JP2010217852A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent image rubbing which may be generated between a fixing device and a paper sheet by making first and second intermediate transfer means and the fixing device to be at a constant speed in one-pass both side simultaneous transfer. <P>SOLUTION: In an image forming device, a first image carrier forms a first toner image and makes primary transfer to a first intermediate transfer means, a second image carrier forms a second toner image and makes transfer to a second intermediate transfer means, and each toner image is secondarily transferred simultaneously on both sides of a recording medium and conveyed to the fixing device. At least one of the first and second intermediate transfer means has a conveyance function. The image forming device performs pre-rotation of the first and second intermediate transfer means and the fixing device before performance of image forming and controls so that the line speeds of them should be at a constant speed in image forming. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus for transferring a toner image to both surfaces of a recording medium such as transfer paper by a so-called one-pass method to form an image.

  2. Description of the Related Art Some image forming apparatuses such as copying machines, printers, and facsimiles are configured to form images on both sides of a recording medium (hereinafter referred to as paper). In a conventional image forming apparatus capable of double-sided recording, an image on one side formed on an image carrier is transferred to a sheet directly or via an intermediate transfer unit and fixed, and the sheet is reversed by a reversing path or the like. A two-pass method is generally used in which the paper is fed again and the image on the other side is transferred and fixed on the back side of the paper.

  In the case of double-sided recording by this method, there are many problems in securing the reliability of paper conveyance due to switching of the paper conveyance direction and paper curl by fixing a single-sided image. There is also a problem of image failure due to transfer failure to curled paper.

  As a system for solving these problems and transferring the toner images to both sides of the paper, the first image carrier and the second image carrier are used to transfer the toner images onto both sides of the paper, and then during one transport. There has been proposed a one-pass system in which fixing is performed. There are a method using a plurality of transfer processes and a method using a single transfer, that is, a method using simultaneous transfer of both front and back sides of the paper using toner polarity conversion (Patent Document 1).

  By the way, in the case of the conventional two-pass method, a method is adopted in which the image carrier and the intermediate transfer unit, and the intermediate transfer unit and the sheet are provided with a difference in linear velocity to prevent the omission of lines and characters. Reference 2). This is to apply a shearing force between the image carrier and the intermediate transfer unit, or between the intermediate transfer unit and the paper, thereby faithfully performing the transfer from the image carrier to the intermediate transfer unit or from the intermediate transfer unit to the paper. It is. Also disclosed is a technique for changing the fixing speed in order to increase the glossiness of the paper (Patent Document 3).

  In particular, in the one-pass method, a method is proposed in which a paper transport device is disposed between the intermediate transfer unit and the fixing device to stably transport the paper and prevent the toner image from being disturbed. In this case, as a paper transport device, a transport system using a spur (Patent Document 4), a transport system using a belt (Patent Document 5, Patent Document 6, and Patent Document 7) and a belt are used, and air is further sucked. There is a method (Patent Document 8). In addition, a configuration example in which a sheet conveyance function is added to one of the intermediate transfer units has already been proposed (Patent Document 9).

  In the case of the one-pass double-sided simultaneous transfer method, the toner image is present on both the front and back sides when transferring to the paper, so the friction coefficient between the paper and each belt is lower than when no toner image is provided.

  In addition, when a linear velocity difference is provided in order to obtain a shearing force between the paper and the belt during paper transfer as in Patent Document 2 (two-pass method), the friction coefficient between the paper and the belt is low on both the front and back sides. Not only the shearing force cannot be obtained, but also the paper moves while rubbing against the belt.

  Specifically: When the linear velocity difference is provided, the paper is conveyed along one linear velocity of the intermediate transfer body, although the friction coefficient between the paper and the belt is low. At this time, since the paper moves (slides) while rubbing against the other belt, the toner image on the rubbing belt cannot be transferred to the normal position of the paper, and the front end in the transport direction The image is transferred while being rubbed to the side or the rear end side. If an image formed product is obtained by passing through the fixing device in this state, an image in which the toner image is stretched, so-called image rubbing, will occur.

  When the paper is transported along a belt with a slow linear speed, the toner image of the belt with a fast linear speed extends toward the front end in the transport direction, and when the paper is transported along a belt with a fast linear speed, The rubbing of the image in which the toner image of the belt having a low linear velocity extends toward the rear end side in the conveying direction occurs.

  FIG. 11 is an explanatory diagram schematically illustrating this. When the normal image schematically illustrated in FIG. 11A is rubbed, for example, as schematically illustrated in FIG. The image will be rubbed.

  Further, as in Patent Document 3, if the fixing linear speed is slowed down in order to obtain a glossy image, that is, if the sheet conveying speed and the fixing linear speed of the intermediate transfer member are different, the sheet follows the fixing linear speed with a strong conveying force, and the sheet It moves while rubbing against the intermediate transfer member.

  Specifically: When the leading edge of the paper enters the fixing device, the linear speed of the paper also decreases along the fixing device having a slow linear speed. At this time, since the sheet is in contact with the belt while holding the unfixed toner image, the sheet is struck with the belt when the linear velocity of the sheet becomes slow. The unfixed toner image is rubbed at the rubbing portion and deviated from the normal position, so that a so-called image rub that an image is stretched occurs.

  When a paper transport device is provided as in Patent Documents 4, 5, 6, 7, and 8, the number of paper delivery times between the devices increases. For this reason, the discharge phenomenon that occurs when the paper is peeled off (when the paper is peeled off from the intermediate transfer member and the transport device) and the discharge phenomenon that occurs when the paper is landed (when the paper is landed on the transport device and the fixing device) increase. Disturbance of the unfixed toner image that is generated increases the occurrence of so-called toner dust.

  Further, the drive control becomes complicated due to an increase in the number of devices that adjust the speed, and further, since the sheet conveying device has to be incorporated, an increase in the size of the device is inevitable.

  In Patent Documents 1 and 9, it is possible to reduce the size of the apparatus by adding a paper transport function to the intermediate transfer unit. However, since the configuration described in Patent Document 9 controls the speed of only the intermediate transfer unit depending on the paper type, When there is a difference in linear velocity between the fixing device and the intermediate transfer unit, image rubbing always occurs as described above. Furthermore, since the unfixed toner image is interposed between the intermediate transfer member and the sheet when the sheet is conveyed, the sheet attracting force is low, and the sheet is conveyed while fluttering.

  When the paper flutters, the paper holding the unfixed toner image repeatedly contacts and separates from the belt. When the paper contacts, the paper and the belt rub against each other, and the unfixed toner image is rubbed. A minute gap is formed between the belts, and the unfixed toner image is disturbed by a discharge phenomenon generated in the gap.

  Patent Documents 5, 6, 7, and 9 propose speed control of each device, but a specific control method and speed are not disclosed. Further, Patent Document 9 describes an example in which the paper type is detected and the speed is controlled during paper conveyance. In this case, in order to obtain stable paper conveyance, for example, Patent Document 8 If the sheet and the transport device or the intermediate transfer unit are attracted to each other by an external force (air suction in Patent Document 8), the speed of the transport device or the intermediate transfer unit fluctuates before and after the external force is applied.

  At this time, if there is no toner image, the frictional force between the paper and the conveying device or the intermediate transfer means is sufficiently high so that the paper does not slip. However, in the case of 1-pass double-sided simultaneous transfer, the toner image is interposed. Therefore, the coefficient of friction between the sheet and the conveying device or the intermediate transfer unit becomes low, the sheet cannot follow the speed fluctuation due to the external force, and so-called image rubbing in which the image is extended to the rear end side occurs.

  Table 1 is a comparison table with each cited document.

  The object of the present invention is to provide an image forming apparatus capable of preventing image rubbing and obtaining a high-quality image output product. Another object of the present invention is to provide an image forming apparatus capable of downsizing the apparatus.

  That is, an object of the present invention is to prevent image rubbing that occurs between each device and paper by making the first and second intermediate transfer means and the fixing device constant speed in one-pass double-sided simultaneous transfer. . By determining the control value so that the linear velocity is constant by pre-rotating each device, it is possible to effectively prevent image rubbing due to speed fluctuations that occur when adjustment is performed during paper conveyance. Furthermore, by providing a transport function to the second intermediate transfer unit, the apparatus can be reduced in size.

  In order to solve the above problems, an image forming apparatus according to the present invention includes a first image carrier and a second image carrier as image carriers on which an electrostatic latent image is written and visualized on an outer peripheral surface to form a toner image. An image carrier, the first image carrier forms a first toner image and primarily transfers it to a first intermediate transfer means, and the second image carrier forms a second toner image. In an image forming apparatus in which primary transfer is performed to a second intermediate transfer unit, and the first and second toner images are simultaneously secondarily transferred onto both surfaces of a recording medium in a transfer unit, and then the recording medium is conveyed to a fixing device. At least one of the first and second intermediate transfer units has a transport function of transporting the recording medium to the fixing device, and the first and second intermediate transfer units and the fixing device before image formation is performed. Speed control value so that the linear speed of each of these three is equal Determined individually, the first by even at the time of image formation using said speed control value groups, is characterized by controlling the linear velocity of the linear velocity and the fixing device of the second intermediate transfer section to a constant speed.

  In the image forming apparatus described above, the first and second intermediate transfer units and the fixing device are driven by independent drive sources. The image forming apparatus may further include a detection unit that detects a linear speed of the first and second intermediate transfer units and the fixing device, and the driving sources are controlled based on a detection result of the detection unit. It is characterized by controlling.

  In the image forming apparatus according to any one of the above, when the linear speeds of the first and second intermediate transfer members and the fixing device are controlled at a constant speed, the linear speed of any one of the apparatuses is used as a reference. It is characterized by controlling the linear velocity of the other two devices. In the image forming apparatus according to any one of the above, when the linear velocities of the first and second intermediate transfer members and the fixing device are controlled to be constant, the three linear devices are used with respect to a reference linear velocity. The speed is controlled simultaneously.

  The image forming apparatus according to any one of the above, further comprising an electrostatic attracting unit configured to apply a bias to the second intermediate transfer unit and the recording medium when the recording medium is transported to electrostatically attract them. The biasing is performed by the electrostatic attraction unit even during pre-rotation for controlling the linear velocity of the second intermediate transfer unit and the fixing device at a constant speed. In any of the above image forming apparatuses, the first image carrier and the second image carrier have toner of the same polarity, and the second image carrier forms a second toner image. And a polarity reversing charger for inverting the charging polarity of the second toner image on the second intermediate transfer unit after transfer to the second intermediate transfer unit, and the first and second intermediate transfer units, In the pre-rotation for controlling the linear velocity of the fixing device at a constant speed, bias application is performed by the polarity reversing charger.

  In the image forming apparatus described above, the electrostatic attraction unit is a charger for electrostatic attraction, and the charger applies a bias from the back surface of the second intermediate transfer unit. In the image forming apparatus described above, the electrostatic attraction unit is a non-contact charger for electrostatic attraction, and the non-contact charger applies a bias from the surface of the second intermediate transfer unit.

  In the image forming apparatus according to any one of the above, a plurality of first image carriers and second image carriers are arranged in tandem along the first intermediate transfer unit and the second intermediate transfer unit. The first toner images are superimposed on the first intermediate transfer means to form the first color image by sequentially transferring the first toner images from the first image carriers, and the second intermediate transfer means. The second toner image is superimposed on each second image carrier and sequentially transferred to form a second color image, and the first color image and the second color image are transferred to the transfer unit. After the secondary transfer on both sides of the recording medium, the recording medium is conveyed to a fixing device.

  According to the present invention, an image forming apparatus capable of preventing image rubbing and obtaining a high-quality image output product at any time of transfer to a sheet, conveyance of a sheet carrying an unfixed toner image, and fixing of the sheet. Can be obtained. In the case where the transfer function is added, the size of the apparatus can be reduced.

1 is a schematic configuration diagram illustrating a first embodiment of an image forming apparatus according to the present invention. FIG. 3 is an enlarged cross-sectional view schematically showing a configuration of an image forming unit in the first embodiment. (A)-(c) is a schematic block diagram which shows the Example of the drive control mechanism (speed detection function part) in 1st Embodiment apparatus, respectively. 6 is a flowchart illustrating a control method for making the transport surface moving speeds of the first intermediate transfer unit, the second intermediate transfer unit, and the fixing device constant in Embodiment 1. 10 is a flowchart for controlling the linear speeds of the first intermediate transfer unit, the second intermediate transfer unit, and the fixing device in Example 2 so as to be simultaneously equal to a preset reference linear speed. It is an expanded sectional view showing typically the composition of the image forming part of other embodiments concerning the present invention. It is an expanded sectional view showing typically the composition of the image forming part of other embodiments concerning the present invention. 10 is a flowchart illustrating a control method for making the transport surface moving speeds of the first intermediate transfer unit, the second intermediate transfer unit, and the fixing device constant in Example 4. 14 is a flowchart for controlling the linear speeds of the first intermediate transfer unit, the second intermediate transfer unit, and the fixing device in Example 4 so as to be simultaneously equal to a preset reference linear speed. It is the expanded sectional view which showed typically the structure of the tandem-type image formation part of other embodiment which concerns on this invention. 6 is an example of an image schematically showing image rubbing in an image forming process.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a first embodiment of an image forming apparatus according to the present invention. FIG. 2 is an enlarged cross-sectional view schematically showing a configuration of a main part (hereinafter referred to as an image forming unit 120) mainly related to image forming processing of the same image forming apparatus. The image forming apparatus shown in FIG. 1 includes a first image carrier and a second image carrier as image carriers (photosensitive members), and optically writes an image corresponding to image information to each image carrier. Then, after development, the image forming apparatus is capable of forming an image by fixing the front and back images after transferring the images onto the front and back surfaces of the transfer paper through the intermediate transfer means. However, the main part (hereinafter referred to as the image forming unit 120) that performs the main image forming process is simply shown as a block in FIG. 1 and the configuration is omitted. FIG. 2 is an enlarged cross-sectional view schematically showing the detailed configuration of the image forming unit 120. The present invention can be implemented not only for the above-described copying machine but also for a printer, a facsimile machine, a printing machine, or a multifunction peripheral (MFP) as an image forming apparatus.

  First, an outline of the configuration of the entire copying machine according to the present embodiment will be described. As shown in the schematic configuration diagram of FIG. 1, the copying machine includes a copying machine main body 100, a paper feed table 200 on which the copying machine main body 100 is placed, a scanner 300 mounted on the copying machine main body 100, An automatic document feeder (ADF) 400 attached to the upper part of the scanner 300 is configured.

  An image forming unit 120 is disposed substantially at the center of the copying machine main body 100 (see FIG. 2 for details). Moreover, the control part 160 is provided (a structure is known and it does not explain in particular in this specification). In practice, the control units 160 are appropriately distributed. In the image forming apparatus, as well known, the image forming unit 120 forms an image based on image information read by the scanner 300 or image information transmitted from an external client device.

  That is, in the case of a copying operation, the user first sets a document on the document table 130 of the automatic document feeder (ADF) 400 or opens the automatic document feeder 400 and puts it on the contact glass 32 of the scanner 300. The document is set and the automatic document feeder 400 is closed.

  Subsequently, when a start switch (not shown) is pressed and a copy start command is input, each roller in the image forming unit, the paper feed conveyance path, and the like starts to rotate at a predetermined timing. When a document is set on the automatic document feeder 400, after the document is transported and moved onto the contact glass 32, on the other hand, when the document is set on the contact glass 32, the scanner 300 is driven immediately. The first traveling body 33 and the second traveling body 34 travel. At this time, light from the light source is irradiated by the first traveling body 33 and reflected light from the document surface is reflected by the mirror in the second traveling body 34 and is received by the reading sensor 36 through the imaging lens 35 to be received by the document. (Image) is read and converted into image information. The image information is transmitted to the image forming unit 120, and a toner image is formed in the image forming unit 120 to obtain a copy.

  In the case of a printing operation, a print command including character information and / or image information to be printed is received from an external client device, and the image information is directly converted into image information by the image forming unit 120. Corresponding image formation (printing) is performed.

  The configuration of each unit for image formation and the image forming operation will be described in detail. The image forming unit 120 includes two sets of image forming units 1a and 1b for monochrome images. Each of the image forming units 1a and 1b includes photoconductors 2a and 2b as image carriers using a drum. Around the photoconductors 2a and 2b, images are rotated in the rotation process indicated by arrows in FIG. Charging devices 3a, 3b, writing devices 4a, 4b (only the optical path L is shown in FIG. 2), developing devices 5a, 5b, first intermediate transfer means 6a, second intermediate transfer means for executing the forming process 6b, photoconductor cleaning devices 12a and 12b, and static eliminating devices 13a and 13b are arranged, respectively. Note that the first intermediate transfer unit 6a and the second intermediate transfer unit 6b referred to in the present specification refer to an overall mechanism that includes the intermediate transfer belts 61a and 61b as a main body and includes related parts for intermediate transfer. And

  In the copying machine main body 100, the image forming units 1a and 1b are parallel to each other, and in the rotation process of the photoconductors 2a and 2b, after the uniform charging process by the charging devices 3a and 3b, the photoconductors are optically written according to image information. An electrostatic latent image is formed on 2a and 2b, and the electrostatic latent image is subjected to a visible image processing with an image forming substance (hereinafter referred to as toner) supplied from the developing devices 5a and 5b to form a toner image. In the present embodiment, toners of different polarities are used in the developing devices 5a and 5b, the developing device 5a supplies negative polarity toner, and the developing device 5b supplies positive polarity toner.

  Next, the first intermediate transfer unit 6a and the second intermediate transfer unit 6b, which are provided corresponding to the photoconductors 2a and 2b, respectively, have toner images formed on the photoconductors 2a and 2b, respectively. The transfer belts 61a and 62b are partly transferred, and the transfer belts 61a and 62b are transferred again to the recording medium P fed from the paper feeding device in the paper feeding table 200. After the toner image is transferred, the toner image transferred onto the recording paper provided on the downstream side in the transport direction is transported and fixed to a fixing device 25 for fixing, so that a final image output product is obtained. . The fixing device 25 will be described in more detail later.

  As the toner image is formed, one of the paper feed rollers 142 is selectively rotated on the lower paper feed table 200 to record from a paper feed cassette (tray) provided in multiple stages in the paper bank 143. The feeding of the medium (sheet) P is started. The recording medium P is fed out from one of the paper feed cassettes 144, separated one by one by the separation roller 145, and sent to the paper feed path 146. Then, the sheet is conveyed by the conveyance roller 147 and guided to the paper feed path in the image forming apparatus main body 100, and is abutted against the registration roller 149 via the conveyance roller 148 and stopped.

  On the other hand, the registration roller 149 starts rotating in accordance with the timing at which the toner images formed on the transfer belts 61a and 62b are conveyed to the secondary transfer unit as described above. The registration roller 149 is generally used while being grounded, but may be used in a state in which a bias is applied to remove the paper dust of the recording medium P.

  In this way, the recording medium P conveyed from the paper feeding unit is fed to the nip portion between the transfer belts 61a and 62b by the registration roller 149 in accordance with the timing of image formation on the photoconductors 2a and 2b. The toner images developed on 2a and 2b are transferred onto a recording medium P sandwiched between transfer belts 61a and 62b.

  Unnecessary toner on the photoreceptors 2a and 2b is removed by the photoreceptor cleaning devices 12a and 12b. In this embodiment, blade cleaning is employed, but rollers and brushes can also be used. Thereafter, the surface potential of the photoconductor is neutralized by the neutralization devices 13a and 13b, and the process proceeds to the next image forming process. In this embodiment, the static elimination is performed by the static elimination lamp, but a static elimination method using a roller or a charger can also be used.

  As the transfer belts (hereinafter, also simply referred to as belts) 61a and 61b, a belt material (endless belt) having a three-layer structure of a base layer, an elastic layer, and a coat layer is used. In the case of a belt having a three-layer structure, the base layer is made of a material obtained by combining, for example, a fluorine-based resin having a small elongation or a rubber material having a large elongation with a material that is difficult to stretch, such as a canvas. The elastic layer is made of, for example, fluorine rubber or acrylonitrile-butadiene copolymer rubber, and is formed on the base layer. The coat layer is formed by coating the surface of the elastic layer with, for example, a fluorine resin. The transfer belts 61a and 62b are composed of single layer or multiple layers of PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), or the like. Can also be used.

Moreover, you may coat a release layer on the surface of belt 61a, 61b as needed. Materials used for the surface coating include ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinylidene fluoride), PEA (perfluoroalkoxy fluororesin), FEP (four Fluorine resins such as fluorinated ethylene-hexafluoropropylene copolymer) and PVF (vinyl fluoride) can be used, but are not limited thereto.
The manufacturing method of the belts 61a and 61b includes a casting method, a centrifugal molding method, and the like, and the surface thereof may be polished if necessary.

  The belts 61a and 61b have a resistivity adjusted by dispersing a conductive material such as carbon black, and have a volume resistivity of 10 ^ 8 to 10 ^ 12 Ωcm and a surface resistivity of 10 ^ 9 to 10 ^ 13 Ωcm. It is desirable to adjust the range.

  The volume resistivity and surface resistivity of the belts 61a and 61b are not limited to the above ranges. However, if the volume resistivity of the belts 61a and 61b exceeds the above range, the bias required for transfer increases. There is a possibility of increasing the cost. In addition, the charging potential of the belts 61a and 61b becomes high in the transfer process, the transfer paper peeling process, and the like, and self-discharge becomes difficult. If the volume resistivity and surface resistivity are below the above ranges, the charge potential decays faster, which is advantageous for static elimination by self-discharge. However, toner scatter may occur because the current during transfer flows in the surface direction. There is.

  The volume resistivity and surface resistivity were measured by connecting an HRS probe (inner electrode diameter 5.9 mm, ring electrode inner diameter 11 mm) to a high resistivity meter (Mitsubishi Chemical Corporation: Hiresta IP), and the front and back of the belt 6A. A voltage of 100 V (surface resistivity is 500 V) was applied to the measured value after 10 seconds.

As a configuration for transferring the toner images carried on the photoreceptors 2a and 2b to the belts 61a and 61b, in this embodiment, the image carrying surfaces of the belts 61a and 61b using the primary transfer rollers 62a and 62b as transfer means. Bias is applied from the opposite side (back side).
In this embodiment, the primary transfer roller is used as the primary transfer unit. However, the roller that stretches the belts 61a and 61b can also be used as the primary transfer unit, or a contact type transfer unit other than the roller. Alternatively, non-contact type transfer means such as a transfer charger can also be used.

  The toner carried on the belts 61a and 61b is simultaneously transferred to the recording medium P by the secondary transfer rollers 65a and 65b (secondary transfer). In this embodiment, by applying a negative bias to the secondary transfer roller 65a and grounding the secondary transfer roller 65b, the toner image carried on the belt 61a is carried on the belt 61b using repulsive force. The toner image is electrostatically transferred to the recording medium P using an attractive force. In the present embodiment, the secondary transfer rollers 65a and 65b are in contact with each other, but a mechanism capable of contacting or separating either one or both may be provided.

  The belt 61a of the first intermediate transfer means 6a is stretched by three rollers, a drive roller 63a, a driven roller 64a, and a secondary transfer roller 65a, and is attached to the drive roller 63a by using the first intermediate transfer motor 21a and a mechanism (not shown). Power is applied to rotate in the direction of the arrow in the figure.

  The belt 61b of the second intermediate transfer means 6b is stretched by four rollers of a drive roller 63b, driven rollers 64b and 66b, and a secondary transfer roller 65b, and is driven by using the second intermediate transfer motor 21b and a mechanism (not shown). Power is applied to 63b to rotate in the direction of the arrow in the figure. Further, by providing a linear portion to the secondary transfer roller 65b and the driven roller 66b, the conveyance function of the recording medium P 1 is given. However, the number of rollers for stretching the belts 61a and 61b is not limited to the number illustrated in the drawing.

  A belt cleaning device 67a is provided on the outer periphery of the belt 61a. Further, on the outer periphery of the belt 61b, there are provided a belt cleaning device 67b and a charger 8 and a counter electrode 9 which are charging means for electrostatically adsorbing the recording medium P to the belt 61b during conveyance. The belt cleaning device 67a has a function of removing unnecessary toner remaining on the surface of the belt 61a, and the removed toner is conveyed to a collection container (not shown). In this embodiment, blade cleaning is performed, but rollers and brushes may be used.

  In this embodiment, a corotron charger is used for the electrostatic attraction charger 8 and a bias having the same polarity as the bias applied to the secondary transfer roller 65a is applied to transfer the toner image on the recording medium P (transfer material). While suppressing the scattering, the recording medium P is conveyed to the fixing device 25 by adsorbing the belt 61b. The transfer sheet S that has passed through the fixing device 25 is discharged and stacked on a discharge tray 57 by a discharge roller 56.

  The fixing device 25 includes fixing rollers 27a and 27b having heat sources, and is rotated in the arrow direction in the figure by the fixing motor 22 and a mechanism (not shown). Both the fixing rollers 7a and 7b have the same structure. That is, it has an elastic layer such as silicone rubber or fluororubber on the cored bar with a built-in heater, and the surface is coated with a releasable coat layer of fluororesin. The roller hardness is equal, and the value is JIS standard The JIS-A hardness is set in a range of 25 to 50 Hs by measurement according to (JIS K6301). Since both fixing rollers are made of the same material and have the same structure, their surface characteristics are the same. Therefore, the image quality on both sides of the sheet after fixing can be made equal.

  In addition, by making the hardness of the fixing rollers 7a and 7b in the range of 25 to 50Hs in JIS-A hardness, it is possible to obtain a reliable fixing performance. When the hardness is lower than 25 Hs, the nip surface pressure at the time of pressurization is low, and the toner may be insufficiently melted to cause a fixing failure. Further, if the hardness is higher than 50 Hs, there is a possibility that a nip width necessary for fixing cannot be obtained.

  Here, the drive control mechanism (speed detection function unit) of the first intermediate transfer unit 6a, the second intermediate transfer unit 6b, and the fixing device 25 will be described according to an embodiment shown in the schematic configuration diagram of FIG. FIG. 3A is a configuration diagram schematically showing an enlarged end portion of the driving roller 63a whose rotational speed corresponds to the moving speed of the first intermediate transfer unit 6a. In the configuration shown in FIG. 3A, the driving roller 63b whose rotational speed corresponds to the moving speed of the second intermediate transfer unit 6b, and the rotational speed determines the recording paper conveyance speed in the fixing device 25 (correspondence relationship). The same applies to the fixing roller 27a on the driving side, which is shown separately in FIGS. 3 (b) and 3 (c).

  As shown in each drawing of FIG. 3, the shafts of the drive rollers 63a and 63b and the fixing roller 27a, that is, the shafts 631a, 631b, and 271a are provided with encoder disks 632a, 632b, and 272b, respectively. The encoder disks 632a, 632b, and 272b are provided with a large number of slits radially in the circumferential direction. And detection part 633a, 633b, 273b is arrange | positioned so that the front-end | tip part of encoder disk 632a, 632b, 272b may be straddled. The detection units 633a, 633b, and 273b are well-known optical sensors. The detection units 633a, 633b, and 273b have a light emitting unit and a light receiving unit, and can detect the light emitted from the light emitting unit and passing through the slits of the encoder disks 632a, 632b, and 272b. It has become. When each roller rotates, the detection units 633a, 633b, and 273b output a pulse-shaped detection signal, and the control unit 160 performs speed control based on the detection signal and a clock signal from an appropriate clock circuit. . In this embodiment, speed detection using an encoder disk is performed. However, for the first intermediate transfer unit 6a and the second intermediate transfer unit 6b, marks attached to the intermediate transfer belts 61a and 61b are read speed control. It is also possible to perform speed control using other methods such as

  Next, a control method for making the transport surface moving speeds of the first intermediate transfer unit 6a, the second intermediate transfer unit 6b, and the fixing device 25 constant, which is a characteristic point of the present embodiment, will be described.

  FIG. 4 is a flowchart for controlling the linear speeds of the second intermediate transfer member 6b and the fixing device 7 to be constant with reference to the linear speed of the first intermediate transfer member 6a. However, this flowchart describes only the part related to the speed control of the first intermediate transfer unit 6a, the second intermediate transfer unit 6b, and the fixing device 25, and other image forming parts (such as rotation control of the photoreceptors 2a and 2b). Is omitted.

  First, when an image signal is input (step S01), the first intermediate transfer motor 21a, the second intermediate transfer motor 21b, and the fixing motor 22 are turned on, and the belts 61a and 61b and the fixing device 25 rotate (pre-rotate) ( Step S02). However, if the fixing device 25 is constantly rotating in order to stabilize the fixing temperature, it is not necessary to turn on the motor again in this flow. Next, a bias is applied to the electrostatic adsorption charger 8 (step S03).

  In order to calculate the linear velocity Vt1 of the first intermediate transfer unit 6a, the linear velocity Vt2 of the second intermediate transfer unit 6b, and the linear velocity Vf of the fixing device 25 after the bias application, the unit minute time from the detection mechanism shown in FIG. The number of per output pulses is detected, and the control unit 160 calculates the moving speed (that is, the linear velocity) in the transport path unit using a predetermined calculation formula, and stores it in the storage unit (step S04). In this embodiment, since the linear speed adjustment is controlled based on the linear speed Vt1 of the first intermediate transfer means 6a, if Vt1 is different from the specified linear speed, the linear speed adjustment of Vt1 is performed at this time. Is more preferable.

  Next, it is determined whether Vt1 and Vt2 are constant speed (Vt1 = Vt2) (step S05). When the line speeds are different (step S05: No), it is determined whether the line speed of Vt2 is fast or slow with reference to the line speed of Vt1 (step S06), and the line speed of Vt2 is made close to Vt1 according to the result. Adjust the motor speed. That is, if Vt1 <Vt2 (step S06: Yes), the linear velocity of the second intermediate transfer means 6b is lowered (step S07). If Vt1 <Vt2 is not satisfied (step S06: No), the second intermediate transfer is performed. The linear velocity of the means 6b is increased (step S08). Thereafter, the linear velocity Vt2 of the second intermediate transfer means 6b is detected (calculated) (step S09), and it is determined again whether the linear velocity of Vt1 and Vt2 is constant (step S05). This linear speed adjustment (step S06 to step S09, step S05) is repeated until Vt1 and Vt2 become constant speeds (until a predetermined small difference).

  If Vt1 and Vt2 become constant speed by the linear speed adjustment (step S05: Yes), it is then determined whether Vt1 and Vf are constant speed (Vt1 = Vf) (step S10). In addition, when Vt1 and Vt2 are constant speed (step S05: Yes), it progresses to (step S10) immediately. In step S10, when the line speeds are different (step S10: No), it is determined whether the line speed of Vf is fast / slow with reference to the line speed of Vt1 (step S11). Adjust the motor speed so that the speed approaches Vt1. That is, if Vt1 <Vf (step S11: Yes), the linear velocity Vf of the fixing unit is lowered (step S12). If Vt1 <Vf is not satisfied (step S11: No), the linear velocity Vf of the fixing unit is set. Up (step S13). Thereafter, the linear velocity Vf of the fixing unit is detected (calculated) (step S14), and it is determined again whether the linear velocity of Vt1 and Vf is constant (step S10). This linear speed adjustment is repeated until Vt1 and Vf become equal speeds (until a predetermined small difference). When Vt1 and Vf become constant speed (Vt1 = Vt2 = Vf), writing is started (step S15), and predetermined image forming processing is sequentially performed.

  In this way, in the present embodiment, pre-rotation before image formation is performed, and control is performed so that the linear speeds of the first intermediate transfer unit 6a, the second intermediate transfer unit 6b, and the fixing device 25 are constant, Image formation is performed. In this embodiment, the control is performed based on the linear velocity Vt1 of the first intermediate transfer unit 6a. However, the control may be performed based on the linear velocity Vt2 and the fixing linear velocity Vf of the second intermediate transfer unit 6b.

  In the present embodiment, the first intermediate transfer unit 6a, the second intermediate transfer unit 6b, and the drive source motor that drives the fixing device 25 are independent motors. If the first intermediate transfer unit 6a, the second intermediate transfer unit 6b, and the fixing device 25 are driven by a single motor, the linear speed of each device may vary depending on the accuracy of parts such as gears, assembly accuracy, or thermal expansion. May occur. This linear velocity difference is difficult to adjust as long as it is driven by one motor, and as a result, the image is rubbed. In addition, the configuration of the drive system is complicated, which may increase the size of the apparatus.

  In order to prevent these problems, in the present embodiment, the first intermediate transfer unit 6a, the second intermediate transfer unit 6b, and the motor for driving the fixing device 25 are independent of each other, thereby simplifying the drive system. Yes. Moreover, since each is controlled independently, each linear velocity can be adjusted with high accuracy. Furthermore, since the linear speed of the first intermediate transfer unit 6a, the second intermediate transfer unit 6b, and the fixing device 25 is controlled to be constant by pre-rotation before image formation, recording that carries an unfixed toner image is performed. The medium P can move at a constant speed with the belts 61a and 61b fixing device 25. Accordingly, it is possible to prevent image rubbing that occurs when the recording medium P is conveyed and when the recording medium P is transferred from the belt 61b to the fixing device 25.

[Example 1]
The following double-sided image passing experiment was conducted with the apparatus of this embodiment.
1) Passing test paper type with plain paper: Type 6200 (Ricoh)
The linear speed of the first intermediate transfer unit 6a was set to 282 mm / sec, and the linear speeds of the second intermediate transfer unit 6b and the fixing device 25 were controlled to be constant according to the flowchart of FIG. There was no image rubbing of the fixed image even when one sheet was passed, 10 sheets were continuously passed, and 10K sheets were passed for a long time. (Table 2)

2) Test paper type with cardboard: Copy printing paper <135> (NBS Ricoh)
The linear speed of the first intermediate transfer means 6a is set to half of the linear speed when passing plain paper: 141 mm / sec, and the linear speeds of the second intermediate transfer means 6b and the fixing device 25 are according to the flowchart of FIG. The speed was controlled. There was no image rubbing of the fixed image even when one sheet was passed, 10 sheets were continuously passed, and 10K sheets were passed for a long time. (Table 3)

[Comparative Example 1]
In Comparative Example 1, a linear velocity difference is given to the first intermediate transfer member 6a and the second intermediate transfer member 6b with respect to the form of Example 1, and the linear velocity of the second intermediate transfer member 6b and the fixing device 7 is made constant. Is. Although the speed adjustment of each device is adjusted to a preset linear velocity, it is not determined whether the speed is constant among the devices.

A double-sided image passing experiment was conducted in the same manner as in Example 1 in the form of Comparative Example 1.
1) Passing test paper type with plain paper: Type 6200 (Ricoh)
Linear velocity: Set each device as follows. First intermediate transfer member 6a... 280 mm / sec.
Second intermediate transfer member 6b... 282 mm / sec
Fixing device 7 ... 282mm / sec
When one sheet was passed, 10 sheets were continuously passed, and 10K sheets were passed for a long time, image rubbing occurred on the first intermediate transfer member 6a side (referred to herein as the surface). (Table 2)

2) Test paper type with cardboard: Copy printing paper <135> (NBS Ricoh)
Line speed: Set each device as follows. First intermediate transfer member 6a ... 140 mm / sec
Second intermediate transfer member 6b ... 141 mm / sec
Fixing device 7 ... 141mm / sec
When one sheet was passed, 10 sheets were continuously passed, and 10K sheets were passed for a long time, image rubbing occurred on the first intermediate transfer member 6a side (front surface). (Table 3)

[Comparative Example 2]
In Comparative Example 2, the linear velocity of the first intermediate transfer member 6a and the second intermediate transfer member 6b is constant, and the linear velocity difference is given to the second intermediate transfer member 6b and the fixing device 7 as compared with the form of Example 1. Is. Although the speed adjustment of each device is adjusted to a preset linear velocity, it is not determined whether the speed is constant among the devices.

A double-sided image passing experiment was performed in the same manner as in Example 1 in the form of Comparative Example 2.
1) Passing test paper type with plain paper: Type 6200 (Ricoh)
Linear velocity: Set each device as follows. First intermediate transfer member 6a... 282 mm / sec.
Second intermediate transfer member 6b... 282 mm / sec
Fixing device 7 ... 280mm / sec
When one sheet was passed, 10 sheets were continuously passed, and 10K sheets were passed for a long time, image rubbing occurred on the second intermediate transfer member 6b side (referred to here as the back side). (Table 2)

2) Test paper type with cardboard: Copy printing paper <135> (NBS Ricoh)
Linear velocity: Set each device as follows. First intermediate transfer member 6a... 141 mm / sec.
Second intermediate transfer member 6b ... 141 mm / sec
Fixing device 7 ... 140mm / sec
When one sheet was passed, 10 sheets were continuously passed, and 10K sheets were passed for a long time, image rubbing occurred on the first intermediate transfer member 6b side (back surface). (Table 3)

[Example 2]
The second embodiment is different from the first embodiment only in a method for controlling the linear speeds of the first intermediate transfer member 6a, the second intermediate transfer member 6b, and the fixing device 7 to be constant. Therefore, description of parts other than control is omitted.

  FIG. 5 is a flowchart for controlling the linear speeds of the first intermediate transfer body 6a, the second intermediate transfer body 6b, and the fixing device 7 so as to be simultaneously equal to the preset reference linear speed.

  This flowchart also describes only the portions related to the speed control of the first intermediate transfer member 6a, the second intermediate transfer member 6b, and the fixing device 7, and other image forming portions (rotations of the photosensitive members 2a, 2b, etc.) are omitted. ing.

  First, when an image signal is input (step S01), the first intermediate transfer motor 21a, the second intermediate transfer motor 21b, and the fixing motor 22 are turned on, and the belts 61a and 61b and the fixing device 25 rotate (pre-rotate) ( Step S02). However, if the fixing device 25 is constantly rotating in order to stabilize the fixing temperature, it is not necessary to turn on the motor again in this flow. Next, a bias is applied to the electrostatic adsorption charger 8 (step S03).

  In order to calculate the linear velocity Vt1 of the first intermediate transfer unit 6a, the linear velocity Vt2 of the second intermediate transfer unit 6b, and the linear velocity Vf of the fixing device 25 after the bias application, the unit minute time from the detection mechanism shown in FIG. The number of per output pulses is detected, and the control unit 160 calculates the moving speed (that is, the linear velocity) in the transport path unit using a predetermined calculation formula, and stores it in the storage unit (step S04).

  Next, it is determined whether or not the Vt1, Vt2, and Vtf are the same (Vt1 = Vt2 = Vf) as the preset “reference” linear velocity (step S21). If all are the same (constant speed), writing is started as it is and image formation is performed (step S15).

  When the “reference” linear velocity is different from Vt1, Vt2, and Vf, it is determined whether the “reference” is equal to each linear velocity (steps S22, S27, S32). The line speed is adjusted according to whether the line speed is fast or slow.

  The adjustment method will be described below. First, it is determined whether the “reference” linear velocity and Vt1 are equal (step S22). If the linear speeds are different, it is determined whether or not the Vt1 linear speed is higher than the reference (step S23), and the Vt1 linear speed is adjusted according to whether the linear speed is fast or slow (steps S24 and S25).

  The linear velocity Vt2 and the fixing linear velocity Vf of the second intermediate transfer member are also performed simultaneously with the linear velocity adjustment of Vt1. In the control method, the above-described Vt1 is replaced with Vt2 and Vf, respectively (steps S27 to S30, S32 to S35).

  When the linear velocity adjustment for all of Vt1, Vt2, and Vf is completed, the respective linear velocity is detected (steps S26, S31, and S36), and it is determined again whether the “reference” linear velocity is the same as Vt1, Vt2, and Vtf (step). S21). If all the linear velocities are constant, writing is started, and if they are different, linear velocity adjustment is performed again.

The following double-sided image passing experiment was conducted in the form of Example 2.
1) Passing test paper type with plain paper: Type 6200 (Ricoh)
The reference linear velocity was set to 282 mm / sec, and the linear velocity of the first intermediate transfer member 6a, the second intermediate transfer member 6b, and the fixing device 7 was controlled to be constant according to the flowchart of FIG.

  There was no image rubbing of the fixed image even when one sheet was passed, 10 sheets were continuously passed, and 10K sheets were passed for a long time.

2) Test paper type with cardboard: Copy printing paper <135> (NBS Ricoh)
The reference linear velocity is set to plain paper: half of the linear velocity at the time of paper feeding: 141 mm / sec, and the linear velocity of the first intermediate transfer member 6a, the second intermediate transfer member 6b, and the fixing device 7 follows the flowchart of FIG. , And controlled to be constant speed.

  There was no image rubbing of the fixed image even when one sheet was passed, 10 sheets were continuously passed, and 10K sheets were passed for a long time.

[Example 3]
FIG. 6 shows a different embodiment of the image forming apparatus. Compared with the first embodiment, the apparatus according to this embodiment has a configuration in which charging means for electrostatic attraction is disposed on the back side of the image carrying surface of the belt 61b.

  Since the configuration and control other than the charging means for electrostatic attraction are the same as in the first embodiment, description of the configuration and operation of each part in the present embodiment that is common to the first embodiment is omitted.

  Note that the method of the second embodiment (flowchart in FIG. 5) can be adopted as a method for controlling the linear speeds of the first intermediate transfer member 6a, the second intermediate transfer member 6b, and the fixing device 7 to be constant. .

  In the present embodiment, the metal roller 11 is disposed on the back surface of the belt 61b as a charging means for electrostatic adsorption. A bias having a polarity opposite to that applied to the secondary transfer roller 65a is applied to the metal roller 11, and in the second embodiment, the secondary transfer roller 65a has a negative polarity and the metal roller has a positive polarity. Thereby, the scattering of the toner image on the recording medium (transfer material) P is suppressed, and the recording medium P is attracted to the belt 61b and conveyed to the fixing device 25.

  Also in the form of the third example, the double-sided image passing experiment was performed when the line speed (282 mm / sec) for plain paper and the line speed (141 mm / sec) for thick paper were set as in the first embodiment. As a result, at any linear speed, there was no image rubbing of the fixed image when one sheet was passed, 10 sheets were continuously passed, and 10K sheets were passed for a long time.

[Example 4]
The control according to the present invention can be applied even when a pair of developing devices uses toner charged to the same polarity. FIG. 7 shows a configuration in which the developing devices 5a and 5b use toner having the same polarity as in the first embodiment. In addition, description here is abbreviate | omitted about the structure and control which are common in 1st Embodiment.

  Also in this embodiment, the configuration is such that electrostatic transfer is simultaneously performed on both surfaces by the secondary transfer rollers 65a and 65b. Therefore, when the developing devices 5a and 5b supply toner having the same polarity, it is necessary to convert one of the toner polarities to a reverse polarity.

  Therefore, in this embodiment, polarity conversion (polarity inversion) is performed on the second intermediate transfer unit 6b for "-toner (image)" supplied from the developing device 5b and forming a toner image. For this polarity conversion, the polarity reversing charger 10 and the counter electrode 14 are used, and by applying a + bias, the toner polarity on the belt 6b is converted to + to obtain "+ toner (image)". Yes. In this embodiment, the corotron charger is used as the polarity reversing charger 10, but other non-contact type charging devices can also be used.

  The toner image (−polarity) on the belt 61a and the toner image (+ polarity) on the belt 61b are generated by applying a negative bias to the secondary transfer roller 65a and grounding the secondary transfer roller 65b. The toner image carried on the belt 61a is electrostatically transferred to the recording medium P using repulsive force, and the toner image carried on the belt 61b is electrostatically transferred using attractive force.

  Next, a control method for making the linear speeds of the first intermediate transfer unit 6a, the second intermediate transfer unit 6b, and the fixing device 25 corresponding to the present embodiment constant will be described with reference to the flowchart of FIG. Since only a part of the control method of the first embodiment (FIG. 4) is different, only the different part will be mainly described.

  First, when an image signal is input (step S01), the first intermediate transfer motor 21a, the second intermediate transfer motor 21b, and the fixing motor 22 are turned on, and the belts 61a and 61b and the fixing device 25 are pre-rotated (step S02). . However, if the fixing device 25 is constantly rotating in order to stabilize the fixing temperature, it is not necessary to turn on the motor again in this flow.

  Next, a bias is applied to the electrostatic adsorption charger 8 and the polarity reversing charger 10 (step S03 '). Subsequent processes for controlling each apparatus at a constant speed are the same as those in FIG. 4 described in the first embodiment, and are therefore omitted.

  As a method for controlling the linear speeds of the first intermediate transfer member 6a, the second intermediate transfer member 6b, and the fixing device 7 to be constant, the method of simultaneously adjusting the linear speeds of the devices as in the second embodiment is used. Is also possible. In this case, it is sufficient to apply a bias to both the electrostatic adsorption charger 8 and the polarity conversion charger 10 in the portion to which the electrostatic adsorption charger 8 is applied in the flowchart of FIG. (FIG. 9).

  In Example 4, a double-sided image passing experiment was conducted when the linear speed (282 mm / sec) for plain paper and the linear speed (141 mm / sec) for thick paper were set as in the first embodiment. Even at a linear speed of 1, a fixed image was not rubbed when one sheet was passed, 10 sheets were continuously passed, and 10K sheets were passed for a long time.

  In this embodiment, the charger 10 for adsorbing the recording medium P to the belt 61b performs non-contact charging by the corotron charger from the image carrying surface side of the belt 61b. However, the belt as in the second embodiment. A method of electrostatic attraction from the back side of the image carrying surface 61b may be employed.

[Example 5]
FIG. 10 shows that the image forming unit 120 has four image forming units, cyan (Cy), yellow (Ye), magenta (Ma), and black (Bk), which are arranged in this order in the configuration of the fourth embodiment. The tandem method is adopted. The image bearing member includes a plurality of photosensitive drums 2aY, 2aM, 2aC, 2aK, 2bY, 2bM, 2cC, and 2bK arranged in tandem.

  The toner image developed on each photoconductor is transferred from the opposite side (back side) of the belt 61a, 61b to the image carrying surface of each of the primary transfer rollers 62aY, 62aM, 62aC, 62aK, 62bY, 62bM, 62bC, 62bK. A bias is applied and transferred to the belts 61a and 61b.

  Since the configuration other than the above and the control for making the linear speeds of the first intermediate transfer unit 6a, the second intermediate transfer unit 6b, and the fixing device 25 constant are the same as those in the fourth embodiment, I will omit the explanation.

  In Example 5, a double-sided image passing experiment was conducted when the linear speed (282 mm / sec) for plain paper and the linear speed (141 mm / sec) for thick paper were set as in the first embodiment. Even at the linear speed of 1, the fixed image was not rubbed when one sheet was passed, 10 sheets were continuously passed, and 10K sheets were passed for a long time.

  In the present embodiment, as a charger for attracting the recording medium P to the belt 61b, non-contact charging is performed by a corotron charger from the image carrying surface side of the belt 61b. A method of electrostatic attraction from the back side of the image carrying surface may be used.

  In this embodiment, toners having the same polarity are used in the image forming unit 1a and the image forming unit 1b. However, as in the first embodiment, toners having different polarities are used in the image forming unit 1a and the image forming unit 1b. It is also possible to use it. However, in this case, the charger 10 for reversing the toner polarity and the counter electrode 14 are not required, and the linear speeds of the first intermediate transfer unit 6a, the second intermediate transfer unit 6b, and the fixing device 25 are made constant. The control follows the flowchart of FIG. 4 or 5 for each image forming unit of each color.

  In each of the embodiments described above, the image carrier is a photosensitive drum, but a belt-type image carrier can also be used. Further, the configuration of the charging unit, the developing device, the transfer unit, or the fixing device for the image carrier is not limited to the configuration of the above-described embodiment, and an appropriate method can be adopted.

  Further, in each embodiment, the image forming units are arranged above and below the transfer site, but can also be arranged in the left-right direction. It is also possible to arrange the tension direction of the intermediate transfer belt as the intermediate transfer means of the image forming units 1a and 1b in different directions (for example, the image forming unit 1a is arranged in the horizontal direction and the image forming unit 1b is arranged in the vertical direction). It is.

1a, 1b Image forming unit 2a, 2b Photosensitive member (image carrier)
3a, 3b Charging device 4a, 4b Writing device (exposure device)
5a, 5b Developing device 6a First intermediate transfer unit 6b Second intermediate transfer unit 61a, 61b Intermediate transfer belt (intermediate transfer unit)
62a, 62b Primary transfer roller (primary transfer means)
63a, 63b Driving roller 632a, 632b Encoder disk 633a, 633b Detector (optical sensor)
64a, 64b, 66b driven roller 65a, 65b secondary transfer roller (secondary transfer means)
67a, 67b Belt cleaning device 8 Charger (charging means)
9 Counter electrode 10 Charger (for polarity reversal)
11 Charging roller 12a, 12b Photoconductor cleaning device 13a, 13b Static elimination device (static elimination lamp)
14 Counter electrode 21a First intermediate transfer motor 21b Second intermediate transfer motor 22 Fixing motor 25 Fixing device 27a, 27b Fixing roller 272b Encoder disk 273b Detector (optical sensor)
DESCRIPTION OF SYMBOLS 100 Copier main body 120 Image forming part 200 Paper feed table 300 Scanner 400 Automatic document feeder (ADF)
P Recording medium (transfer paper)

JP 2003-223020 A JP 2004-302422 A JP 2001-183925 A Japanese Patent Laid-Open No. 11-344848 JP 2005-017558 A JP 2006-227289 A JP 2006-227292 A JP 2006-001686 A JP 2006-251246 A

Claims (10)

As an image carrier on which an electrostatic latent image is written on the outer peripheral surface and visualized to form a toner image, the image carrier has a first image carrier and a second image carrier,
The first image carrier forms a first toner image and performs primary transfer to the first intermediate transfer unit, and the second image carrier forms a second toner image and transfers to the second intermediate transfer unit. In the image forming apparatus in which the first and second toner images are simultaneously secondarily transferred onto both sides of the recording medium in the transfer unit, and then the recording medium is conveyed to a fixing device.
At least one of the first and second intermediate transfer units has a transport function of transporting the recording medium to the fixing device, and before the image formation is performed, the first and second intermediate transfer units and the fixing device Pre-rotation is performed, and speed control values are individually determined so that the linear speeds of each of the three are equal, and the line of the first and second intermediate transfer means is used by using the speed control value group also at the time of image formation. An image forming apparatus, wherein the speed and the linear speed of the fixing device are controlled to be constant.   The image forming apparatus according to claim 1, wherein the first and second intermediate transfer units and the fixing device are driven by independent driving sources.   The first and second intermediate transfer units and a detection unit that detects a linear velocity of the fixing device, and the drive sources are controlled based on a detection result of the detection unit. The image forming apparatus described in 1.   When the linear speeds of the first and second intermediate transfer members and the fixing device are controlled to be constant, the linear speeds of the other two devices are controlled based on the linear velocity of any one of the devices. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   2. The linear speeds of the three apparatuses are simultaneously controlled with respect to a reference linear speed when the linear speeds of the first and second intermediate transfer members and the fixing device are controlled to be constant. 4. The image forming apparatus according to any one of items 1 to 3.   An electrostatic attracting means for applying a bias to the second intermediate transfer means and the recording medium when the recording medium is conveyed and electrostatically attracting the two; and the first and second intermediate transfer means and the fixing device; 6. The image forming apparatus according to claim 1, wherein a bias is applied by the electrostatic attraction unit even during pre-rotation for controlling the linear velocity at a constant velocity.   The first image carrier and the second image carrier have toner of the same polarity, and a second toner image is formed by the second image carrier and transferred to the second intermediate transfer means, and then the second intermediate transfer And a polarity reversing charger for reversing the charging polarity of the second toner image on the means for controlling the linear speeds of the first and second intermediate transfer means and the fixing device at a constant speed. 6. The image forming apparatus according to claim 1, wherein bias application is performed by the polarity inversion charger even during pre-rotation.   8. The image forming apparatus according to claim 6, wherein the electrostatic attraction unit is a charger for electrostatic attraction, and the charging unit applies a bias from the back surface of the second intermediate transfer unit.   8. The image forming apparatus according to claim 6, wherein the electrostatic attraction unit is a non-contact charger for electrostatic attraction, and the non-contact charger applies a bias from the surface of the second intermediate transfer unit.   A plurality of first image carriers and a plurality of second image carriers are arranged in tandem along the first intermediate transfer unit and the second intermediate transfer unit, respectively. The first toner image is superimposed on the image carrier and sequentially transferred to form a first color image, and the second toner is transferred from the second image carrier to the second intermediate transfer unit. The images are superimposed and sequentially transferred to form a second color image, and the first color image and the second color image are secondarily transferred onto both sides of the recording medium in the transfer unit, and then the recording is performed. The image forming apparatus according to claim 1, wherein the medium is conveyed to a fixing device.

Images