to an endless belt member or a recording member held on the surface thereof, and the belt member is subjected to a specific image carrier by a change in its stretching posture. The present invention relates to an image forming apparatus that contacts and separates from a body.

  As this type of image forming apparatus, the one described in Patent Document 1 is known. This image forming apparatus includes four photoconductors that individually carry yellow (Y), magenta (M), cyan (C), and black (K) toner images as a plurality of image carriers. An intermediate transfer belt, which is an endless belt member, is brought into contact with these four photoconductors to form primary transfer nips for Y, M, C, and K. In the color mode for forming a full-color image, Y, M, C, and K toner images developed on the surfaces of the four photoconductors are superposed and transferred onto the surface of the intermediate transfer belt at their primary transfer nips. Have gained. In the monochrome mode for forming a monochrome image, the tension of the intermediate transfer belt is changed to separate the intermediate transfer belt from three of the four photoconductors for M, C, and K. In this state, the K toner image formed on the photoreceptor of the K photoreceptor is primarily transferred onto the surface of the intermediate transfer belt to obtain a monochrome image. In such a configuration, in the monochrome mode, the M, C, and K photoconductors that do not contribute to image formation are separated from the intermediate transfer belt, thereby suppressing unnecessary power consumption and wear of the photoconductor and the belt. it can.

  On the other hand, the image density and relative position of the reference toner image of each color transferred to the surface of the intermediate transfer belt for the purpose of correcting the excess or deficiency of the density of each color toner image or the positional deviation, An image forming apparatus that detects an image by an image detection sensor is known. For the toner image detection sensor, in order to avoid the deterioration of detection accuracy due to the waving of the belt, the toner image detection sensor is arranged so as to face the wrapping area of the tension roller where the undulation hardly occurs in the entire area in the circumferential direction of the intermediate transfer belt. It is common to install. However, in the image forming apparatus described in Patent Document 1, when the wrapping area for the tension roller, which is a tension roller, is to be opposed to the toner image detection sensor, the belt is greatly waved at the sensor facing position. It will be easier to hit. Specifically, the tension roller is urged toward the belt by a spring or the like inside the belt loop so as to apply a constant tension to the belt. As in the image forming apparatus described in Patent Document 1, in the case where the belt is brought into and out of contact with the M, C, and K photoconductors by changing the belt stretching posture, along with the contact and separation operation. The belt tension changes. Then, the tension roller greatly moves in the biasing direction by the spring or the opposite direction in accordance with the change in tension, and the tension of the belt member is restored to the original state. In such a configuration in which the tension roller is largely moved, for example, the toner image detection sensor is wound around the tension roller in the intermediate transfer belt while the intermediate transfer belt is in contact with the M, C, and K photoconductors. Assume that Then, in the color mode in which the image forming operation is performed in that state, the above-described wrapping region that hardly causes undulation can be set as a region to be detected by the toner image detection sensor. However, in the monochrome mode in which the intermediate transfer belt is separated from the M, C, and K photoconductors, the tension roller is largely moved in accordance with the separation so that the above-described running region is a region facing the toner image detection sensor. I will remove it. As a result, the belt extension region that greatly undulates as the vehicle travels becomes the region to be detected by the toner image detection sensor, and the detection accuracy deteriorates. In recent years, where the number of tension rollers arranged in the belt loop tends to be reduced as much as possible with the aim of reducing the size of the apparatus, a layout in which the toner image detection sensor is arranged near the tension roller has to be adopted. No situation is likely to occur. For this reason, it is difficult to accurately detect the image density and relative position of the reference toner image.

  As an image forming apparatus capable of avoiding deterioration in the detection accuracy of the reference toner image due to the movement of the tension roller, the one described in Patent Document 2 is known. In this image forming apparatus, the toner image detection sensor is fixed to a movable holding body that moves in the urging direction together with the tension roller while rotatably holding the rotation shaft of the tension roller. In such a configuration, even if the tension roller is largely moved in accordance with the change in the belt stretching posture, the toner image detection sensor is also moved in the same direction by the same amount. As a result, regardless of the belt stretching posture, the belt wrapping region with respect to the tension roller can be opposed to the toner image detection sensor.

  However, in this image forming apparatus, it is necessary to secure an empty space allowing movement of the toner image detection sensor in addition to an empty space allowing movement of the tension roller and the belt as an empty space in the apparatus. There is a problem of preventing the miniaturization of the.

  The present invention has been made in view of the above background, and an object thereof is to provide the following image forming apparatus. That is. This is an image forming apparatus capable of suppressing deterioration in detection accuracy of the toner image detecting means due to the undulation of the belt member without moving the toner image detecting means together with a tension applying member such as a tension roller.

In order to achieve the above object, a first aspect of the present invention provides a plurality of image carriers that carry toner images on their surfaces and a plurality of toner images that are respectively carried on the surfaces of the image carriers. A transfer means for transferring to the front surface of an endless belt member that moves endlessly while being stretched by the member, or a recording member held on the front surface; and a transfer means disposed in a loop of the belt member. A tension-applying member that applies a tension to the belt member by urging the inner member of the loop in contact with the back surface of the belt, and applying tension to the belt member; and a circumference of the front surface of the belt member A toner image detecting means for detecting a toner image transferred to the front surface, the toner image detecting means being disposed near a tensioning area for the tension applying member among all the areas in the direction; and the belt member in the circumferential direction. What is the wrapping area? Made with to change the predetermined stretched position of the first region in an image forming apparatus and a moving means for contacting and separating the first region in one or more specific image-bearing member, said moving means As the inner member of the loop disposed in the loop of the belt member is moved between a predetermined position and a position shifted to the outside of the loop, the stretching posture of the first region is changed. As the contact / separation means changes the stretching posture of the first region, the loop outer member disposed outside the loop of the belt member is placed at a predetermined position and more than this. The belt member is contacted with the belt member by changing a tension posture of a predetermined second region different from the hanging region of the belt member as the belt member is moved to a position shifted to the inside of the loop. Of the tension posture by the movement of the separating means Into the back tension generation means for generating a tension change in the opposite direction is provided to the tension change due, and the lubricant applying means for applying a lubricant on the front surface of the belt member, and said loop outer member The belt portion before entering the contact position is disposed at a position where the coating process is performed .
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, an interlocking mechanism for interlocking the reverse tension generating unit with the contacting / separating unit is provided.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the belt member tension change caused by the change in the tension posture due to the operation of the contact / separation means is changed in the reverse direction tension change. The amount of change in the tension posture of the first region due to the operation of the contact / separation means and the amount of change in the tension posture of the second region due to the operation of the reverse tension generating means are set as values that can be offset. It is characterized by.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the specific image carrier is an image carrier that carries a toner image having a color different from black. The first area is contacted / separated by contact / separation means, and an image carrier carrying black toner is brought into contact with the belt member regardless of the operation of the contact / separation means. It is what.
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the toner image detecting means is disposed at a position facing the wrapping area. .
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the first region is defined by the contact / separation unit with respect to two or more image carriers as the specific image carrier. The two or more image carriers are arranged in a straight line so that the contact portions with the first region in the two or more image carriers are positioned on the same virtual straight line. The contact portion with the belt member in the image carrier to be brought into contact with the belt member regardless of the operation of the contact / separation means is located at a position shifted from the virtual straight line inside the loop of the belt member. To do.
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the same drive source is shared by the contacting / separating means and the reverse tension generating means. .
Also, the invention of claim 8, in any of the image forming apparatus according to claim 1 to 7, as the loop outer member, is characterized in that with the driven rotatable loop outer roller.
Also, the invention of claim 9, in any one of the image forming apparatus according to claim 1 to 8, as the lubricant applying unit, with use of which lubricate the belt member by the brush member, said loop The external material is disposed in the vicinity of the lubricant applying means.

  In these inventions, the deterioration of the detection accuracy of the toner image detection means due to the undulation of the belt member can be suppressed without moving the toner image detection means together with the tension applying member for the reason described below. That is, when the contacting / separating means changes the stretching posture of the first region of the belt member to bring the first region into contact with or separates from the specific image carrier, the belt member is changed along with the change of the stretching posture. Try to weaken or strengthen the tension. Then, as it is, the tension applying member moves toward the outer side or the inner side of the belt loop so as to keep the tension of the belt member constant, so that the toner image detecting unit approaches or moves away. Therefore, in the present invention, as the contacting / separating means changes the tension posture of the first region of the belt member, the reverse tension generating means changes the tension posture of the second region of the belt member, and the belt member On the other hand, a tension change in a direction opposite to the tension change accompanying the change in the tension posture of the first region is generated. Thereby, the amount of movement of the tension applying member when the contact / separation means operates is reduced by reducing the change in tension of the belt member when the contact / separation means operates. In such a configuration, even when the contact / separation unit is operated, the tension applying member is allowed to stay in the vicinity of the toner image detecting unit, and the belt wrapping region or the vicinity thereof with respect to the tension applying member can be opposed to the toner image detecting unit. It becomes possible. Therefore, it is possible to suppress the deterioration of the detection accuracy of the toner image detecting means due to the undulation of the belt member without moving the toner image detecting means together with the tension applying member.

FIG. 2 is a main part configuration diagram showing a main part of the printer according to the embodiment. The schematic diagram for demonstrating shape factor SF-1. The schematic diagram for demonstrating shape factor SF-2. FIG. 3 is a main part configuration diagram illustrating a state in a printer in a monochrome mode in which only a K toner image is formed. FIG. 6 is an enlarged configuration diagram showing each color photoconductor and a part of an intermediate transfer belt in a conventional printer. FIG. 2 is an enlarged configuration diagram illustrating each color process unit and a part of a transfer unit of the printer according to the embodiment in an enlarged manner. FIG. 3 is a configuration diagram showing a state of contact / separation means and reverse tension generation means in the printer when the intermediate transfer belt is in contact with Y, M, and C photoconductors. FIG. 3 is a configuration diagram showing states of contact / separation means and reverse tension generation means in the printer when the intermediate transfer belt is separated from Y, M, and C photoconductors. FIG. 10 is a main configuration diagram illustrating a modification of the printer according to the embodiment. FIG. 2 is a main part configuration diagram illustrating the printer in a state in which an intermediate transfer belt is separated from Y, M, and C photoconductors.

Hereinafter, a color printer (hereinafter simply referred to as a printer) that forms an image by an electrophotographic method will be described as an image forming apparatus to which the present invention is applied.
First, a basic configuration of the printer according to the embodiment will be described. FIG. 1 is a main part configuration diagram showing a main part of the printer according to the embodiment. This printer includes four process units 2Y, 2M, 2C, and 2K for forming yellow (Y), magenta (M), cyan (C), and black (K) toner images. Further, a registration roller pair 45, a transfer unit 20, a fixing device 50, an optical writing unit (not shown), a paper feed cassette, and the like are also provided.

  An optical writing unit (not shown) is disposed above the four process units 2Y, 2M, 2C, and 2K, and includes a laser diode, a polygon mirror, various lenses, and the like. Then, the photoconductors 3Y, 3M, 3C, and 3K of the process units 2Y, 2M, 2C, and 3K are optically scanned with scanning light emitted based on image information sent from an external personal computer or the like. Specifically, the photoconductors 3Y, 3M, 3C, and 3K of the process units 2Y, 2M, 2C, and 2K are rotated in the clockwise direction in the drawing by driving means (not shown). The optical writing unit performs optical scanning processing by irradiating the driving photosensitive members 3Y, 3M, 3C, and 3K while deflecting scanning light in the direction of the rotation axis. Thereby, electrostatic latent images based on Y, M, C, and K image information are formed on the photoreceptors 3Y, 3M, 3C, and 3K.

  The process units 2K, Y, M, and C for the respective colors support the photosensitive member as an image carrier and various devices disposed around it on a common support as a single unit. It becomes removable with respect to. The configuration is the same except that the colors of the toners used are different. The process unit 2Y for Y will be described as an example. This is not only the photoreceptor 3Y but also the charging device 4Y for uniformly charging the surface of the photoreceptor 3Y, and the electrostatic latent image formed on the surface as a Y toner image. A developing device 5Y for developing, a drum cleaning device 6Y for cleaning residual toner on the surface, and the like are included. The described scanning light is applied to the region immediately after being uniformly charged by the charging device 4Y, out of the entire region in the circumferential direction of the photoreceptor 3Y. This printer employs a so-called tandem configuration in which the four process units 2Y, 2M, 2C, and 2K having such a configuration are arranged along the endless movement direction with respect to an intermediate transfer belt 21 described later. Yes.

  As the photoreceptor 3 </ b> Y, a drum-like member is used in which a photosensitive layer is formed by applying a photosensitive organic photosensitive material to a base tube made of aluminum or the like. An endless belt may be used.

  The charging device 4Y applies a charging bias to a charging roller disposed so as to be in contact with or close to the surface of the photoconductor 3Y, and generates a discharge between the charging roller and the photoconductor 3Y. The 3Y surface is uniformly charged. Instead of the charging device 4Y having such a configuration, a charging charger that uniformly charges the photoreceptor 3Y by a corotron or a scorotron may be employed.

  The developing device 5Y develops the electrostatic latent image on the photoreceptor 3Y by a so-called two-component developing method using a two-component developer containing a magnetic carrier (not shown) and non-magnetic Y toner. Instead of such a configuration, a configuration of a one-component development system in which development is performed with a one-component developer not including a magnetic carrier may be adopted.

  As the drum cleaning device 6Y, a system that presses a cleaning blade made of polyurethane rubber against the photoreceptor 3Y is used, but another system may be used. The surface of the photoreceptor 3Y cleaned by the drum cleaning device 6Y is subjected to charge removal processing by a charge removal lamp (not shown) and then uniformly charged to a negative polarity by the charging device 4Y.

  A transfer unit 20 is disposed below the four process units 2Y, 2M, 2C, and 2K. In this transfer unit 20, an endless intermediate transfer belt 21 stretched by a plurality of rollers is brought into contact with the photoreceptors 3Y, 3M, 3C, and 3K, and primary transfer for Y, M, C, and K is performed. While forming the nip, the intermediate transfer belt 21 is moved endlessly in the counterclockwise direction in the drawing at a process linear velocity of 150 [mm / sec] by the rotational driving of the driving roller 22.

  In the loop of the intermediate transfer belt 21, a driving roller 22, a tension roller 23, primary transfer rollers 24Y, Y, M, C, and K for Y, M, C, and K, a coating backup roller 25, and a cleaning backup roller 26 are arranged. It is installed. Each of these rollers is a tension roller that stretches the belt around its surface in a loop.

  The tension roller 23 as a tension applying member is configured to be movable in the horizontal direction and applies a constant tension to the intermediate transfer belt 21 by being biased toward the outside of the belt loop by a spring.

  The four primary transfer rollers 24Y, 24M, 24C, 24K are urged toward the photoconductors 3Y, M, C, and K by springs, and the intermediate transfer belt is provided between the photoconductors 3Y, M, C, and K. 21 is sandwiched. As a result, primary transfer nips for Y, M, C, and K where the front surface of the intermediate transfer belt 21 and the photoreceptors 3Y, 3M, 3C, and 3K come into contact are formed. A primary transfer bias of +1800 [V] is applied to each of the primary transfer rollers 24Y, 24M, 24C, 24K by a power source (not shown). As a result, a primary transfer electric field for electrostatically moving the toner images on the photoreceptors 3Y, 3M, 3C, and 3K toward the intermediate transfer belt 21 is formed in the primary transfer nips for Y, M, C, and K. Has been.

  In the figure, the front surface of the intermediate transfer belt 21 that sequentially passes through the primary transfer nips for Y, M, C, and K along with endless movement in the counterclockwise direction is provided with Y, M, C, and K. The toner images are sequentially superimposed and primarily transferred. By this primary transfer of superposition, a four-color superposed toner image (hereinafter referred to as a four-color toner image) is formed on the front surface of the intermediate transfer belt 21.

  A secondary transfer roller 27 is disposed on the right side of the intermediate transfer belt 21 in the figure, and this is in contact with a region where the intermediate transfer belt 21 is wound around the driving roller 22 from the belt front surface side. The next transfer nip is formed. As a result, a secondary transfer nip where the front surface of the intermediate transfer belt 21 and the secondary transfer roller 27 abut is formed.

  A secondary transfer bias is applied to the secondary transfer roller 27 by a power source (not shown). On the other hand, the drive roller 22 in the belt loop is grounded. Thereby, a secondary transfer electric field is formed in the secondary transfer nip.

  A registration roller pair 45 is disposed below the secondary transfer nip in the drawing, and the secondary transfer is performed at a timing at which the recording paper P sandwiched between the rollers can be synchronized with the four-color toner image on the intermediate transfer belt 21. Send to nip. In the secondary transfer nip, the four-color toner images on the intermediate transfer belt 21 are collectively transferred to the recording paper P due to the influence of the secondary transfer electric field and the nip pressure, and become a full color image combined with the white color of the recording paper.

  The secondary transfer roller 27 is a roller in which a surface of a metal core such as stainless steel is covered with an elastic layer made of urethane or the like adjusted to a resistance value of 10E6 to 10E10 [Ω] by a conductive material. When the resistance value of the secondary transfer roller 27 exceeds the above-described range, it becomes difficult for current to flow. Therefore, it is necessary to apply a high voltage to obtain a required transfer property, resulting in an increase in power supply cost. Further, since a high voltage is applied, a discharge occurs in the gap before and after the transfer nip, so that white spots are lost due to the discharge on the halftone image. On the other hand, if the resistance value is less than the above range, transferability between a multi-color image portion (for example, a three-color superimposed image) and a single-color image portion existing on the same image cannot be achieved. This is for the reason explained below. That is, since the resistance value of the secondary transfer roller 27 is too low, a current sufficient to transfer the monochrome image portion with a relatively low voltage flows. On the other hand, since a voltage value higher than the optimum voltage for the single color image portion is required to transfer the multiple color image portion, if the voltage is set such that the multiple color image portion can be transferred, the transfer current will be excessive in the single color image. This is because efficiency is reduced.

  The resistance value of the secondary transfer roller 27 can be measured as follows. That is, the secondary transfer roller 27 is installed on a conductive metal plate, and the metal core and the metal are loaded with a load of 4.9 [N] on one side (total of 9.8 N on both sides) at both ends of the metal core. It is calculated from the current value that flows when a voltage of 1000 V is applied to the plate.

  A driving force is applied to the secondary transfer roller 27 by a driving gear (not shown), and the peripheral speed is adjusted to be substantially the same as the linear speed of the intermediate transfer belt 21.

  The secondary transfer bias applied to the secondary transfer roller 27 is adjusted so that the secondary transfer current flowing between the secondary transfer roller 27 and the belt becomes +30 [μA]. That is, in this printer, the secondary transfer current is controlled to a constant current of +30 [μA].

  Untransferred toner that has not been transferred to the recording paper P at the secondary transfer nip is attached to the front surface of the intermediate transfer belt 21 that has passed through the secondary transfer nip. This transfer residual toner is cleaned by a belt cleaning device 31 that contacts the intermediate transfer belt 21. Specifically, the belt cleaning device 31 presses a cleaning blade made of urethane rubber against the front surface of the intermediate transfer belt 21, and scrapes and removes transfer residual toner on the front surface by the cleaning blade. . The cleaning backup roller 26 in the belt loop is disposed so as to sandwich the intermediate transfer belt 21 with the belt cleaning device 31.

  An application brush roller 29 is disposed on the left side of the belt cleaning device 31 in the drawing and rubs against the front surface of the intermediate transfer belt 21. Further, a solid lubricant 30 is disposed above the application brush roller 29 and is pressed against the application brush roller 29 with a pressure of 1 to 4 [N] by a spring. The application brush roller 29 scrapes the lubricant from the solid lubricant 30 in accordance with the rotational drive to form a lubricant powder, and the lubricant on the front surface of the belt immediately before the cleaning process by the belt cleaning device 31 is performed. Apply powder. Thereby, the slipping between the transfer residual toner and the belt surface is improved, or the sliding between the cleaning blade and the belt surface is improved, thereby improving the cleaning property and the transfer property.

  Examples of the solid lubricant 30 include fatty acid metal salts having a linear hydrocarbon structure. The fatty acid metal salt contains at least one fatty acid selected from stearic acid, palmitic acid, myristic acid, and oleic acid, and at least one selected from zinc, aluminum, calcium, magnesium, and lithium. The fatty acid metal salt containing these metals can be illustrated. In particular, zinc stearate is the most preferred material because of its cost, quality stability, and reliability because it is produced on an industrial scale and has a track record of use in many fields. However, the higher fatty acid metal salts that are generally used industrially include other fatty acid metal salts, metal oxides, and free fatty acids that are more or less similar, rather than the compound composition of the name.

  The length of the solid lubricant 30 in the belt width direction needs to be larger than the image width. In this embodiment, it is set to 304 mm or more. Further, the length of the application brush roller 29 in the rotation axis direction is larger than the width of the solid lubricant 30 in order to uniformly scrape the solid lubricant 30.

  On the left side of the application brush roller 29 in the drawing, the pressing roller 28 is in contact with the intermediate transfer belt 21 so as to bite into the loop from the front surface side. As a result, the vibration of the belt caused by the rubbing with the application brush roller 29 is suppressed. Instead of the configuration that bites into the loop from the front side, a configuration that bites out of the loop from the back side may be adopted. Further, as a member that presses against the belt, a pressure pad or the like that does not take a movement following the belt (sliding on the belt) may be used instead of the pressing roller 28.

The intermediate transfer belt 21 is formed endlessly by a casting method, a centrifugal molding method, or the like, and the surface thereof may be polished as necessary. A belt having a single layer structure or a multilayer structure made of a material made of PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), or the like. Since the conductive material such as carbon black is dispersed in the material, the entire belt has a volume resistivity of 10 ⁸ to 10 ¹² [Ωcm] and a surface resistivity of 10 ⁹ to 10 ¹³ [Ωcm. ] Are adjusted respectively. If the volume resistivity of the intermediate transfer belt 21 exceeds the above-mentioned range, the bias required for the transfer becomes high and the power supply cost increases, which is not preferable. In addition, the belt charging potential in the transfer process, the recording paper peeling process, and the like becomes high, and it becomes difficult to perform self-discharge, so that it is necessary to provide a charge eliminating unit, resulting in an increase in cost. In addition, if the volume resistivity and surface resistivity are below the above ranges, the charging potential decays faster, which is advantageous for static elimination by self-discharge. However, since the current during transfer flows in the surface direction, the toner splatters. Will occur. Therefore, it is preferable to adjust the volume resistivity and the surface resistivity of the intermediate transfer belt 21 within the above-described ranges.

  The volume resistivity and the surface resistivity can be measured as follows. That is, an HRS probe (inner electrode diameter 5.9 mm, ring electrode inner diameter 11 mm) is connected to a high resistivity meter (manufactured by Mitsubishi Chemical Corporation: Hiresta IP), and 100 V on the front and back of the belt (500 V for measuring surface resistivity) The measured value 10 seconds after applying the voltage is used.

  If necessary, a release promoting layer may be coated on the surface of the intermediate transfer belt 21. Materials for the release promoting layer include ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinylidene fluoride), PEA (perfluoroalkoxy fluororesin), FEP ( Examples of the fluororesin include tetrafluoroethylene-hexafluoropropylene copolymer) and PVF (vinyl fluoride), but are not limited thereto.

  The recording sheet P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 61 and sent to the fixing device 50. The fixing device 50 forms a fixing nip by abutting a heating roller 50a including a heat source such as a halogen lamp and a pressure roller 50b pressed toward the heating roller 50a. The recording paper P sandwiched between the fixing nips is subjected to a toner image fixing process by heating and pressing.

  The recording paper P subjected to the fixing process in this manner is discharged out of the apparatus via a pair of paper discharge rollers (not shown).

  As the toner, a polymerized toner manufactured by a polymerization method is used. This polymerized toner has a shape factor SF-1 in the range of 100 to 180 and a shape factor SF-2 in the range of 100 to 180. The shape factor SF-1 is an index value indicating the degree of roundness of the toner particles. As shown in FIG. 2, a value obtained by dividing the square of the maximum length MXLNG of a projected image formed by projecting toner particles on a two-dimensional plane by the area AREA of the projected image and multiplying by 100π / 4 is randomly extracted. The average of 100 toner particles. When the value of the shape factor SF-1 is 100, the shape of most toner particles contained in the toner is a true sphere, and the shape of the toner particles becomes indefinite as the value of SF-1 increases. The shape factor SF-2 is an index value indicating the degree of unevenness of the toner particles. As shown in FIG. 3, a value obtained by dividing the square PERI of the projected image formed by projecting toner particles on a two-dimensional plane by the area AREA of the projected image and multiplying by 100π / 4 is randomly extracted. The average of 100 toner particles. When the value of SF-2 is 100, most of the toner particles contained in the toner have no irregularities, and as the value of SF-2 increases, the irregularities of the toner particles become more prominent.

  The shape factor can be measured as follows. That is, a magnified photograph of the toner particles is taken with a scanning electron microscope (S-800: manufactured by Hitachi, Ltd.), and this is introduced into an image analyzer (LUSEX 3: manufactured by Nireco) and analyzed and calculated. When the shape of the toner is close to a spherical shape, the contact between the toner particles or between the toner and the photoconductor is close to a point contact, so that the fluidity of the toner becomes high and the adsorptive power between the toner and the photoconductor is almost lost. The transfer rate increases. If either of the shape factors SF-1 and SF-2 exceeds 180, the transfer rate is lowered and the cleaning property when attached to the transfer means is also lowered, which is not preferable.

  The toner particle size is preferably in the range of 4 to 10 [μm] in terms of volume average particle size. When the particle size is smaller than this, background stains may occur during development, or voids may easily occur due to deterioration in fluidity and increase in cohesion. On the other hand, when the particle size is larger than this, it becomes impossible to obtain a high-definition image due to toner scattering or resolution deterioration. In the embodiment, a toner having a volume average particle diameter of 6.5 [μm] is used as the toner.

  In FIG. 1 described above, a toner image detection sensor 55 is disposed directly below the intermediate transfer belt 21. The toner image detection sensor is disposed so as to face a region around the tension roller 23 in a circumferential direction of the intermediate transfer belt 21 with a predetermined gap.

  This printer periodically performs process control processing and misregistration correction processing for the purpose of obtaining a stable image density regardless of environmental fluctuations, and suppressing the misalignment of toner images of each color due to changes in internal temperature. It is like that. The process control process is a process for adjusting image forming conditions such as development potentials in the color process units 2Y, 2M, 2C, and 2K so that a desired image density is obtained. Specifically, first, a density detection toner image of each color as a reference toner image is formed on the intermediate transfer belt 21, and the image density is detected by the toner image detection sensor 55. Based on the detection result, the image forming condition (development potential) is adjusted so that the target image density is obtained. In addition, the positional deviation correction processing is performed in accordance with the amount of deviation, in order to reduce the registration deviation of each color toner image caused by a subtle optical path deviation of scanning light due to a temperature change, This is a process for correcting the surface tilt angle of the optical system reflection mirror. Specifically, first, a toner image for detecting misregistration of each color as a reference toner image is detected by the intermediate transfer belt 21, and the relative position thereof is detected by the toner image detection sensor 55. Based on the result, the amount of misregistration of each color is calculated, and the optical writing start timing or the surface tilt angle of the optical system reflection mirror is corrected to a value that can cancel the misregistration amount.

  The intermediate transfer belt 21 shown in FIG. 1 is in a color mode in which toner images of two or more colors are superimposed. In the color mode, as shown in the figure, the intermediate transfer belt 21 is brought into contact with all of the photosensitive members 3Y, 3M, 3C, and 3K of the respective colors to form primary transfer nips for Y, M, C, and K. doing.

  FIG. 4 is a main part configuration diagram showing a state in the printer in the monochrome mode in which only the K toner image is formed. The printer includes contact / separation means for contacting / separating the intermediate transfer belt 21 to three of Y, M, and C among the four photoreceptors 3Y, 3M, 3C, and 3K. This contact / separation means is a belt region from immediately after passing the pressing position by the pressing roller 28 to immediately before entering the primary transfer nip for K in the entire region in the circumferential direction of the intermediate transfer belt 21. By changing the stretching posture of the first region, the first region is brought into contact with and separated from the Y, M, and C photoconductors 3Y, M, and C. The stretching posture of the first region is changed by moving the primary transfer rollers 24Y, 24M, 24C for Y, M, and C substantially in the normal direction of the photoreceptor. Specifically, when the first region is brought into contact with the Y, M, and C photoconductors 3Y, 3M, and 3C, the primary transfer rollers 24Y, 24M, and 24C are attached to the belt as shown in FIG. And move to a position where they contact the photoreceptors 3Y, 3M, 3C. On the other hand, when the first area is separated from the Y, M, and C photoconductors 3Y, M, and C, as shown in FIG. 2, the primary transfer rollers 24Y, M, and C are moved to the photoconductors 3Y, M, and C, respectively. , C is moved greatly in the direction away from C. Then, the first region that has been pressed toward the photoconductors 3Y, 3M, and 3C is separated from the photoconductors 3Y, 3M, and 3C.

  In such a configuration, the tension roller 23 may be greatly moved along with the contact / separation operation by the contact / separation means. Specifically, as shown in FIG. 5, when the intermediate transfer belt 21 changes from a state in which it is in contact with the Y, M, and C photoconductors 3Y, M, and C to a separated state, the intermediate transfer belt 21 The length of the first region at 21 changes. Specifically, in the abutted state, the tension posture of the first region (the pressing roller 28 to the photosensitive member 3K) is a bent shape that forms two sides of the triangle, whereas in the separated state, The tension posture of one area becomes a linear shape. Thereby, in the separated state, the length of the first region is shorter than the contacted state. For this reason, in the configuration shown in FIG. 5, when the state changes from the contacted state to the separated state, a large slack in the tension of the intermediate transfer belt 21 occurs temporarily, and the tension roller 23 eliminates the slack. So that it moves to the left in the figure (from the position of the dotted line to the position of the solid line). On the contrary, when changing from the separated state to the abutted state, the tension of the intermediate transfer belt 21 temporarily increases greatly, and the tension roller 23 moves correspondingly to the right in the figure (solid line). To the dotted line). Then, in either the abutted state or the separated state, it is not possible to face the area around the tension roller 23 directly above the toner image detection sensor, and between the tension roller 23 and the drive roller 22. The belt extension area of the opposite. Since the belt extension region undulates, the detection accuracy of the toner image detection sensor is greatly deteriorated in this state.

Next, a characteristic configuration of the printer according to the embodiment will be described.
Unlike the conventional printer shown in FIG. 5, the printer according to the embodiment is devised so as not to cause the tension roller 23 to move due to the contact / separation operation by the contact / separation means. Specifically, in this printer, reverse tension generating means for generating a tension change in a direction opposite to the tension change caused by the contact / separation operation by the contact / separation means is provided for the intermediate transfer belt 21, and the contact / separation means is used. The reverse tension generating means is operated in accordance with the contact / separation operation.

  FIG. 6 is an enlarged configuration diagram showing each color process unit and a part of the transfer unit of the printer according to the embodiment in an enlarged manner. In the drawing, the intermediate transfer belt 21 is separated from the Y, M, and C photoconductors 3Y, 3M, and 3C by the contact / separation means. The dotted line in the figure shows the stretching posture in the first region of the intermediate transfer belt 21 when the intermediate transfer belt 21 is in contact with the Y, M, and C photoconductors 3Y, M, and C. . Further, the alternate long and short dash line in the figure indicates the first region when the intermediate transfer belt 21 is separated from the Y, M, and C photoconductors 3Y, M, and C by the contacting / separating means and the reverse tension generating means is not operated. This shows the tension posture. As described above, when changing from the dotted line state to the one-dot chain line state, the tension of the intermediate transfer belt 21 is loosened, and the tension roller 23 is moved in the left direction in the drawing following the looseness. There is a risk that. Therefore, the reverse tension generating means operates in synchronization with the operation of the contacting / separating means, and passes through the contact position with the application backup roller (25 in FIG. 1) in the entire area of the intermediate transfer belt 21 in the circumferential direction. A reverse tension is generated by changing the stretching posture of the second region from immediately after to immediately before entering the K primary transfer nip. Specifically, as shown in the drawing, when the contact / separation means separates the intermediate transfer belt 21 from the Y, M, and C photoconductors 3Y, 3M, and 3C, as shown by the arrows in the drawing, the pressing roller 28 is moved in such a direction as to cause it to penetrate more into the loop. As a result, the second region of the intermediate transfer belt 21 is made to penetrate further inside the loop than the one-dot chain line state, and the tension of the intermediate transfer belt 21 is increased. Then, the looseness of the belt tension accompanying the belt separating operation by the contacting / separating means can be reduced by increasing the belt tension by the operation of the reverse tension generating means, and the moving amount of the tension roller 23 due to the tension change can be reduced.

  When the contact / separation means brings the intermediate transfer belt 21 into contact with the Y, M, and C photoconductors 3Y, 3M, and 3C, the press roller 28 is directed further out of the loop, contrary to the separation. Move. As a result, the second region of the intermediate transfer belt 21 is made to penetrate further inside the loop than the one-dot chain line state, and the tension of the intermediate transfer belt 21 is increased. Thereby, the increase in belt tension accompanying the belt contact operation by the contact / separation means is reduced by the slack of the belt tension caused by the operation of the reverse tension generation means, and the amount of movement of the tension roller 23 due to the tension change is reduced.

  As described above, in this printer, the deterioration of the detection accuracy of the toner image detection sensor 55 due to the undulation of the intermediate transfer belt 21 can be suppressed without moving the toner image detection sensor 55 together with the tension roller 23.

  In this printer, the amount of change in the tension posture of the intermediate transfer belt 21 (first region) due to the operation of the contact / separation means, and the tension posture of the intermediate transfer belt 21 (second region) due to the operation of the reverse tension generating means. Are set to the following values, respectively. In other words, the tension change of the intermediate transfer belt 21 due to the change in the tension posture due to the operation of the contact / separation means can be just offset by the reverse tension change due to the operation of the reverse tension generation means. Therefore, the tension roller 23 can be present at a substantially fixed position regardless of the contact / separation operation by the contact / separation means.

  FIG. 7 is a configuration diagram showing the state of the contacting / separating means and the reverse tension generating means when the intermediate transfer belt 21 is in contact with the Y, M, C photoconductors 3Y, 3M, 3C. FIG. 8 is a configuration diagram showing the state of the contacting / separating means and the reverse tension generating means when the intermediate transfer belt 21 is separated from the Y, M, and C photoconductors 3Y, 3M, and 3C. . The contacting / separating means includes a Y transfer roller holder 31Y, an M transfer roller holder 31M, a C transfer roller holder 31C, an arm 33, an eccentric cam 34, a cam motor (not shown), and the like. Each of the three transfer roller holders (31Y, M, C) swings around the rotation shaft (32Y, M, C) while holding the primary transfer roller (24Y, M, C) rotatably. It is possible to move. Each of the lower ends is engaged with an engaging groove provided in the arm 33.

  The arm 33 is configured to be slidable in the horizontal direction, and is urged by a spring 37 toward the right in the drawing. An eccentric cam 34 abuts on the right end of the arm 33 in the figure, and the arm 33 slides in the horizontal direction as the eccentric cam 34 rotates. As the slide moves, the three primary transfer rollers (24Y, M, C) respectively swing and bring the intermediate transfer belt 21 into and out of contact with the photoreceptor (3Y, M, C). In the state of FIG. 7, the position of the arm 33 is fixed at a position where the primary transfer roller (24Y, M, C) is pressed against the photoconductor (3Y, M, C) via the belt. This position adjustment is performed by adjusting the rotation stop position of the eccentric cam 34. When the intermediate transfer belt 21 is separated from the belt, the eccentric cam 24 is rotated by about 180 °, and the arm 33 is slid to the right in the figure as shown in FIG. Then, the primary transfer roller (24Y, M, C) rotates counterclockwise by a predetermined angle, and the intermediate transfer belt 21 is separated from the photosensitive member (3Y, M, C).

  The reverse tension generating means includes an arm 33, an eccentric cam 34, a pressing roller holder 35, a spring 37, a cam motor, and the like. Among these, the arm 33, the eccentric cam 34, the spring 37, and the cam motor are also components of the contacting / separating means as described above. The pressure roller holding body 35 can swing around the rotation shaft 36 in a state where the pressure roller 28 is rotatably held. The lower end of the arm 33 is engaged with the engaging groove of the arm 33. When the arm 33 slides, the pressing roller 28 swings about the rotation shaft 36 and the pressing force on the intermediate transfer belt 21 is increased or decreased. The swing is interlocked with the swing of the three primary transfer rollers (24Y, M, C). This interlocking is realized by the arm 33 as the interlocking mechanism swinging the three transfer roller holders (31Y, M, C) and the pressing roller 28 as the slide moves. Thus, by providing the arm 33 as the interlocking mechanism, it is possible to synchronize the operations of both means without performing troublesome control processing such as simultaneous drive control of the contacting / separating means and the reverse tension generating means. Further, since the cam motor as a drive source is shared by the contacting / separating means and the reverse tension generating means, the cost can be reduced as compared with the case where the cam motor is not shared.

  The contacting / separating means shifts the primary transfer rollers 24Y, 24M, 24C for Y, M, and C, which are members in the loop disposed in the loop of the intermediate transfer belt 21, to a predetermined position and further outside the loop. The tension posture of the first region of the intermediate transfer belt 21 is changed in accordance with the movement between the two positions. In such a configuration, it is possible to reduce the cost by using the existing primary transfer rollers 24Y, 24M, and 24C without providing a dedicated member for the contacting / separating means as the in-loop member.

  Further, the reverse tension generating means moves the intermediate transfer belt 21 between the predetermined position and the position shifted further to the inner side of the loop than the intermediate transfer belt 21. The tension posture of the second region of the belt 21 is changed. In such a configuration, the pressing roller 28 is used as the loop outer member, thereby generating reverse tension and suppressing occurrence of belt vibration due to the application operation of the application brush roller 29. Further, by using the pressing roller 28 which is a loop outer roller that can be driven and rotated as the outer loop member, the life of the intermediate transfer belt 21 can be extended by eliminating the friction between the outer loop member and the belt.

  In FIG. 1 described above, the application brush roller 29 as a lubricant application means for applying a lubricant to the front surface of the intermediate transfer belt 21 is located at the belt position before entering the contact position with the pressing roller 28. On the other hand, it is disposed at a position where the coating process is performed. In such a configuration, the lubricant applied to the front surface of the belt by the application brush roller 29 can be leveled by the pressing roller 28 to make the lubricant uniform.

  FIG. 9 is a main part configuration diagram showing a modified example of the printer according to the embodiment. FIG. 10 is a principal configuration diagram showing the same modified example in a state where the intermediate transfer belt 21 is separated from the Y, M, and C photoconductors 3Y, 3M, and 3C. In the printer according to the modified example, the contact portion of the Y, M, and C photoconductors 3Y, M, and C as the specific image carrier with the intermediate transfer belt 21, that is, the primary transfer for Y, M, and C is performed. The photoreceptors 3Y, 3M, and 3C are arranged on a straight line so that the nip is positioned on the same virtual straight line. This configuration is the same as that of the printer according to the embodiment, but the position of the K photoconductor 3K is different from that of the embodiment. Specifically, the K photoconductor 3 </ b> K is disposed so that the K primary transfer nip is positioned inward of the belt loop with respect to the virtual straight line. As described above, when the K photoconductor 3K is shifted and disposed, the K photoconductor 3K is the same as the other photoconductors, as can be seen from a comparison between FIGS. 9 and 10 and FIGS. The intermediate transfer belt 21 can be brought into and out of contact with the Y, M, and C photoconductors 3Y, 3M, and 3C with fewer belt operations than in the case of being arranged on a straight line. Thereby, size reduction and cost reduction of the transfer unit 20 can be realized.

  So far, an example of a printer using an intermediate transfer belt as a belt member has been described. However, as a belt member, a paper conveyance belt that conveys the recording paper held on its surface and passes the recording paper through the primary transfer nip of each color. The present invention can also be applied to an image forming apparatus using the above.

  Further, an example in which a part of the second region, which is a belt region whose tension posture is changed by the reverse tension generating means, and the first region, which is a belt region whose tension posture is changed by the contacting / separating means, are overlapped. However, the two regions need not overlap at all.

  As described above, in the printer according to the embodiment, the arm 33 is provided as an interlocking mechanism for interlocking the reverse tension generating unit with the contacting / separating unit, so that troublesome control processing of simultaneous drive control of the contacting / separating unit and the reverse tension generating unit is performed. It is possible to synchronize the operation of both means without doing so.

  In the printer according to the embodiment, the tension change of the intermediate transfer belt 21 caused by the change in the tension posture due to the operation of the contact / separation unit is set to a value that can be canceled by the reverse tension change by the reverse tension generation unit. The amount of change in the tension posture in the first region due to the operation of the contacting / separating means and the amount of change in the tension posture in the second region due to the operation of the reverse tension generating means are set. In such a configuration, the tension roller 23 can be substantially in a fixed position regardless of the contact / separation operation by the contact / separation means.

  Further, in the printer according to the embodiment, as a specific image carrier for contacting and separating the belt, the contact and separation means for the photoreceptors 3Y, M, and C that carry Y, M, and C toner images different from black. Thus, the first region is brought into contact with and separated from the first region. The photoreceptor 3K carrying K toner is brought into contact with the intermediate transfer belt 21 regardless of the operation of the contact / separation means. In such a configuration, in the monochrome mode, the photoconductor that does not contribute to image formation can be separated from the belt, and unnecessary power consumption can be suppressed, and wear of the photoconductor and the belt can be suppressed.

  Further, in the printer according to the embodiment, since the toner image detection sensor 55 is disposed at a position facing the wrapping region with respect to the tension roller 23, it is possible to suppress deterioration in detection accuracy due to waving of the belt.

  In the printer according to the modification, the first region is brought into contact with and separated from the Y, M, and C photoconductors 3Y, M, and C by a contact / separation unit as a specific image carrier. . While arranging the photoconductors 3Y, M, and C on a straight line so that the primary transfer nips for Y, M, and C by the photoconductors 3Y, M, and C are positioned on the same virtual straight line, Regardless of the operation of the contact / separation means, the K primary transfer nip by the K photoconductor 3K brought into contact with the belt is positioned at a position shifted to the inside of the belt loop from the virtual line. In such a configuration, as already described, the intermediate transfer belt 21 is moved to the Y, M, C with less belt operation than the case where the K photoconductor 3K is arranged on a straight line as well as the other photoconductors. Can be brought into contact with or separated from the photosensitive members 3Y, 3M, 3C.

  Further, in the printer according to the embodiment, since the same cam motor is shared by the contacting / separating means and the reverse tension generating means, the cost can be reduced as compared with the case where they are not shared.

  Further, in the printer according to the embodiment, as the contact / separation means, the in-loop member disposed in the loop of the intermediate transfer belt 21 is moved between a predetermined position and a position shifted to the outside of the loop. Along with this, a device that changes the stretching posture of the first region is used. In such a configuration, it is possible to reduce the cost by using the existing primary transfer rollers 24Y, 24M, and 24C without providing a dedicated member for the contacting / separating means as the in-loop member.

  Further, in the printer according to the embodiment, as a reverse tension generating unit, a loop outer member disposed outside the loop of the intermediate transfer belt 21 is moved between a predetermined position and a position shifted to the inner side of the loop. Along with this, a device that changes the stretching posture of the second region is used. In such a configuration, a pressing roller can be used as the loop outer member.

  Further, in the printer according to the embodiment, a pressing roller that is a freely driven outer loop is used as the outer loop member, and therefore, the length of the intermediate transfer belt 21 can be reduced by eliminating friction between the outer loop member and the belt. Life can be extended.

Further, in the printer according to the embodiment, the belt portion before the application brush roller 29 as the lubricant application means for applying the lubricant to the front surface of the intermediate transfer belt 21 enters the contact position with the pressing roller 28. It arrange | positions in the position which performs a coating process with respect to. In such a configuration, the lubricant applied to the front surface of the belt by the application brush roller 29 can be leveled by the pressing roller 28 to make the lubricant uniform.

  Further, in the printer according to the embodiment, since the pressing roller 28 is disposed in the vicinity of the application brush roller 29, the generation of belt vibration due to rubbing against the application brush roller 29 can be suppressed by the pressing roller 28. .

3Y, M, C, K: photoconductor (image carrier)
20: Transfer unit (transfer means)
21: Intermediate transfer belt (belt member)
23: Tension roller (tension applying member)
24Y, M, C, K: Primary transfer roller (loop inner member)
28: Pressing roller (loop outer member)
33: Arm (interlocking mechanism)
55: Toner image detection sensor (toner image detection means)
P: Recording paper (recording member)

JP 2008-9011 A Japanese Patent No. 3473346

Claims (9)

A plurality of image carriers that carry toner images on their surfaces;
The toner images respectively carried on the surfaces of the image carriers are held on the front surface of an endless belt member that is endlessly moved in a state of being stretched by a plurality of stretching members, or held on the front surface. Transfer means for transferring to the recording member,
A tension applying member that applies a tension to the belt member by urging the belt inner member disposed in the loop of the belt member toward the outside of the loop of the belt member while abutting the back surface of the belt member;
A toner image detecting means for detecting a toner image transferred to the front surface and disposed near a tensioning region with respect to the tension applying member among all the regions in the circumferential direction of the front surface of the belt member. When,
The contact / separation of contacting / separating the first region with one or more specific image carriers in accordance with a change in the stretching posture of a predetermined first region different from the hanging region in the circumferential direction of the belt member. An image forming apparatus comprising:
As the contact / separation means, the tension of the first region is increased as the inner member of the loop disposed in the loop of the belt member is moved between a predetermined position and a position shifted to the outside of the loop. Use something that changes the rack posture,
As the contacting / separating means changes the stretching posture of the first region, the loop outer member disposed outside the loop of the belt member shifts to a predetermined position and to the inner side of the loop. By changing the tension posture of the predetermined second region different from the wrapping region in the belt member as the belt member is moved between the positions, the belt member is moved by the operation of the contact / separation means. A reverse tension generating means for generating a tension change in a direction opposite to the tension change caused by the change in the tension posture is provided .
In addition, a lubricant application means for applying a lubricant to the front surface of the belt member is disposed at a position where an application process is performed on the belt portion before entering the contact position with the loop outer member . An image forming apparatus. The image forming apparatus according to claim 1.
An image forming apparatus comprising an interlocking mechanism for interlocking the reverse tension generating unit with the contacting / separating unit. The image forming apparatus according to claim 1 or 2,
The tension of the first region by the operation of the contacting / separating means is set to a value that can cancel the tension change of the belt member due to the change of the tension posture by the operation of the contacting / separating means by the tension change in the reverse direction. An image forming apparatus, wherein a change amount of a posture and a change amount of a stretching posture of the second region due to the operation of the reverse tension generating unit are set. The image forming apparatus according to any one of claims 1 to 3,
As the specific image carrier, the first region is brought into contact with and separated from the image carrier carrying a toner image of a color different from black by the contact and separation means,
An image forming apparatus characterized in that an image carrier carrying black toner is brought into contact with the belt member regardless of the operation of the contact / separation means. The image forming apparatus according to any one of claims 1 to 4,
An image forming apparatus, wherein the toner image detecting means is disposed at a position facing the wrapping area. The image forming apparatus according to claim 1,
As the specific image carrier, the first region is brought into contact with or separated from the two or more image carriers by the contact and separation means,
While disposing the two or more image carriers in a straight line so that the contact portion of the two or more image carriers with the first region is located on the same virtual straight line,
Regardless of the operation of the contact / separation means, the contact portion with the belt member in the image carrier to be brought into contact with the belt member is located at a position shifted from the virtual straight line to the inner side of the loop of the belt member. An image forming apparatus. The image forming apparatus according to claim 1,
An image forming apparatus, wherein the contact / separation unit and the reverse tension generation unit share the same drive source. The image forming apparatus according to claim 1 ,
An image forming apparatus using a loop outer roller that can be driven and rotated as the outer loop member. The image forming apparatus according to claim 1 ,
As the lubricant applying means, a means for applying a lubricant to the belt member by a brush member is used,
An image forming apparatus, wherein the outer loop member is disposed in the vicinity of the lubricant applying means.

Images