Abstract:
An image forming apparatus includes a first image carrier that carries a first latent image. A first charging section charges the first image carrier. A first exposure section exposes the first image carrier charged by the first charging section. A first developing section develops the first latent image formed on the first image carrier in the first exposure section using a first liquid developer containing a carrier and first toner particles. A first primary transfer section transfers a first image developed in the first developing section onto a transfer medium. A second image carrier carries a second latent image. A second charging section charges the second image carrier. A second exposure section exposes the second image carrier charged by the second charging section.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from prior Japanese Patent Applications No. 2007-338910 filed on Dec. 28, 2007 and No. 2008-289429 filed on Nov. 12, 2008, the entire contents of which are incorporated herein by reference. 
       1. TECHNICAL FIELD 
       [0002]    The present invention relates to an image forming apparatus that forms a color image by superposing liquid developer of a plurality of colors and a control method of the image forming apparatus and, more particularly, to an image forming apparatus that carries out a transfer process of transferring a developed image formed on an image carrier onto a transfer medium such as an intermediate transfer belt for each color liquid developer to form a color image onto the transfer medium and a control method of the image forming apparatus. 
       2. DESCRIPTION OF THE RELATED ART 
       [0003]    There have been proposed various types of wet-developing image forming apparatuses that develops a latent image using a high-viscosity liquid developer obtained by dispersing solid toner particles in a solvent to visualize an electrostatic latent image. A developer used in this wet-developing image forming apparatus is prepared by suspending solid content (toner particles) in a high-viscosity electric insulating organic solvent (carrier liquid) such as a silicon oil, mineral oil, or edible oil. The toner particles are so micronized as to have a particle diameter of about 1 μm. By use of such micro toner particles in a wet-developing image forming apparatus, relatively high quality can be achieved as compared to a dry-developing image forming apparatus using toner powder particles having a particle diameter of about 7 μm. 
         [0004]    As an image forming apparatus of such a type, there is known one disclosed in, e.g., Patent Document 1: JP-A-2006-126258. In this image forming apparatus, image forming stations of different colors are arranged along a transfer medium such as a transfer belt. In each image forming station, a charging unit, an image writing unit, and a developing unit are arranged around a latent image carrier such as a photosensitive drum. Toner images formed by the respective image forming stations are superposed on the transfer medium, whereby a color image is formed. 
         [0005]    Color shift is considered as one of the most serious problem in an image forming apparatus having a plurality of image forming stations. The color shift is caused when transfer positions of respective toner images formed in different image forming stations are relatively shifted from one another and appears as a change in the color tone. To eliminate this problem, the following approach is taken: reference pattern images (hereinafter, referred to as “resist marks”) for detecting color shift is previously formed on a transfer medium; the respective resist marks are detected using an optical sensor to acquire position information of the resist marks; and positioning (color shift compensation processing, displacement compensation processing) of respective toner images are performed based on the acquired position information. 
         [0006]    The processing of compensating color shift in the image forming apparatus disclosed in JP-A-2006-126258 is described in connection with  FIG. 12  and the like of the cited document. As shown in  FIG. 12 , resist marks YRM (yellow resist mark), MRM (magenta resist mark), CRM (cyan resist mark), and KRM (black resist mark) are formed, as toner images, in this order onto an intermediate transfer belt  41  through an ordinary image forming operation executed immediately after power-on. At this time, image forming timing is controlled so that the resist marks YRM, MRM, CRM, and KRM are formed on a reference position S 0 . However, as shown in  FIG. 12 , there is a case where the resist marks MRM, CRM, and KRM are formed at positions shifted from the reference position S 0  by Sm, Sc, and Sk, respectively, in the scanning direction X of a laser beam due to an apparatus assembly error. This error can be compensated/eliminated by changing the image forming timing (scanning timing of the optical beam  21 ) so that image positions are shifted by Sm, Sc, and Sk which are measured by a sensor such as a CCD camera. 
       SUMMARY 
       [0007]    In a wet-developing image forming apparatuses using a liquid developer obtained by dispersing toner particles in a high-viscosity non-volatile carrier liquid, a carrier liquid on the intermediate transfer belt is indispensable for secondary transfer of a toner image onto a recording medium such as a paper in an image forming process. However, a toner image containing the carrier liquid on the intermediate transfer belt has high specularity, which may cause the resist marks to erroneously be detected by a photo-detecting sensor. That is, at the color shift compensation processing time in the image forming apparatus disclosed in Patent Document 1, resist mark detection results obtained by a sensor such as a CCD camera may degrade in accuracy, with the result that accurate position information of the resist marks cannot be obtained, thus preventing accurate color shift compensation. 
         [0008]    In order to cope with this problem, a method can be considered in which the carrier liquid on the intermediate transfer belt is removed at the color shift compensation processing time. However, when the carrier liquid on the intermediate transfer belt is removed, solid content ratio in the resist marks is increased. When the resist marks on the intermediate transfer belt proceed in the process downstream and pass through a secondary transfer nip, the solid content ratio in the resist marks is further increased. Then, there arises a new problem that cleaning performance when cleaning the resist mark transferred onto the intermediate transfer belt by means of a cleaning blade is deteriorated. 
         [0009]    The present invention has been made to solve the above problem and, according to a first aspect of the present invention, there is provided an image forming apparatus including: a first image carrier; a first charging section that charges the first image carrier; a first exposure section that exposes the first image carrier charged by the first charging section; a first developing section that develops a latent image formed on the first image carrier in the first exposure section using a first liquid developer containing a carrier and first toner particles; a first primary transfer section that transfers a first image developed in the first developing section onto a transfer medium; a second image carrier; a second charging section that charges the second image carrier; a second exposure section that exposes the second image carrier charged by the second charging section; a second developing section that develops a latent image formed on the second image carrier in the second exposure section using a second liquid developer containing a carrier and second toner particles; a second primary transfer section that transfers a second image developed in the second developing section onto a transfer medium; a carrier removal section of a transfer medium that removes the carrier from the first and second images transferred on the transfer medium; a condition storage section that stores a first condition in which the carrier removal amount in the transfer medium carrier removal section is set to a first carrier removal amount and a second condition in which the carrier removal amount in the transfer medium carrier removal section is set to a second carrier removal amount smaller than the first carrier removal amount; an optical sensor that detects the first and second images transferred on the transfer medium, from which the carrier has been removed under the first condition stored in the condition storage section; and a distance calculation section that calculates the distance between the first and second images detected by the optical sensor. 
         [0010]    In the image forming apparatus according to the present invention, the transfer medium carrier removal section is a roller, and the rotation direction of the roller differs between the first and second conditions. 
         [0011]    The image forming apparatus according to the present invention further includes a second transfer medium carrier removal section that removes a carrier from the first image transferred on the transfer medium. 
         [0012]    According to a second aspect of the present invention, there is provided an image forming apparatus including: a first image carrier; a first charging section that charges the first image carrier; a first exposure section that exposes the first image carrier charged by the first charging section; a first developing section that develops a latent image formed on the first image carrier in the first exposure section using a first liquid developer containing a carrier and first toner particles; a first image carrier carrier removal section that removes the carrier from a first image developed in the first developing section; a first primary transfer section that transfers the first image from which the carrier has been removed in the first image carrier carrier removal section onto a transfer medium; a second image carrier; a second charging section that charges the second image carrier; a second exposure section that exposes the second image carrier charged by the second charging section; a second developing section that develops a latent image formed on the second image carrier in the second exposure section using a second liquid developer containing the carrier and second toner particles; a second image carrier carrier removal section that removes the carrier from a second image developed in the second developing section; a second primary transfer section that transfers the second image from which the carrier has been removed in the second image carrier carrier removal section onto a transfer medium; a condition storage section that stores a first condition in which the carrier removal amount in the first image carrier carrier removal section or second image carrier carrier removal section is set to a first carrier removal amount and a second condition in which the carrier removal amount in the first image carrier carrier removal section or second image carrier carrier removal section is set to a second carrier removal amount smaller than the first carrier removal amount; an optical sensor that detects the first image transferred on the transfer medium, from which the carrier has been removed in the first image carrier carrier removal section under the first condition stored in the condition storage section and second image transferred on the transfer medium, from which the carrier has been removed in the second image carrier carrier removal section under the first condition stored in the condition storage section; and a distance calculation section that calculates the distance between the first and second images detected by the optical sensor. 
         [0013]    In the image forming apparatus according to the present invention, the first and second image carrier carrier removal sections are rollers, and the rotation direction of the rollers differs between the first and second conditions. 
         [0014]    The image forming apparatus according to the present invention further includes a carrier removal section of a transfer medium that removes the carrier from the first and second images transferred on the transfer medium. 
         [0015]    The image forming apparatus according to the present invention further includes a second transfer medium carrier removal section that removes the carrier from the first image transferred on the transfer medium. 
         [0016]    The image forming apparatus according to the present invention further includes a second first image carrier carrier removal section that removes the carrier from the first image from which the carrier has been removed in the first image carrier carrier removal section; and a second second image carrier carrier removal section that removes the carrier from the second image from which the carrier has been removed in the second image carrier carrier removal section. 
         [0017]    In the image forming apparatus according to the present invention, the second first image carrier carrier removal section abuts and separates thereon from the first image carrier, and the second second image carrier carrier removal section abuts and separates thereon from the second image carrier. 
         [0018]    Further, according to a third aspect of the present invention, there is provided an image forming apparatus control method, including: charging a first image carrier by a first charging section; exposing the first image carrier charged by the first charging section by a first exposure section to form a latent image; developing the latent image formed on the first image carrier in the first exposure section using a first liquid developer containing a carrier and first toner particles by a first developing section; removing the carrier from a first image developed in the first developing section by a first image carrier carrier removal section; transferring the first image from which the carrier has been removed in the first image carrier carrier removal section onto a transfer medium by a first primary transfer section; charging a second image carrier by a second charging section; exposing the second image carrier charged by the second charging section by a second exposure section to form a latent image; developing the latent image formed on the second image carrier in the second exposure section using a second liquid developer containing the carrier and second toner particles by a second developing section; removing the carrier from a second image developed in the second developing section by a second image carrier carrier removal section; transferring the second image from which the carrier has been removed in the second image carrier carrier removal section onto a transfer medium by a second primary transfer means; and performing image formation on a first recording medium under a first condition in which the carrier removal amount in the first image carrier carrier removal section or second image carrier carrier removal section is set to a first carrier removal amount, while performing image formation on a second recording medium having a rougher surface than that of the first recording medium under a second condition in which the carrier removal amount in the first image carrier carrier removal section or second image carrier carrier removal section is set to a second carrier removal amount smaller than the first carrier removal amount. When detecting the first and second images transferred on the transfer member by an optical sensor and calculating the distance between the first and second images detected by the optical sensor, the first condition is used to perform image formation. 
         [0019]    In the image forming apparatus control method according to the present invention, the first and second image carrier carrier removal sections are rollers, and the rotation direction of the rollers differs between the first and second conditions. 
         [0020]    The image forming apparatus control method according to the present invention further includes removing the carrier from the first and second images transferred on the transfer medium by a second transfer medium carrier removal section. 
         [0021]    The image forming apparatus control method according to the present invention further including removing the carrier from the first image transferred on the transfer medium by a second transfer medium carrier removal section. 
         [0022]    The image forming apparatus control method according to the present invention further includes: removing the carrier from the first image from which the carrier has been removed in the first image carrier carrier removal section by a second first image carrier carrier removal section; and removing the carrier from the second image from which the carrier has been removed in the second image carrier carrier removal section by a second second image carrier carrier removal section. 
         [0023]    In the image forming apparatus control method according to the present invention, the second first image carrier carrier removal section abuts and separates thereon from the first image carrier, and the second second image carrier carrier removal section abuts and separates thereon from the second image carrier. 
         [0024]    According to the present invention, when the color shift compensation mode is executed, the removal amount of the carrier on the intermediate transfer belt is increased as compared to the removal amount in the normal printing operation, so that the position information of the resist marks can be accurately acquired without deterioration in the accuracy of the resist mark detection results obtained by the optical sensor, thereby achieving accurate color shift compensation. 
         [0025]    According to the present invention, when the carrier on the intermediate transfer member is removed in order to prevent deterioration in the accuracy of the resist mark detection results obtained by the optical sensor in the color shift compensation mode, the color shift compensation mode is executed under the same condition as in the image forming mode in terms of the carrier removal amount. This prevents deterioration in the cleaning performance when cleaning the resist marks transferred onto the intermediate transfer member by means of the intermediate transfer member cleaning blade. 
         [0026]    The following reference embodiment is also possible. That is, an image forming apparatus according to the present invention has: a plurality of image carriers, for respective colors, that carry developed images produced by using a liquid developer containing a carrier and toner particles; an intermediate transfer member that moves in a predetermined direction, onto which the developed images are transferred from the plurality of image carriers; and an optical sensor that detects the developed images transferred to predetermined positions on the intermediate transfer member. The image forming apparatus has a color shift compensation mode that transfers resist marks to predetermined positions on the intermediate transfer member by the plurality of image carriers, detects the resist marks by the optical sensor, calculates a color shift amount between different colors, and compensates the calculated color shift amount and a plurality of image forming modes having different conditions concerning at least the removal amount of the carrier on the intermediate transfer member. The color shift compensation mode is executed under a condition of the same carrier removal amount as in the image forming mode in which the removal amount of the carrier on the intermediate transfer member is largest of all the image forming modes provided in the image forming apparatus. 
         [0027]    In the image forming apparatus according to the reference embodiment of the present invention, the plurality of image forming modes are modes that form images on different types of recording media. 
         [0028]    The image forming apparatus according to the reference embodiment of the present invention has an intermediate transfer member squeezing roller arranged downstream relative to the plurality of image carriers and changes the peripheral rotation speed of the intermediate transfer member squeezing roller among the plurality of image forming modes to change a condition concerning the removal amount of the carrier on the intermediate transfer member. 
         [0029]    The image forming apparatus according to the reference embodiment of the present invention has a plurality of intermediate transfer member squeezing rollers arranged respectively downstream relative to the plurality of image carriers and changes the peripheral rotation speed of the intermediate transfer member squeezing rollers among the plurality of image forming modes to change a condition concerning the removal amount of the carrier on the intermediate transfer member. 
         [0030]    The image forming apparatus according to the reference embodiment of the present invention has a plurality of image carrier squeezing rollers abutting the plurality of image carriers respectively at the portions upstream relative to the nips between the intermediate transfer member and respective image carriers and changes the peripheral rotation speed of the image carrier squeezing rollers among the plurality of image forming modes to change a condition concerning the removal amount of the carrier on the intermediate transfer member. 
         [0031]    In the image forming apparatus according to the reference embodiment of the present invention, the plurality of image forming modes are modes in which toner consumption amount for use in an image forming process differs from one another. 
         [0032]    In the image forming apparatus according to the reference embodiment of the present invention, the moving speed of the intermediate transfer member is not changed among the plurality of image forming modes. 
         [0033]    Further, an image forming apparatus control method according to the reference embodiment of the present invention is a control method of an image forming apparatus having: a plurality of image carriers, for respective colors, that carry developed images produced by using a liquid developer containing a carrier and toner particles; an intermediate transfer member that moves in a predetermined direction, onto which the developed images are transferred from the plurality of image carriers; and an optical sensor that detects the developed images transferred to predetermined positions on the intermediate transfer member. The image forming apparatus control method includes a color shift compensation mode that transfers resist marks to predetermined positions on the intermediate transfer member by the plurality of image carriers, detects the resist marks by the optical sensor, calculates a color shift amount between different colors, and compensates the calculated color shift amount and a plurality of image forming modes having different conditions concerning at least the removal amount of the carrier on the intermediate transfer member. The color shift compensation mode is executed under a condition of the same carrier removal amount as in the image forming mode in which the removal amount of the carrier on the intermediate transfer member is largest of all the image forming modes provided in the image forming apparatus. 
         [0034]    According to the present invention, when the color shift compensation mode is executed, the removal amount of the carrier on the intermediate transfer belt is increased as compared to the removal amount in the normal printing operation, so that the position information of the resist marks can be accurately acquired without in the accuracy of deterioration of the resist mark detection results obtained by the optical sensor, thereby achieving accurate color shift compensation. 
         [0035]    According to the present invention, when the carrier on the intermediate transfer member is removed in order to prevent deterioration in the accuracy of the resist mark detection results obtained by the optical sensor in the color shift compensation mode, the color shift compensation mode is executed under the same condition as in the image forming mode in terms of the carrier removal amount. This prevents deterioration in the cleaning performance when cleaning the resist marks transferred onto the intermediate transfer member by means of the intermediate transfer member cleaning blade. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]      FIG. 1  is a view showing main components constituting an image forming apparatus according to a first embodiment of the present invention; 
           [0037]      FIG. 2  is a cross-sectional view showing main components of an image forming section and developing unit in the first embodiment of the present invention; 
           [0038]      FIGS. 3A and 3B  are views showing an intermediate transfer member squeezing unit of the image forming apparatus according to embodiments of the present invention; 
           [0039]      FIG. 4  is a view showing main components constituting an image forming apparatus according to a second embodiment of the present invention; 
           [0040]      FIG. 5  is a cross-sectional view showing main components of an image forming section and developing unit in the second embodiment of the present invention; 
           [0041]      FIG. 6  is a view showing main components constituting an image forming apparatus according to a fourth embodiment of the present invention; 
           [0042]      FIG. 7  is another view showing main components constituting an image forming apparatus according to the fourth embodiment of the present invention; 
           [0043]      FIG. 8  is a cross-sectional view showing main components of an image forming section and developing unit in the fourth embodiment of the present invention; 
           [0044]      FIGS. 9A and 9B  are views showing main components of a developing unit in the image forming apparatus according to a fifth embodiment of the present invention; 
           [0045]      FIGS. 10A and 10B  are another views showing main components of the developing unit in an image forming apparatus according to the fifth embodiment of the present invention; 
           [0046]      FIG. 11  is a view showing an example of resist marks formed onto an intermediate transfer member  40 ; 
           [0047]      FIG. 12  is a view showing a flowchart of color shift compensation mode processing; 
           [0048]      FIG. 13  is a view showing resist marks for sub-scanning direction resist displacement (skew amount) detection; 
           [0049]      FIG. 14  is a view showing resist marks for main-scanning direction resist displacement detection; 
           [0050]      FIG. 15  is a view showing a sensor output observed when resist marks are detected by means of an optical sensor  90 ; 
           [0051]      FIG. 16  is another view showing a sensor output observed when resist marks are detected by means of an optical sensor  90 ; and 
           [0052]      FIG. 17  is a view schematically showing a state where resist marks are detected by means of an optical sensor  90 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0053]    Embodiments of the present invention will be described below with reference to the accompanying drawings.  FIG. 1  is a view showing main components constituting an image forming apparatus according to a first embodiment of the present invention. An image forming apparatus of this embodiment has image forming sections of different colors that are arranged at a middle part of the apparatus. Developing units  30 Y,  30 M,  30 C and  30 K are arranged in the lower part of the image forming apparatus and intermediate transfer member  40  and a secondary transfer section (secondary transfer unit)  60  are arranged in the upper part of the apparatus. 
         [0054]    The image forming sections are formed respectively by image carriers  10 Y,  10 M,  10 C and  10 K, corona chargers  11 Y,  11 M,  11 C and  11 K and not shown exposure units  12 Y,  12 M,  12 C and  12 K. The exposure units  12 Y,  12 M  12 C and  12 K each have an optical system such as a semiconductor laser, a polygon mirror, an F-θ lens. The image carriers  10 Y,  10 M,  10 C and  10 K are uniformly electrically charged by the respective corona chargers  11 Y,  11 M,  11 C and  11 K and exposed to respective beams of light that are modulated respectively by input video signals by means of the exposure units  12 Y,  12 M,  12 C and  12 K to form electrostatic latent images on the electrically charged image carriers  10 Y,  10 M,  10 C and  10 K. The developing units  30 Y,  30 M,  30 C and  30 K each have developing rollers  20 Y,  20 M,  20 C and  20 K, developer reservoirs  31 Y,  31 M,  31 C and  31 K storing liquid developer of different colors of yellow (Y), magenta (M), cyan (C) and black (K), anilox rollers  32 Y,  32 M,  32 C and  32 K which are application rollers for applying the liquid developer of these colors from the developer reservoirs  31 Y,  31 M,  31 C and  31 K to the developing rollers  20 Y,  20 M,  20 C and  20 K, and the like and develop the electrostatic latent images formed on the image carriers  10 Y,  10 M,  10 C and  10 K by means of the liquid developer of the different colors. 
         [0055]    The intermediate transfer member  40  is an endless belt that is wound around a drive roller  41  and a tension roller  42  and is driven to rotate by the drive roller  41 , while it is brought into abutting the image carriers  10 Y,  10 M,  10 C and  10 K respectively at primary transfer sections  50 Y,  50 M,  50 C and  50 K. In the primary transfer sections  50 Y,  50 M,  50 C and  50 K, the image carriers  10 Y,  10 M,  10 C and  10 K are respectively arranged opposite to primary transfer rollers  51 Y,  51 M,  51 C and  51 K with the intermediate transfer member  40  interposed between them. The toner images of the different colors on the image carriers  10 Y,  10 M,  10 C and  10 K are sequentially transferred onto the intermediate transfer member  40  one on the other at the respective transfer positions that are the abutting positions between the intermediate transfer member  40  and the image carriers  10 Y,  10 M,  10 C and  10 K so as to form a full color toner image. 
         [0056]    In the secondary transfer unit  60 , a secondary transfer roller  61  is arranged opposite to a belt drive roller  41  with the intermediate transfer member  40  interposed between them. Further, a cleaning unit that includes a secondary transfer roller cleaning blade  62  is also arranged in the secondary transfer unit  60 . At the transfer position at which the secondary roller  61  is provided, a single color toner image or full color toner image formed on the intermediate transfer member  40  is transferred onto a recording medium such as a paper, a film or a cloth conveyed along a sheet member conveyance route L. 
         [0057]    A fixing unit  90  is arranged on the downstream side of the sheet member conveyance route L. The fixing unit  90  fixes the single color toner image or the full color toner image transferred onto the recording medium such as a paper by fusion. 
         [0058]    The tension roller  42  supports the intermediate transfer member  40  together with the belt drive roller  41 . A cleaning unit including an intermediate transfer member cleaning blade  46  is so arranged as to be brought into abutting the tension roller  42  at the location where the intermediate transfer member  40  is wound around the tension roller  42 . 
         [0059]    Now, the image forming sections and developing units will be described below.  FIG. 2  is a cross-sectional view showing main components of the image forming section and developing unit in the first embodiment of the present invention. Since the image forming sections and developing units of different colors respectively have the same configuration, the image forming section and the developing unit of Y (yellow) will be described below. 
         [0060]    In the image forming section, an image carrier cleaning roller  16 Y, an image carrier cleaning blade  18 Y, a corona charger  11 Y, an exposure unit  12 Y, a developing roller  20 Y of the developing unit  30 Y and an image carrier squeezing roller  13 Y are arranged along the outer periphery of the image carrier  10 Y in the mentioned order as viewed in the sense of rotation thereof. 
         [0061]    Reference numeral  17 Y denotes an image carrier cleaning roller cleaning blade for cleaning the image carrier cleaning roller  16 Y. Further, a cleaning unit including an image carrier squeezing roller cleaning blade  14 Y is provided for the image carrier squeezing roller  13 Y as an attachment configuration. 
         [0062]    Reference numeral  70 Y denotes a first image carrier developer collection section for receiving a liquid developer dropped from the image carrier squeezing roller cleaning blade  14 Y, and reference numeral  73 Y is a third image carrier developer collection section for receiving a liquid developer dropped from the image carrier cleaning roller cleaning blade  17 Y and image carrier cleaning blade  18 Y. A pipe for evacuating the liquid developer received from the blade is connected to the lower part of the first image carrier developer collection section  70 Y. Similarly, a pipe for evacuating the liquid developer received from the blade is connected to the lower part of the third image carrier developer collection section  73 Y. 
         [0063]    A developing roller cleaning blade  21 Y, an anilox roller  32 Y, and a toner compression corona generator  22 Y are arranged along the outer periphery of the developing roller  20 Y in the developing unit  30 Y. A restricting blade  33 Y for controlling the amount of a liquid developer supplied to the developing roller  20 Y is brought into abutting the anilox roller  32 Y. 
         [0064]    A reference numeral  72 Y denotes a developing roller developer collection section for receiving a liquid developer dropped from the developing roller cleaning blade  21 Y. A pipe for evacuating the liquid developer received from the blade is connected to the lower part of the developing roller developer collection section  72 Y. A liquid developer supply roller  34 Y is housed in the developer reservoir  31 Y. 
         [0065]    The primary transfer roller  51 Y of the primary transfer section is arranged at the position opposite to the image carrier  10 Y along the intermediate transfer member  40 . 
         [0066]      FIGS. 3A and 3B  are views showing an intermediate transfer member squeezing unit of the image forming apparatus according to embodiments of the present invention. The intermediate transfer member squeezing unit is configured to squeeze the intermediate transfer member  40  at the portion immediately downstream relative to the transfer nip of the image carrier  10 K. In the present embodiment, an intermediate transfer member squeezing unit  52 K including an intermediate transfer member squeezing roller  53 K, a backup roller  54 K, and an intermediate transfer member squeezing roller cleaning blade  55 K is arranged along the intermediate transfer member  40  at the portion downstream side relative to the developing unit  30 K in the moving direction of the intermediate transfer member  40 . 
         [0067]    Reference numeral  84 K is a first intermediate transfer member developer collection section for receiving a liquid developer dropped from the intermediate transfer member squeezing roller cleaning blade  55 K. A pipe for evacuating the liquid developer received from the blade is connected to the lower part of the first intermediate transfer member developer collection section  84 K. 
         [0068]    The image carrier  10 Y is a photosensitive drum that is a cylindrical member having a width broader than the width of the developing roller  20 Y and having a photosensitive layer formed on the outer peripheral surface thereof. The image carrier  10 Y rotates clockwise as shown in  FIG. 2 . The photosensitive layer of the image carrier  10 Y is typically formed by using an organic image carrier or an amorphous silicon image carrier. The corona charger  11 Y is arranged at the upstream side relative to the nip portion formed between the image carrier  10 Y and the developing roller  20 Y in the sense of rotation of the image carrier  10 Y. A voltage is applied from a power source (not shown) to corona charge the image carrier  10 Y. The exposure unit  12 Y is arranged at the downstream side relative to the corona charger  11 Y in the sense of rotation of the image carrier  10 Y to expose the electrically charged surface of the image carrier  10 Y to a laser light and form a latent image on the image carrier  10 Y. 
         [0069]    The components such as rollers arranged in the earlier stage in the image forming process are assumed to be located on the upstream relative to components such as rollers arranged in the later stage thereof. 
         [0070]    The developing unit  30 Y includes the toner compression corona generator  22 Y for exerting a compaction effect and developer reservoir  31 Y storing a liquid developer in which toner is dispersed in carrier liquid to a weight ratio of about 20%. 
         [0071]    Further, as described above, the developing unit  30 Y includes the development roller  20 Y bearing the liquid developer, anilox roller  32 Y that functions as an application roller for applying the liquid developer to the developing roller  20 Y, restricting blade  33 Y for resting the amount of the liquid developer to be applied to the developing roller  20 Y, supply roller  34  for supplying the liquid developer to the anilox roller  32 Y while agitating and conveying the liquid developer, toner compression corona generator  22 Y for making the liquid developer borne on the developing roller  20 Y in a compacted state, and developing roller cleaning blade  21 Y for cleaning the developing roller  20 Y. 
         [0072]    The liquid developer contained in the developer container  31 Y is not a popular volatile low concentration (about 1 to 2 wt %) and low viscosity liquid developer that is volatile at room temperature and prepared by using Isopar (trademark, available from Exxon) as carrier liquid but a non-volatile high concentration and high viscosity liquid developer that is not volatile at room temperature. More specifically, the liquid developer that is employed for the purpose of the present invention is a high viscosity (about 30 to 10,000 mPa·s) liquid developer prepared by adding solid particles of an average particle size of 1 μm, which are formed by dispersing a coloring agent such as a pigment in thermoplastic resin, in a liquid solvent such as an organic solvent, silicon oil, mineral oil or edible oil with a dispersing agent to make the toner solid concentration equal to about 20%. 
         [0073]    The anilox roller  32 Y functions as an application roller for supplying the liquid developer to the developing roller  20 Y and applying the liquid developer to the same. The anilox roller  32 Y is a cylindrical roller having an undulated surface produced by uniformly forming fine helical grooves so as to make it easily bear a liquid developer. The liquid developer is supplied from the developer reservoir  31 Y to the developing roller  20 Y by means of the anilox roller  32 Y. As shown in  FIG. 2 , when the apparatus is running, the supply roller  34 Y rotates clockwise to supply the liquid developer to the anilox roller  32 Y, and the anilox roller  32 Y rotates counterclockwise to apply the liquid developer to the developing roller  20 Y. 
         [0074]    The restricting blade  33 Y is an elastic blade having an elastic member arranged on the surface thereof. More specifically, the restricting blade  33 Y includes a rubber section that is typically made of urethan rubber and is brought into abutting the surface of the anilox roller  32 Y and a metal plate supporting the rubber section. The restricting blade  33 Y restricts and adjusts the film thickness and the amount of the liquid developer conveyed by the anilox roller  32 Y, and also adjusts the amount of the liquid developer to be supplied to the developing roller  20 Y. 
         [0075]    The developing roller  20 Y is a cylindrical member that is driven to rotate counterclockwise around the axis of rotation thereof as shown in  FIG. 2 . The developing roller  20 Y is formed by arranging an elastic layer typically made of polyurethane rubber, silicon rubber or NBR on the outer peripheral surface of an inner core, which is typically made of iron or some other metal. The developing roller cleaning blade  21 Y is typically made of rubber and brought into abutting the surface of the developing roller  20 Y. The developing roller cleaning blade  21 Y is arranged at the downstream side relative to the development nip where the developing roller  20 Y is brought into abutting the image carrier  10 Y in the sense of rotation of the developing roller  20 Y so as to scrape off and remove the liquid developer remaining on the developing roller  20 Y. 
         [0076]    The toner compression corona generator  22 Y is an electric field application means for increasing a charged bias on the surface of the developing roller  20 Y. The liquid developer conveyed by the developing roller  20 Y is subjected to the application of an electric field by the toner compression corona generator  22 Y at toner compression site in the direction from the toner compression corona generator  22 Y toward the developing roller  20 Y, as shown in  FIG. 2 . 
         [0077]    As the electric field application means for toner compression, a compaction roller may be used in place of the corona discharger shown in  FIG. 2  producing corona discharge. Such a compaction roller may be a cylindrical member and formed as an elastic roller by covering the surface thereof with an elastic material like the developing roller  20  Y. More specifically, the compaction roller may have a structure provided with a conductive resin layer or rubber layer is on an surface layer of a metal roller base material, and rotate in the clockwise direction opposite to the rotation direction of the developing roller  20 Y. 
         [0078]    The developer carried and toner-compressed by the developing roller  20 Y is applied with an electric field at the development nip where the developing roller  20 Y is brought into abutting the image carrier  10 Y so as to be developed according to the latent image on the image carrier  10 Y. The residual developer remaining on the development roller  20 Y is scraped off and removed by the developing roller cleaning blade  21 Y and dropped to the developing roller developer collection section  72 Y so as to be reused. Note that the carrier liquid and the toner dropped to the developing roller developer collection section  72 Y are not in a mixed color state. 
         [0079]    An image carrier squeezing unit on the upstream side relative to the primary transfer is located on the downstream side relative to the developing device  20 Y, opposed to the image carrier member  10 Y, and collects the residual developer that is produced after the toner image on the image carrier  10 Y is developed. The image carrier squeezing unit includes the image carrier squeezing roller  13 Y constituted by an elastic roller member which has a surface covered with an elastic member and is brought into sliding contact with the image carrier  10 Y so as to be driven to rotate and image carrier squeezing roller cleaning blade  14 Y pressed against and brought into sliding contact with the image carrier squeezing roller  13 Y to clean the surface thereof. The image carrier squeezing unit has a function of collecting the surplus carrier liquid and the unnecessary fogging toner from the developer of the image developed on the image carrier  10 Y to raise the toner particle content ratio in the developed visible image. 
         [0080]    In the primary transfer section  50 Y, the developer image developed on the image carrier  10 Y is transferred onto the intermediate transfer member  40  by the primary transfer roller  51 Y. In this process, the image carrier  10 Y and the intermediate transfer member  40  are configured to move at an equal speed, so that load caused by rotation and motion thereof is reduced and disturbance on the visualized toner image on the image carrier  10 Y is suppressed. 
         [0081]    A cleaning unit on the downstream side of the primary transfer is located on the downstream side relative to the primary transfer section  50 Y, opposed to the image carrier member  10 Y, and collects the residual liquid developer on the image carrier member  10 Y before an electrostatic latent image is formed. The cleaning unit includes, as shown in  FIG. 2 , the image carrier cleaning roller  16 Y constituted by an elastic roller member which has a surface covered with an elastic member and is brought into sliding contact with the image carrier  10 Y so as to be driven to rotate and image carrier cleaning roller cleaning blade  17 Y pressed against and brought into sliding contact with the image carrier squeezing roller  16 Y to clean the surface thereof. The cleaning unit has a function of collecting the surplus carrier liquid and the unnecessary toner that has not been transferred. The image carrier cleaning roller  16 Y has a structure in which a rubber layer is arranged on the surface of a metal roller base material and is applied with a bias voltage that attracts toner particles on the image carrier  11 . The image carrier cleaning roller  16 Y is provided mainly for the purpose of cleaning a toner particle component contained in the residual liquid developer. 
         [0082]    The image carrier cleaning blade  18 Y configured to perfectly clean the surface of the image carrier  10 Y before a new electrostatic latent image is formed is arranged on the downstream side relative to the image carrier cleaning roller  16 Y. The image carrier cleaning blade  18 Y is provided mainly for the purpose of cleaning a carrier component contained in the residual liquid developer. 
         [0083]    The intermediate transfer member squeezing unit  52 K is arranged at the downstream side relative to the primary transfer section  50 K to remove the surplus carrier liquid on the intermediate transfer member  40  and raise the toner particle content ratio in the developed visible image. In practicing the present invention, such a squeezing unit may be arranged at an arbitrary location upstream relative to a detection section of an optical sensor  90 . 
         [0084]    Like the image carrier squeezing units, the intermediate transfer member squeezing unit  52 K includes an intermediate transfer member squeezing roller  53 K which is an elastic roller member having an elastic member arranged on the surface thereof and brought into sliding contact with the intermediate transfer member  40  so as to be driven to rotate, a backup roller  54 K arranged opposite to the intermediate transfer member squeezing roller  53 K with the intermediate transfer member  40  interposed between them, a cleaning blade  55 K pressed against and brought into sliding contact with intermediate transfer member squeezing roller  53 K to collect the surplus carrier and unnecessary fogging toner from the developer primary-transferred onto the intermediate transfer member  40 . 
         [0085]    Next, the flow of the liquid developer in the image forming apparatus according to the present invention will be described with reference to  FIGS. 1 and 2 . The secondary transfer roller  61  is arranged opposite to the belt drive roller  41  with the intermediate transfer member  40  interposed between them. Further, the cleaning unit including the secondary transfer roller cleaning blade  62  is also arranged for the secondary transfer roller  61 . 
         [0086]    Reference numeral  63  is a secondary transfer roller developer collection section for receiving the liquid developer dropped from the secondary roller cleaning blade  62 . A pipe for evacuating the liquid developer received from the blade is connected to the lower part of the secondary transfer roller developer collection section  63 . This pipe communicates with a first waste tank  440 . The liquid developer scraped off by the secondary transfer roller cleaning blade  62  is a liquid developer in which toners of different colors are mixed, so that the liquid developer collected in the secondary transfer roller developer collection section  63  is discharged to the first waste tank  440  through the pipe. 
         [0087]    Reference numeral  47  is a secondary intermediate transfer member developer collection section for receiving the liquid developer dropped from the intermediate transfer member cleaning blade  46 . A pipe for evacuating the liquid developer received from the blade is connected to the lower part of the secondary intermediate transfer member developer collection section  47 . This pipe communicates with a second waste tank  441 . The liquid developer scraped off by the intermediate transfer member cleaning blade  46  is a liquid developer in which toners of different colors are mixed, so that the liquid developer collected in the secondary intermediate transfer member developer collection section  47  is discharged to the second waste tank  440  through the pipe. 
         [0088]    In  FIG. 1 , reference numerals  400 Y,  400 M,  400 C, and  400 K denote agitation tanks,  401 Y,  401 M,  401 C, and  401 K denote developer supply tanks,  402 Y,  402 M,  402 C, and  402 K denote buffer tanks,  410  denotes a carrier tank,  450 Y,  450 M,  450 C, and  450 K denote first pumps,  451 Y,  451 M,  451 C, and  451 K denote second pumps,  452 Y,  452 M,  452 C, and  452 K denote third pumps, and  453 Y,  453 M,  453 C, and  453 K denote fourth pumps. The lines connecting among the reservoirs, collection sections, tanks, and pumps schematically denote the pipes. 
         [0089]    The agitation tanks  400 Y,  400 M,  400 C, and  400 K are tanks for preparing a liquid developer having a toner solid concentration of about 20% to be supplied to the developer reservoirs  31 Y,  31 M,  31 C, and  31 K. 
         [0090]    The developer supply tanks  401 Y,  401 M,  401 C, and  401 K are tanks for storing a high concentration toner having a toner solid concentration of 20% or more. The carrier tank  410 , which is a tank for storing a carrier stock solution, is piped to the agitation tanks  400 Y,  400 M,  400 C, and  400 K of respective colors through the fourth pumps  453 Y,  453 M,  453 C, and  453 K. 
         [0091]    The agitation tanks  400 Y,  400 M,  400 C, and  400 K receive supply of high concentration toners from the developer supply tanks  401 Y,  401 M,  401 C, and  401 K. To this end, the second pumps  451 Y,  451 M,  451 C, and  451 K are driven. 
         [0092]    The agitation tanks  400 Y,  400 M,  400 C, and  400 K also receive supply of a carrier stock solution from the carrier tank  410  by means of the drive of the fourth pumps  453 Y,  453 M,  453 C, and  453 K. 
         [0093]    The agitation tanks  400 Y,  400 M,  400 C, and  400 K are each provided with toner concentration detection means (not shown) such as an optical sensor. The agitation tanks  400 Y,  400 M,  400 C, and  400 K use the toner concentration detection means to detect the concentration and perform on/off control of the respective pumps using a not shown controller so as to maintain appropriate concentration of the liquid developer in the agitation tanks  400 Y,  400 M,  400 C, and  400 K. Further, the agitation tanks  400 Y,  400 M,  400 C, and  400 K are each provided with not shown agitation units and uniformly agitate the developer therein by driving the agitation units. 
         [0094]    During the operating time of the apparatus, adequate amount of liquid developer is always supplied from the agitation tanks  400 Y,  400 M,  400 C, and  400 K to the developer reservoirs  31 Y,  31 M,  31 C, and  31 K by means of the first pumps  450 Y,  450 M,  450 C, and  450 K. 
         [0095]    The liquid developer collected in the first image carrier developer collection sections  70 Y,  70 M,  70 C, and  70 K and developing roller developer collection section  72 Y,  72 M,  72 C, and  72 K is introduced into the agitation tanks  400 Y,  400 M,  400 C, and  400 K through the pipes so as to be reused. 
         [0096]    The liquid developer collected in the third image carrier developer collection sections  73 Y,  73 M,  73 C, and  73 K is introduced into the buffer tanks  402 Y,  402 M,  402 C, and  402 K through the pipes for temporary storage. The liquid developer in the buffer tanks  402 Y,  402 M,  402 C, and  402 K is fed to the agitation tanks  400 Y,  400 M,  400 C, and  400 K by the operation of the second pumps  451 Y,  451 M,  451 C, and  451 K. The reason that the second pumps  451 Y,  451 M,  451 C, and  451 K are used here is that the solid concentration of the liquid developer collected in the third image carrier developer collection sections  73 Y,  73 M,  73 C, and  73 K is high. 
         [0097]    The liquid developer collected in the developer collection sections of respective color units has not been subjected to color superposition and therefore are not in a mixed color state, so that it is to be reused. On the other hand, the liquid developer collected in the first intermediate transfer member developer collection section  84 K is a liquid developer in which toners of different colors are mixed, so that the liquid developer collected in the first intermediate transfer member developer collection section  84 K is discharged to the second waste tank  441  through the pipe. 
         [0098]    Next, a determination means for realizing a plurality of modes in which images are formed in different types of recording media will be described. The image forming apparatus according to the present invention has a plurality of image forming modes by which images can be printed on different types of papers (art paper, coated paper, high-quality paper, regular paper, etc.). 
         [0099]    The reason that the plurality of image forming modes corresponding to the paper types are required is that the amount of the carrier required in an image forming process differs depending on the paper type. The image forming apparatus according to the present invention has two image forming modes for a first type recording medium, typified by art paper, coated paper, etc., having a comparatively smooth surface on which there is little unevenness as viewed microscopically and a second type recording medium, typified by high-quality paper, regular paper, etc., having a comparatively rough surface on which there is much unevenness as viewed microscopically. 
         [0100]    In order to achieve a transfer process including primary and secondary transfer using a liquid developer, a sufficient amount of a carrier is required to electrophorese the toner. Therefore, the amount of a carrier required for the first type recording medium having a surface on which there is little unevenness is small, and amount of a carrier required for the second type recording medium having a surface on which there is much unevenness is larger than the case of the first type recording medium. 
         [0101]    In the present embodiment, a paper type determination sensor  5  as shown in  FIG. 1  is provided for detecting the type of a recording medium. The paper type determination sensor  5  is constituted by a light-emitting element  6  that irradiates a recording medium conveyed along the conveyance route with a light and a light receiving element  7  that detects reflection of the reflected light from the recording medium. In the present embodiment, a signal such as reflectance of the reflected light is input from the light-receiving element  7  to a not shown controller such as a CPU, where the type (art paper, coated paper, high-quality paper, regular paper, etc.) of the recording medium is determined. 
         [0102]    Next, a color shift compensation mode in the present invention will be described. There exists a problem of color shift in the image forming apparatus according to the present invention that performs image formation using developing units  30 Y,  30 M,  30 C, and  30 K of four colors. That is, when toner images respectively formed by the different developing units  30 Y,  30 M,  30 C, and  30 K are transferred onto the intermediate transfer member  40 , the transfer positions are shifted from one another, which appears as a change in the color tone on a recording medium. 
         [0103]    To eliminate this problem, the image formation apparatus has a color shift compensation mode. In this color shift compensation mode, reference pattern images (hereinafter, referred to as “resist marks”) for detecting color shift, which are previously formed on the intermediate transfer member  40 , are detected using the optical sensor  90  to acquire position information of the resist marks, and positioning (color shift compensation processing, displacement compensation processing) of respective toner images are performed based on the acquired position information. 
         [0104]    The optical sensor  90  for detecting the resist marks are provided at the preceding stage of the transfer nip of the secondary transfer unit  60  as shown in  FIG. 1 . As the optical sensor  90 , a known device such as a light-emitting and light-receiving element pair or CCD camera can be used. 
         [0105]    As shown in  FIG. 11 , in this color shift compensation mode, resist marks YRM (yellow resist mark), MRM (magenta resist mark), CRM (cyan resist mark), and KRM (black resist mark) are formed, as toner images, in this order onto the intermediate transfer member  40  through the image forming process executed immediately after power-on. 
         [0106]    The resist marks thus formed are detected by the optical sensor  90 , and color shift amount between different colors is calculated by a not shown calculation means. In the color shift compensation mode, the image forming apparatus is controlled such that the color shift amount calculated by the calculation means is compensated by a known means. 
         [0107]    A toner image containing the carrier liquid on the intermediate transfer member  40  has high specularity, which may cause the resist marks to erroneously be detected by the optical sensor  90 . That is, at the color shift compensation processing time in a wet-developing image forming apparatus, resist mark detection results obtained by the optical sensor  90  may degrade in accuracy, with the result that accurate position information of the resist marks cannot be obtained, thus preventing accurate color shift compensation. 
         [0108]    In order to cope with this problem, a method can be considered in which the carrier liquid on the intermediate transfer member  40  is removed at the color shift compensation processing time. However, when the carrier liquid on the intermediate transfer member  40  is removed, solid content ratio in the resist marks is increased. When the resist marks on the intermediate transfer member  40  proceed in the process downstream and pass through the secondary transfer unit  60 , the solid content ratio in the resist marks are further increased. Then, there arises a new problem that cleaning performance when cleaning the resist marks transferred onto the intermediate transfer member  40  by means of the intermediate transfer member cleaning blade  46  is deteriorated. 
         [0109]    In view of this, at execution time of the color shift compensation mode in the present invention, the carrier contained in the resist marks is removed while the removal amount thereof is controlled so as not to be excessive. More specifically, the color shift compensation mode in the present invention is executed under a condition of the same carrier removal amount as in the image forming mode in which the removal amount of the carrier on the intermediate transfer member  40  is largest of all the image forming modes provided in the image forming apparatus. 
         [0110]    Thus, as described above, when the carrier on the intermediate transfer member  40  is removed in order to prevent deterioration in the accuracy of the resist mark detection results obtained by the optical sensor  90  in the color shift compensation mode, the color shift compensation mode is executed under the same condition as in the image forming mode in terms of the carrier removal amount. This prevents deterioration in the cleaning performance when cleaning the resist marks transferred onto the intermediate transfer member  40  by means of the intermediate transfer member cleaning blade. That is, according to the present invention, there can be provided an image forming apparatus capable of achieving both the prevention of deterioration in the resist mark detection accuracy and prevention of deterioration in the cleaning performance with respect to the intermediate transfer member in a balanced manner. 
         [0111]    An example of a plurality of image forming modes provided in an image forming apparatus includes those by which images can be formed on different types of papers. The image forming apparatus according to the present invention has two image forming modes: a mode (first type recording medium image forming mode) for image forming on a first type recording medium (art paper and coated paper) having a surface on which there is comparatively little unevenness and a mode (second type recording medium image forming mode) for image forming on a second type recording medium (high-quality paper and regular paper) having a surface on which there is comparatively much unevenness. The amount of a carrier required in the first type recording medium image forming mode is controlled to be small, and amount of a carrier required in the second type recording medium image forming mode is controlled to be larger than the first type recording medium image forming mode. In the first embodiment, the color shift compensation mode is executed under a condition (first condition) of the same carrier removal amount as in the first type recording medium image forming mode. 
         [0112]    When the second type recording medium image forming mode is executed, the intermediate transfer member squeezing roller  53 K of the intermediate transfer member squeezing unit is controlled to be rotated at the same peripheral rotation speed as the moving speed of the intermediate transfer member  40 . On the other hand, in the first type recording medium forming mode, the intermediate transfer member squeezing roller  53 K is controlled to be rotated at a peripheral rotation speed higher than the moving speed of the intermediate transfer member  40  to increase the amount of the carrier on the intermediate transfer member  40  to be removed by the intermediate transfer member squeezing roller  53 K as compared to the removal amount in the second type recording medium image forming mode so as to achieve an optimum condition for image forming on a recording medium such as art paper or coated paper. In the present embodiment, the same carrier removal condition (this carrier removal condition is referred to as “first condition”) as in this first type recording medium image forming mode is applied to the color shift compensation mode (note that the carrier removal condition in the second type recording medium image forming mode is referred to as “second condition”). 
         [0113]    An example of conditions at the execution time of the first and second type recording medium image forming modes in the first embodiment of the present invention is shown in the following Table 1. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                   
                 Second type 
               
               
                   
                 First type 
                 recording medium 
               
             
          
           
               
                   
                 recording medium 
                 High- 
                   
               
             
          
           
               
                   
                 Art 
                 Coated 
                 quality 
                 Regular 
               
               
                   
                 paper 
                 paper 
                 paper 
                 paper 
               
               
                   
                   
               
             
          
           
               
                 Peripheral speed 
                 210 
                 200 
               
               
                 of intermediate transfer member 
               
               
                 squeezing roller [mm/s] 
               
               
                 Solid content ratio 
                 40 
                 35 
               
               
                 on intermediate transfer member 
               
               
                 observed at position of optical 
               
               
                 sensor 90 [%] 
               
               
                   
               
             
          
         
       
     
         [0114]    Another example of the operation of the intermediate transfer member squeezing unit will be described below.  FIG. 3A  shows a state of the intermediate transfer member squeezing unit at the execution time of the second type recording medium image forming mode, and  FIG. 3B  shows a state of the intermediate transfer member squeezing unit at the execution time of the first type recording medium image forming mode. As shown in  FIGS. 3A and 3B , a configuration may be adopted in which, in the second type recording medium image forming mode, the intermediate transfer member squeezing roller  53 K is controlled to be rotated in the same direction as the moving direction of the intermediate transfer member  40  at the nip portion, while in the first type recording medium image forming mode, the intermediate transfer member squeezing roller  53 K is controlled to be rotated in the reverse direction to the moving direction of the intermediate transfer member  40  at the nip portion so as to increase the amount of the carrier on the intermediate transfer member  40  to be removed by the intermediate transfer member squeezing roller  53 K as compared to the removal amount in the second type recording medium image forming mode. In the present embodiment, the same carrier removal condition as in such a first type recording medium image forming mode may be applied to the color shift compensation mode. 
         [0115]    The conditions for the operation of the squeezing unit and other components at the execution time of the first type recording medium image forming mode, second type recording medium image forming mode, and color shift compensation mode are stored in a not shown storage means, and when each of the above modes is executed, a corresponding condition stored in the storage means is applied. Such a configuration is applied to all embodiments of the present invention. 
         [0116]    Further, in the first type recording medium image forming mode, the intermediate transfer member squeezing roller  53 K may be controlled to be rotated at a peripheral rotation speed higher than the moving speed of the intermediate transfer member  40  in the reverse direction to the moving direction of the intermediate transfer member  40  at the nip portion. The same carrier removal condition as in such a first type recording medium image forming mode may be applied to the color shift compensation mode. 
         [0117]    In the example shown in  FIG. 3B , the intermediate transfer member squeezing roller  53 K is rotated in the reverse direction to the moving direction of the intermediate transfer member  40 , so that the resist marks formed on the intermediate transfer member  40  may be disturbed. Thus, in the color shift compensation mode, a bias voltage for pressing the toner in the resist marks from the intermediate transfer member squeezing roller  53 K to the intermediate transfer member  40  is preferably applied. 
         [0118]    As described above, according to the first embodiment of the present invention, since the color shift compensation mode is executed under the same condition as in the first type recording medium image forming mode in which the removal amount of the carrier on the intermediate transfer member  40  is increased as compared to the removal amount in the second type recording medium image forming mode, the position information of the resist marks can be accurately acquired without deterioration in the accuracy of the resist mark detection results obtained by the optical sensor, thereby achieving accurate color shift compensation. Further, since the color shift compensation mode is executed under the same condition as in the image forming mode provided in the image forming apparatus in terms of the removal amount of the carrier on the intermediate transfer member  40 , it is possible to prevent deterioration in the cleaning performance of the cleaning blade for cleaning the resist marks transferred onto the intermediate transfer medium  40 . That is, according to the present invention, there can be provided an image forming apparatus capable of achieving both the prevention of deterioration in the resist mark detection accuracy and prevention of deterioration in the cleaning performance with respect to the intermediate transfer member in a balanced manner. 
         [0119]    Next, a second embodiment of the present invention will be described.  FIG. 4  is a view showing main components constituting an image forming apparatus according to the second embodiment of the present invention, and  FIG. 5  is a cross-sectional view showing main components of an image forming section and developing unit in the second embodiment of the present invention. 
         [0120]    In the first embodiment, the intermediate transfer member squeezing unit is provided only at the portion immediately downstream relative to the transfer nip of the image carrier  10 K, while in the second embodiment, four intermediate transfer member squeezing units are provided at the portions immediately downstream relative to respective transfer nips of the image carriers  10 Y,  10 M,  10 C, and  10 K. 
         [0121]    With reference to  FIG. 5 , the intermediate transfer member squeezing units will be described by taking the intermediate transfer member squeezing unit provided at the portion immediately downstream relative to the transfer nip of the image carrier  10 Y as an example. Since the intermediate transfer member squeezing units provided for the developing units of other colors have the same configuration, only the intermediate transfer member squeezing unit provided for the developing unit of yellow will be described below. 
         [0122]    The intermediate transfer member squeezing unit (in this case, for developing unit of yellow color) according to the second embodiment squeezes the intermediate transfer member  40  at the portion immediately downstream relative to the transfer nip of the image carrier  10 Y. In the present embodiment, an intermediate transfer member squeezing unit  52 Y constituted by an intermediate transfer member squeezing roller  53 Y, a backup roller  54 Y, an intermediate transfer member squeezing roller cleaning blade  55 Y is arranged on the downstream side relative to the developing unit  30 Y in the moving direction of the intermediate transfer member  40 . 
         [0123]    Reference numeral  84 Y is a first intermediate transfer member developer collection section for receiving a liquid developer dropped from the intermediate transfer member squeezing roller cleaning blade  55 Y. A pipe for evacuating the liquid developer received from the blade is connected to the lower part of the first intermediate transfer member developer collection section  84 Y. The liquid developer collected in the first intermediate transfer member developer collection section  84 Y is a liquid developer in which toners of different colors are mixed, so that the liquid developer collected in first intermediate transfer member developer collection section  84 Y is discharged to the second waste tank  441  through the pipe and is not reused. 
         [0124]    In the second embodiment, the intermediate transfer member squeezing units  52 Y,  52 M,  52 C, and  52 K are used to switch the carrier removal condition between the first and second type recording medium image forming modes. 
         [0125]    Also in the second embodiment, the color shift compensation mode is executed under the condition in which the removal amount of the carrier on the intermediate transfer member  40  is increased as compared to the removal amount in the second type recording medium image forming mode. As the concrete condition in this case, the same condition set in the first type recording medium image forming mode is adopted. 
         [0126]    In the image forming apparatus according to the second embodiment of the present invention, when executing the color shift compensation mode, the intermediate transfer member squeezing units  52 Y,  52 M,  52 C, and  52 K provided immediately downstream relative to the primary transfer nips of the image carriers of respective colors are used to remove a larger amount of carrier than in the second type recording medium image forming mode. In the present embodiment, the same carrier removal condition as in this first type recording medium forming mode is applied to the color shift compensation mode. 
         [0127]    When the second type recording medium image forming mode is executed, the intermediate transfer member squeezing rollers  53 Y,  53 M,  53 C, and  53 K of the intermediate transfer member squeezing units  52 Y,  52 M,  52 C, and  52 K are controlled to be rotated at the same peripheral rotation speed as the moving speed of the intermediate transfer member  40 . On the other hand, in the first type recording medium forming mode, the intermediate transfer member squeezing rollers  53 Y,  53 M,  53 C, and  53 K are controlled to be rotated at a peripheral rotation speed higher than the moving speed of the intermediate transfer member  40  to increase the amount of the carrier on the intermediate transfer member  40  to be removed by the intermediate transfer member squeezing rollers  53 Y,  53 M,  53 C, and  53 K as compared to the removal amount in the second type recording medium image forming mode. The same carrier removal condition as in this first type recording medium image forming mode is applied to the color shift compensation mode. 
         [0128]    An example of conditions at the execution time of the first and second type recording medium image forming modes in the second embodiment is shown in the following Table 2. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                   
                 Second type 
               
               
                   
                 First type 
                 recording medium 
               
             
          
           
               
                   
                 recording medium 
                 High- 
                   
               
             
          
           
               
                   
                 Art 
                 Coated 
                 quality 
                 Regular 
               
               
                   
                 paper 
                 paper 
                 paper 
                 paper 
               
               
                   
                   
               
             
          
           
               
                 Peripheral speed 
                 205 
                 200 
               
               
                 of intermediate transfer member 
               
               
                 squeezing roller [mm/s] 
               
               
                 Solid content ratio 
                 40 
                 35 
               
               
                 on intermediate transfer member 
               
               
                 observed at position of optical 
               
               
                 sensor 90 [%] 
               
               
                   
               
             
          
         
       
     
         [0129]    Although not shown, a configuration may be adopted in which, in the second type recording medium image forming mode, the intermediate transfer member squeezing rollers  53 Y,  53 M,  53 C, and  53 K are controlled to be rotated in the same direction as the moving direction of the intermediate transfer member  40  at the respective nip portions, while in the first type recording medium image forming mode, the intermediate transfer member squeezing rollers  53 Y,  53 M,  53 C, and  53 K are controlled to be rotated in the reverse direction to the moving direction of the intermediate transfer member  40  at the respective nip portions so as to increase the amount of the carrier on the intermediate transfer member  40  to be removed by the intermediate transfer member squeezing rollers  53 Y,  53 M,  53 C, and  53 K as compared to the removal amount in the second type recording medium image forming mode. The same carrier removal condition as in such a first type recording medium image forming mode may be applied to the color shift compensation mode. 
         [0130]    Further, in the first type recording medium image forming mode, the intermediate transfer member squeezing rollers  53 Y,  53 M,  53 C, and  53 K may be controlled to be rotated at a peripheral rotation speed higher than the moving speed of the intermediate transfer member  40  in the reverse direction to the moving direction of the intermediate transfer member  40  at the respective nip portions. The same carrier removal condition as in such a first type recording medium image forming mode may be applied to the color shift compensation mode. 
         [0131]    In the above cases, the intermediate transfer member squeezing rollers  53 Y,  53 M,  53 C, and  53 K are rotated in the reverse direction to the moving direction of the intermediate transfer member  40 , so that the resist marks formed on the intermediate transfer member  40  may be disturbed. Thus, in the color shift compensation mode, a bias voltage for pressing the toner in the resist marks from the intermediate transfer member squeezing rollers  53 Y,  53 M,  53 C, and  53 K to the intermediate transfer member  40  is preferably applied. 
         [0132]    As described above, according to the second embodiment of the present invention, since the color shift compensation mode is executed under the same condition as in the first type recording medium image forming mode in which the removal amount of the carrier on the intermediate transfer member  40  is increased as compared to the removal amount in the second type recording medium image forming mode, the position information of the resist marks can be accurately acquired without deterioration in the accuracy of the resist mark detection results obtained by the optical sensor, thereby achieving accurate color shift compensation. Further, since the color shift compensation mode is executed under the same condition as in the image forming mode provided in the image forming apparatus in terms of the removal amount of the carrier on the intermediate transfer member  40 , it is possible to prevent deterioration in the cleaning performance of the cleaning blade for cleaning the resist marks transferred onto the intermediate transfer medium  40 . 
         [0133]    Next, a third embodiment of the present invention will be described. The third embodiment can be practiced by the same configuration as those of the first and second embodiments. Also in the third embodiment, at the execution time of the first type recording medium image forming mode, the removal amount of the carrier on the intermediate transfer member  40  is increased as compared to the removal amount in the second type recording medium image forming mode. To this end, in the third embodiment, when executing the first type recording medium image forming mode, the image carrier squeezing rollers  13 Y,  13 M,  13 C, and  13 K provided immediately upstream relative to the primary transfer nips of the image carriers of respective colors are used to remove a larger amount of carrier than in the second type recording medium image forming mode and thus to increase the removal amount of the carrier on the intermediate transfer member  40 . The same carrier removal condition as in this first type recording medium forming mode may be applied to the color shift compensation mode. 
         [0134]    An example of conditions at the execution time of the first and second type recording medium image forming modes set for practicing the third embodiment using the configuration of  FIG. 1  is shown in the following Table 3. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 3 
               
             
             
               
                   
                   
               
               
                   
                   
                 Second type 
               
               
                   
                 First type 
                 recording medium 
               
             
          
           
               
                   
                 recording medium 
                 High- 
                   
               
             
          
           
               
                   
                 Art 
                 Coated 
                 quality 
                 Regular 
               
               
                   
                 paper 
                 paper 
                 paper 
                 paper 
               
               
                   
                   
               
             
          
           
               
                 Peripheral speed 
                 205 
                 200 
               
               
                 of image carrier 
               
               
                 squeezing roller [mm/s] 
               
               
                 Solid content ratio 
                 40 
                 35 
               
               
                 on intermediate transfer member 
               
               
                 observed at position of optical 
               
               
                 sensor 90 [%] 
               
               
                   
               
             
          
         
       
     
         [0135]    An example of conditions at the execution time of the first and second type recording medium image forming modes set for practicing the third embodiment using the configuration of  FIG. 4  is shown in the following Table 4. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 4 
               
             
             
               
                   
                   
               
               
                   
                   
                 Second type 
               
               
                   
                 First type 
                 recording medium 
               
             
          
           
               
                   
                 recording medium 
                 High- 
                   
               
             
          
           
               
                   
                 Art 
                 Coated 
                 quality 
                 Regular 
               
               
                   
                 paper 
                 paper 
                 paper 
                 paper 
               
               
                   
                   
               
             
          
           
               
                 Peripheral speed 
                 202 
                 200 
               
               
                 of image carrier 
               
               
                 squeezing roller [mm/s] 
               
               
                 Solid content ratio 
                 40 
                 35 
               
               
                 on intermediate transfer member 
               
               
                 observed at position of optical 
               
               
                 sensor 90 [%] 
               
               
                   
               
             
          
         
       
     
         [0136]    In the second type recording medium image forming mode, the image carrier squeezing rollers  13 Y,  13 M,  13 C, and  13 K are controlled to be rotated at the same peripheral rotation speed as that of the image carriers  10 Y  10 M,  10 C, and  10 K. On the other hand, in the first type recording medium image forming mode, the image carrier squeezing rollers  13 Y,  13 M,  13 C, and  13 K are controlled to be rotated at a peripheral rotation speed higher than that of the image carriers  10 Y,  10 M,  10 C, and  10 K so as to increase the removal amount of the carrier on the image carriers  10 Y,  10 M,  10 C, and  10 K and thus to increase the removal amount of the carrier on the intermediate transfer member  40  as compared to the removal amount in the second type recording medium image forming mode. The same carrier removal condition as in this first type recording medium image forming mode may be applied to the color shift compensation mode. 
         [0137]    Although not shown, a configuration may be adopted in which, in the second type recording medium image forming mode, the image carrier squeezing rollers  13 Y,  13 M,  13 C, and  13 K are controlled to be rotated in the same direction as the rotation direction of the image carriers  10 Y,  10 M,  10 C, and  10 K at the respective nip portions, while in the first type recording medium image forming mode, the image carrier squeezing rollers  13 Y,  13 M,  13 C, and  13 K are controlled to be rotated in the reverse direction to the rotation direction of the image carriers  10 Y,  10 M,  10 C, and  10 K at the respective nip portions so as to increase the removal amount of the carrier on the image carriers  10 Y,  10 M,  10 C, and  10 K and thus to increase the removal amount of the carrier on the intermediate transfer member  40  as compared to the removal amount in the second type recording medium image forming mode. The same carrier removal condition as in this first type recording medium image forming mode may be applied to the color shift compensation mode. 
         [0138]    Further, in the first type recording medium image forming mode, the image carrier squeezing rollers  13 Y,  13 M,  13 C, and  13 K may be controlled to be rotated at a peripheral rotation speed higher than the rotation speed of the image carriers  10 Y,  10 M,  10 C, and  10 K in the reverse direction to the rotation direction of the image carriers  10 Y,  10 M,  10 C, and  10 K at the respective nip portions. The same carrier removal condition as in such a first type recording medium image forming mode may be applied to the color shift compensation mode. 
         [0139]    As described above, according to the third embodiment of the present invention, since the color shift compensation mode is executed under the same condition as in the first type recording medium image forming mode in which the removal amount of the carrier on the intermediate transfer member  40  is increased as compared to the removal amount in the second type recording medium image forming mode, the position information of the resist marks can be accurately acquired without deterioration in the accuracy of the resist mark detection results obtained by the optical sensor, thereby achieving accurate color shift compensation. Further, in the present embodiment, the carrier collected by the image carrier squeezing rollers  13 Y,  13 M,  13 C, and  13 K can be reused, achieving effective use of the liquid developer. Further, since the color shift compensation mode is executed under the same condition as in the image forming mode provided in the image forming apparatus in terms of the removal amount of the carrier on the intermediate transfer member  40 , it is possible to prevent deterioration in the cleaning performance of the cleaning blade for cleaning the resist marks transferred onto the intermediate transfer medium  40 . That is, according to the present invention, there can be provided an image forming apparatus capable of achieving both the prevention of deterioration in the resist mark detection accuracy and prevention of deterioration in the cleaning performance with respect to the intermediate transfer member in a balanced manner. 
         [0140]    Next, a fourth embodiment of the present invention will be described.  FIGS. 6 and 7  are views showing main components constituting an image forming apparatus according to the fourth embodiment of the present invention, and  FIG. 8  is a cross-sectional view showing main components of an image forming section and developing unit in the fourth embodiment of the present invention. 
         [0141]    In the third embodiment, each squeezing unit corresponding to each of the image carriers  10 Y,  10 M,  10 C, and  10 K has one image carrier squeezing roller, while in the present embodiment, each squeezing unit has two image carrier squeezing rollers. That is, in the image forming apparatus according to the present embodiment, image carrier squeezing rollers  13 Y′,  13 M′,  13 C′, and  13 K′ are provided in addition to the image carrier squeezing rollers  13 Y,  13 M,  13 C, and  13 K. Further, in the present embodiment, the image carrier squeezing rollers  13 Y,  13 M,  13 C, and  13 K are arranged so as to freely abut and separate thereon from the image carriers  10 Y,  10 M,  10 C, and  10 K. 
         [0142]    Also in the fourth embodiment, at the execution time of the first type recording medium image forming mode, the removal amount of the carrier on the intermediate transfer member  40  is increased as compared to the removal amount in the second type recording medium image forming mode. To this end, in the fourth embodiment, when executing the first type recording medium image forming mode, the image carrier squeezing rollers  13 Y,  13 M,  13 C, and  13 K that have been separated from the image carriers  10 Y,  10 M,  10 C, and  10 K in a normal state are brought into abutting the image carriers  10 Y,  10 M,  10 C, and  10 K to remove a larger amount of carrier on the image carriers  10 Y,  10 M,  10 C, and  10 K than in the second type recording medium image forming mode and thus to increase the removal amount of the carrier on the intermediate transfer member  40 . The same carrier removal condition as in this first type recording medium forming mode may be applied to the color shift compensation mode. An example of conditions at the execution time of the first and second type recording medium image forming modes in the fourth embodiment is shown in the following Table 5. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 5 
               
             
             
               
                   
                   
               
               
                   
                   
                 Second type 
               
               
                   
                 First type 
                 recording medium 
               
             
          
           
               
                   
                 recording medium 
                 High- 
                   
               
             
          
           
               
                   
                 Art 
                 Coated 
                 quality 
                 Regular 
               
               
                   
                 paper 
                 paper 
                 paper 
                 paper 
               
               
                   
                   
               
             
          
           
               
                 Number of squeezing rollers 
                 2 
                 1 
               
               
                 abutting image carriers 
               
               
                 Peripheral speed 
                 200 
                 200 
               
               
                 of image carrier 
               
               
                 squeezing roller [mm/s] 
               
               
                 Solid content ratio 
                 40 
                 35 
               
               
                 on intermediate transfer member 
               
               
                 observed at position of optical 
               
               
                 sensor 90 [%] 
               
               
                   
               
             
          
         
       
     
         [0143]    Further, in the first type recording medium image forming mode, the image carrier squeezing rollers  13 Y,  13 M,  13 C, and  13 K brought into abutting the image carriers may be controlled to be rotated at a peripheral rotation speed higher than that of the image carriers  10 Y,  10 M,  10 C, and  10 K so as to increase the removal amount of the carrier on the image carriers  10 Y,  10 M,  10 C, and  10 K and thus to increase the removal amount of the carrier on the intermediate transfer member  40  as compared to the removal amount in the second type recording medium image forming mode. The same carrier removal condition as in this first type recording medium image forming mode may be applied to the color shift compensation mode. 
         [0144]    Further, in the first type recording medium image forming mode, the image carrier squeezing rollers  13 Y,  13 M,  13 C, and  13 K brought into abutting the image carriers may be controlled to be rotated in the reverse direction to the rotation direction of the image carriers  10 Y,  10 M,  10 C, and  10 K at the respective nip portions so as to increase the removal amount of the carrier on the image carriers  10 Y,  10 M,  10 C, and  10 K and thus to increase the removal amount of the carrier on the intermediate transfer member  40  as compared to the removal amount in the second type recording medium image forming mode. The same carrier removal condition as in this first type recording medium image forming mode may be applied to the color shift compensation mode. 
         [0145]    Further, in the first type recording medium image forming mode, the image carrier squeezing rollers  13 Y,  13 M,  13 C, and  13 K brought into abutting the image carriers may be controlled to be rotated at a peripheral rotation speed higher than the rotation speed of the image carriers  10 Y,  10 M,  10 C, and  10 K in the reverse direction to the rotation direction of the image carriers  10 Y,  10 M,  10 C, and  10 K at the respective nip portions. The same carrier removal condition as in such a first type recording medium image forming mode may be applied to the color shift compensation mode. 
         [0146]    As described above, according to the fourth embodiment of the present invention, since the color shift compensation mode is executed under the same condition as in the first type recording medium image forming mode in which the removal amount of the carrier on the intermediate transfer member  40  is increased as compared to the removal amount in the second type recording medium image forming mode, the position information of the resist marks can be accurately acquired without deterioration in the accuracy of the resist mark detection results obtained by the optical sensor, thereby achieving accurate color shift compensation. Further, in the present embodiment, the carrier collected by the image carrier squeezing rollers  13 Y,  13 M,  13 C, and  13 K can be reused, achieving effective use of the liquid developer. Further, since the color shift compensation mode is executed under the same condition as in the image forming mode provided in the image forming apparatus in terms of the removal amount of the carrier on the intermediate transfer member  40 , it is possible to prevent deterioration in the cleaning performance of the cleaning blade for cleaning the resist marks transferred onto the intermediate transfer medium  40 . 
         [0147]    As a reference, an example of parameters in image forming processes in the first and second type recording medium image forming modes are shown in the following Table 6. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 6 
               
             
             
               
                   
                   
               
               
                   
                 First type 
                   
               
               
                   
                 recording 
                 Second type 
               
               
                   
                 medium 
                 recording medium 
               
             
          
           
               
                   
                 Art 
                 Coated 
                 High-quality 
                 Regular 
               
               
                   
                 paper 
                 paper 
                 paper 
                 paper 
               
               
                   
                   
               
             
          
           
               
                 Exposure 
                 Light amount 
                 0.7 
                 0.8 
               
               
                 process 
                 [μJ/cm 2 ] 
               
               
                 Charging 
                 Bias voltage 
                 600 
                 700 
               
               
                 process 
                 [V] 
               
               
                 Developing 
                 Bias voltage 
                 450 
                 550 
               
               
                 process 
                 [V] 
               
               
                   
                 Peripheral 
                 247 
                 420 
               
               
                   
                 speed of 
               
               
                   
                 anilox roller 
               
               
                   
                 [mm/s] 
               
               
                   
                 Developer 
                 6.5 
                 10 
               
               
                   
                 film thickness 
               
               
                   
                 [μm] 
               
               
                   
               
             
          
         
       
     
         [0148]    There is a case where a mode (low-speed mode) in which the moving speed of the intermediate transfer member  40  and speed of various processes associated with the intermediate transfer member  40  are made lower than the speed of an ordinary printing speed in accordance with the paper type (especially, thickness of the paper) is provided. However, such a low-speed mode is not applied to the color shift compensation mode of the present invention. That is, in order to execute the color shift compensation mode, the moving speed of the intermediate transfer member  40  needs to be the same in each of a plurality of image forming modes provided in the image forming apparatus. This is because that the condition for the color shift compensation changes in accordance with the moving speed of the intermediate transfer member  40 . 
         [0149]    As a reference, an example of parameters in the low-speed mode image forming process is shown in the following Table 7. 
         [0000]    
       
         
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                 Low-speed mode 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Exposure process 
                 Light amount 
                 0.65 
               
               
                   
                   
                 [μJ/cm 2 ] 
               
               
                   
                 Charging process 
                 Bias voltage 
                 550 
               
               
                   
                   
                 [V] 
               
               
                   
                 Developing process 
                 Bias voltage 
                 400 
               
               
                   
                   
                 [V] 
               
               
                   
                   
                 Peripheral speed of 
                 247 
               
               
                   
                   
                 anilox roller 
               
               
                   
                   
                 [mm/s] 
               
               
                   
                   
                 Developer film 
                 6.5 
               
               
                   
                   
                 thickness 
               
               
                   
                   
                 [μm] 
               
               
                   
                   
               
             
          
         
       
     
         [0150]    Next, a fifth embodiment of the present invention will be described.  FIGS. 9 and 10  are views showing main components of a developing unit in the image forming apparatus according to the fifth embodiment of the present invention. The present embodiment can be practiced in parallel with the embodiments described above. 
         [0151]    In the color shift compensation mode of the present embodiment, the carrier contained in the resist marks is removed while the removal amount thereof is controlled so as not to be excessive. More specifically, as in the case of the above embodiments, the color shift compensation mode is executed under a condition of the same carrier removal amount as in the image forming mode in which the removal amount of the carrier on the intermediate transfer member  40  is largest of all the image forming modes provided in the image forming apparatus. 
         [0152]    In the present embodiment, as a plurality of image forming modes provided in the image forming apparatus, those in which toner consumption amount for use in an image forming process differs from one another can be adopted. More specifically, the image forming apparatus according to the fifth embodiment has a normal printing mode and a toner-saving printing mode in which an image forming process is carried out with a smaller toner amount than in the normal printing mode. 
         [0153]    In the toner-saving printing mode, the amount of a liquid developer supplied from the anilox roller  32  to the developing roller  20  is controlled to be reduced as compared to that in the normal printing mode. The carrier amount on the intermediate transfer member  40  is proportional to the supply of the liquid developer. Thus, in the present embodiment, the same carrier condition as in the toner-saving printing mode is applied to the color shift compensation mode. 
         [0154]    A method of controlling the amount of the liquid developer supplied from the anilox roller  32  to developing roller  20  will be described with reference to  FIGS. 9A and 9B  by taking the developing unit of yellow as an example. Since the developing units of respective colors have the same configuration, only the developing unit of yellow will be described below. 
         [0155]    In the example of  FIGS. 9A and 9B , in order to control the amount of the liquid developer supplied from the anilox roller  32 Y to developing roller  20 Y, the pressing force of the restricting blade  33 Y is changed. More specifically, assuming that the pressing force of the restricting blade  33 Y in the normal printing mode is F 1  and pressing force thereof in the toner-saving printing mode is F 2 , F 2  is set larger than F 1  to thereby reduce the amount of the liquid developer supplied from the anilox roller  32 Y to developing roller  20 Y at the execution time of the toner-saving printing mode. 
         [0156]    Another method of controlling the amount of the liquid developer supplied from the anilox roller  32  to developing roller  20  will be described with reference to  FIGS. 10A and 10B . 
         [0157]    In the example of  FIGS. 10A and 10B , in order to control the amount of the liquid developer supplied from the anilox roller  32 Y to developing roller  20 Y, the rotation speed of the anilox roller  32 Y is changed. More specifically, assuming that the peripheral speed of the anilox roller  32 Y in the normal printing mode is V 1  and peripheral speed thereof in the toner-saving printing mode is V 2 , V 1  is set larger than V 2  to thereby reduce the amount of the liquid developer supplied from the anilox roller  32 Y to developing roller  20 Y at the execution time of the toner-saving printing mode. 
         [0158]    The methods described using  FIGS. 9 and 10  can be used in a combined manner so as to control the amount of the liquid developer supplied from the anilox roller  32 Y to the developing roller  20 Y. 
         [0159]    In the manner as described above, the amount of the liquid developer supplied for the image forming process is reduced in the toner-saving printing mode as compared to that in the normal printing mode and, correspondingly, the carrier amount on the intermediate transfer member  40  is reduced. In the present embodiment, the same condition as in this toner-saving printing mode is applied to the color shift compensation mode. 
         [0160]    As described above, according to the fifth embodiment of the present invention, since the color shift compensation mode is executed under the same condition as in the toner-saving printing mode in which the carrier amount on the intermediate transfer member  40  is reduced as compared to the carrier amount in the normal printing mode, the position information of the resist marks can be acquired without deterioration in the accuracy of the resist mark detection results obtained by the optical sensor, thereby achieving accurate color shift compensation. Further, since the color shift compensation mode is executed under the same condition as in the image forming mode provided in the image forming apparatus in terms of the amount of the carrier on the intermediate transfer member  40 , it is possible to prevent deterioration in the cleaning performance of the cleaning blade for cleaning the resist marks transferred onto the intermediate transfer medium  40 . That is, according to the present invention, there can be provided an image forming apparatus capable of achieving both the prevention of deterioration in the resist mark detection accuracy and prevention of deterioration in the cleaning performance with respect to the intermediate transfer member in a balanced manner. 
         [0161]    As a reference, an example of parameters in the image forming process of the toner-saving printing mode is shown in the following Table 8. 
         [0000]    
       
         
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 8 
               
               
                   
                   
               
               
                   
                 Toner-saving mode 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Exposure process 
                 Light amount 
                 0.7 
               
               
                   
                   
                 [μJ/cm 2 ] 
               
               
                   
                 Charging process 
                 Bias voltage 
                 600 
               
               
                   
                   
                 [V] 
               
               
                   
                 Developing process 
                 Bias voltage 
                 450 
               
               
                   
                   
                 [V] 
               
               
                   
                   
                 Peripheral speed of 
                 213 
               
               
                   
                   
                 anilox roller 
               
               
                   
                   
                 [mm/s] 
               
               
                   
                   
                 Developer film 
                 5.8 
               
               
                   
                   
                 thickness 
               
               
                   
                   
                 [μm] 
               
               
                   
                   
               
             
          
         
       
     
         [0162]    The processing performed in the color shift compensation mode will be described in more detail below.  FIG. 12  is a view showing a flowchart of the color shift compensation mode processing. As shown in  FIG. 12 , after the start of the color shift compensation processing, calibration of the optical sensor  90  for detecting the resist marks are performed to adjust the light-emitting amount of the sensor such that the surface output of the intermediate transfer member  40  assumes a predetermined voltage. Then, the condition of the carrier removal amount is set to the first condition which is the same condition as in the first type recording medium image forming mode. 
         [0163]    Subsequently, the resist marks are formed on the intermediate transfer member  40 , and the formed resist marks are detected using the optical sensor  90 . Main-scanning direction resist displacement amounts, sub-scanning direction resist displacement amounts, and skew amounts are calculated from the detection results of the resist marks and then, based on the calculated values, resist compensation amounts (the main-scanning direction resist compensation values, sub-scanning direction resist compensation values, and skew compensation values) are set for respective colors. 
         [0164]    Resist marks for sub-scanning direction resist displacement (skew amount) detection and resist marks for main-scanning direction resist displacement detection are shown in  FIGS. 13 and 14 , respectively. 
       (Resist Displacement Amount Calculation Method) 
       [0165]    Calculation methods of the main-scanning direction resist displacement amount, sub-scanning direction resist displacement amount, and skew amount will be described. The resist displacement amount and skew amount for each color can be calculated from detection result (edge time information) of a predetermined resist mark. The following description is made for a case where K (black) is set as a reference color. 
         [0166]    Main-Scanning Direction Displacement Amount Calculation Method 
         [0167]    The main-scanning direction resist displacement amount can be calculated from a detection result of a mark obtained by combining a straight line and diagonal line. The following Table 9 explains an example of parameters when black (K) is set as a reference.  FIG. 15  is a view showing a sensor output observed when resist marks are detected by means of the optical sensor  90 . 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 9 
               
               
                   
                   
               
               
                   
                 Time pitch between 
                   
               
               
                   
                 straight line and 
                 K-based resist 
               
               
                   
                 diagonal line 
                 displacement 
               
               
                   
                 (measurement value) 
                 amount 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Black (K) 
                 Lk 
                 — 
               
               
                   
                 Cyan (C) 
                 Lc 
                 Dc 
               
               
                   
                 Magenta (M) 
                 Lm 
                 Dm 
               
               
                   
                 Yellow (Y) 
                 Ly 
                 Dy 
               
               
                   
                   
               
             
          
         
       
     
         [0168]    First, the time pitches between the straight lines and diagonal lines of respective colors are calculated from the detection results of the resist marks, i.e., time information concerning the edges of the resist marks in the following manner. 
         [0000]        Lk ={( t 3− t 1)+( t 4− t 2)}/2 
         [0000]        Lc ={( t 7− t 5)+( t 8 −t 6)}/2 
         [0000]        Lm ={( t 11− t 9)+( t 12− t 10)}/2 
         [0000]        Ly ={( t 15 −t 13)+( t 16− t 14)}/2 
         [0169]    Then, the main-scanning direction resist displacement amounts of respective colors with respect to the reference color (in this case, K) are calculated from the time pitches of the respective colors in the following manner. 
         [0000]    
       
      
       Dc=Lc−Lk  
      
     
         [0000]    
       
      
       Dm=Lm−Lk  
      
     
         [0000]    
       
      
       Dy=Ly−Lk  
      
     
         [0170]    Resist compensation values are set based on the resist displacement amounts and, based on the compensation values, the main-scanning direction light-emitting positions of the exposure units such as a line head (LED, OPH) other than the reference color are changed to compensate the main-scanning direction resist displacement. 
         [0171]    Sub-Scanning Direction Displacement Amount Calculation Method 
         [0172]    The sub-scanning direction resist displacement amount can be calculated from a detection result of a straight line mark. The following Table 10 explains an example of parameters when black (K) is set as a reference.  FIG. 16  is a view showing a sensor output observed when resist marks are detected by means of the optical sensor  90 . 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 10 
               
               
                   
                   
               
               
                   
                   
                 K-based 
                 K-based 
               
               
                   
                 K-based 
                 time pitch 
                 resist 
               
               
                   
                 time pitch 
                 (measurement 
                 displacement 
               
               
                   
                 (design vale) 
                 value) 
                 amount 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Cyan (C) 
                 pc 
                 Pc 
                 Rc 
               
               
                   
                 Magenta (M) 
                 pm 
                 Pm 
                 Rm 
               
               
                   
                 Yellow (Y) 
                 py 
                 Py 
                 Ry 
               
               
                   
                   
               
             
          
         
       
     
         [0173]    First, the time pitches between the resist marks of the respective colors and that of the reference color are calculated from the detection results of the resist marks, i.e., time information concerning the edges of the resist marks in the following manner. 
         [0000]        Pc =(( t 3− t 1)+( t 4− t 2))/2 
         [0000]        Pm =(( t 5− t 1)+( t 6− t 2))/2 
         [0000]        Py =(( t 7− t 1)+( t 8− t 2))/2 
         [0174]    Then, the sub-scanning direction resist displacement amounts of respective colors are calculated from the time pitches of the respective colors and design values in the following manner. 
         [0000]    
       
      
       Rc=Pc−pc  
      
     
         [0000]    
       
      
       Rm=Pm−pm  
      
     
         [0000]    
       
      
       Ry=Py−py  
      
     
         [0175]    Resist compensation values are set based on the resist displacement amounts and, based on the compensation values, the sub-scanning direction light-emitting timings of the exposure units such as a line head (LED, OPH) other than the reference color are changed to compensate the sub-scanning direction resist displacement. 
         [0176]    Skew Amount 
         [0177]    The skew amount of each color can be calculated from a detection result of sub-scanning direction resist marks formed on both ends of the intermediate transfer belt  41 . The following table 11 explains an example of parameters when black (K) is set as a reference.  FIG. 17  is a view schematically showing a state where resist marks are detected by means of an optical sensor  90 . In this case, two sensor outputs from a front side sensor and rear side sensor provided on one side of the roller and the like in the shaft direction thereof are used. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 11 
               
               
                   
                   
               
               
                   
                 K-based 
                 K-based 
                   
               
               
                   
                 time pitch 
                 time pitch 
               
               
                   
                 (front side 
                 (rear side 
               
               
                   
                 measurement 
                 measurement 
                 K-based 
               
               
                   
                 value) 
                 value) 
                 skew amount 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Cyan (C) 
                 Pcf 
                 Pcr 
                 Sc 
               
               
                   
                 Magenta (M) 
                 Pcm 
                 Pmr 
                 Sm 
               
               
                   
                 Yellow (Y) 
                 Pcy 
                 Pyr 
                 Sy 
               
               
                   
                   
               
             
          
         
       
     
         [0178]    The time pitches between the resist marks of the respective colors and that of the reference color are calculated from the time information concerning the edges of the resist marks which are obtained at both ends (front side and rear side) of the intermediate transfer member  40  in the direction perpendicular to the moving direction thereof, and the skew amounts are calculated based on a difference between the time pitches at the both ends of the intermediate transfer belt  41  in the following manner. 
         [0000]    
       
      
       Sc=Pcf−Pcr  
      
     
         [0000]    
       
      
       Sm=Pmf−Pmr  
      
     
         [0000]    
       
      
       Sy=Pyf−Pyr  
      
     
         [0179]    Skew compensation values are set based on the skew amounts and, based on the compensation values, the sub-scanning direction light-emitting timings of the exposure units such as a line head (LED, OPH) other than the reference color are changed for each chip or for each dot to compensate the skew. 
         [0180]    Although the present invention has been described with reference to the various embodiments, an embodiment obtained by arbitrarily combining a part or all of the configurations of the above embodiments is included in the scope of the present invention.