Abstract:
An image forming system which is capable of causing a clear coating apparatus to discharge processed sheets in proper page order, and improving usability and operability of the system by users. An mage forming apparatus is set to perform single-sided image formation or double-sided image formation. A clear coating apparatus is set to perform single-sided clearing coating or double-sided clear coating. Whether to perform inverted discharge of sheets is controlled according to the settings of the image forming apparatus and the clear coating apparatus.

Description:
[0001]    This is a continuation of patent application Ser. No. 11/758,423 filed Jun. 5, 2007, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an image forming system comprised of an image forming apparatus that forms an image on a sheet, and a clear coating apparatus connected to the image forming apparatus on a downstream side of the same so as to perform clear coating on the sheet using clear toner which becomes clear (transparent) after being fixed on the sheet. 
         [0004]    2. Description of the Related Art 
         [0005]    In recent years, there has been an increasing demand for full-color electrophotographic image forming apparatuses ensuring high image quality. Further, it has been increasingly desired to realize a high-quality photographic tone image mode in an electrophotographic image forming apparatus, with proliferation of digital cameras as a major reason. 
         [0006]    Further, there has been proposed an image forming system that is comprised of an image forming apparatus and a clear coating apparatus continuously connected thereto, and is configured to form a high-quality photographic tone image on a sheet, and then place thereon a toner image which becomes transparent when fixed, to thereby perform clear coating on the formed image (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. H03-13079). 
         [0007]    Further, there has been a system including apparatuses continuously connected to each other, in which an upstream one of the continuously connected apparatuses performs printing on a first surface of a sheet, and a downstream one of the apparatuses performs printing on a second surface of the sheet, to thereby realize double-sided printing without the provision of a sheet-inverting mechanism (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. 2003-207954). 
         [0008]    The above system with the continuously connected apparatuses is aimed at improving productivity, and hence double-sided printing is not performed within any of the apparatuses. Therefore, when the upstream one of the apparatuses performs double-sided printing on each sheet and discharges the sheet, according to a conventional job sequence, if the downstream one of the apparatuses also perform double-sided printing on the sheet, this causes the problem of an improper page order of the discharged printed sheets. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides an image forming system which is capable of causing a clear coating apparatus to discharge processed sheets in proper page order, and improving usability and operability of the system by users. 
         [0010]    In a first aspect of the present invention, there is provided an image forming system including an image forming apparatus that performs image formation on sheets, and a clear coating apparatus that performs clear coating using a clear toner, comprising an inverted discharge section adapted to discharge each sheet after inverting the sheet upside down, a setting unit adapted to set the image forming apparatus such that the image forming apparatus performs single-sided image formation or double-sided image formation, and set the clear coating apparatus such that clear coating apparatus performs single-sided clearing coating or double-sided clear coating, and a controller adapted to control the inverted discharge section according to settings of the image forming apparatus and the clear coating apparatus by the setting unit. 
         [0011]    The image forming system according to the first aspect of the present invention comprises the controller that controls the inverted discharge section according to a combination of an image forming mode (single-sided image formation or double-sided image formation) of the image forming apparatus and a clear coat image-forming mode (single-sided clear coating or double-sided clear coating) of the clear coating apparatus. Therefore, it is possible to cause the clear coating apparatus to discharge the sheets in proper page order, and improve usability and operability of the system by users. 
         [0012]    When performing image formation on a plurality of sheets and discharge the sheets out of the clear coating apparatus in a predetermined order, the controller can control the inverted discharge section to invert each sheet upside down, when the setting unit configures the settings to cause the image forming apparatus to perform double-sided image formation and cause the clear coating apparatus to perform double-sided clear coating. 
         [0013]    The controller can control the inverted discharge section not to invert each sheet upside down, when the setting unit configures the settings to cause the image forming apparatus to perform double-sided image formation and cause the clear coating apparatus not to perform clear coating. 
         [0014]    The controller can control the inverted discharge section not to invert each sheet upside down, when the setting unit configures the settings to cause the image forming apparatus to perform single-sided image formation and cause the clear coating apparatus to perform double-sided clear coating. 
         [0015]    When performing image formation on a plurality of sheets and discharge the sheets out of the clear coating apparatus in a predetermined order, the controller can control the inverted discharge section to invert each sheet upside down, when the setting unit configures the settings to cause the image forming apparatus to perform single-sided image formation and cause the clear coating apparatus to perform single-sided clear coating. 
         [0016]    When performing image formation on a plurality of sheets and discharge the sheets out of the clear coating apparatus in a predetermined order, the controller controls the inverted discharge section to invert each sheet upside down, when the setting unit configures the settings to cause the image forming apparatus to perform single-sided image formation and cause the clear coating apparatus not to perform clear coating. 
         [0017]    In a second aspect of the present invention, there is provided an image forming system including an image forming apparatus that performs image formation on sheets, and a clear coating apparatus that performs clear coating using a clear toner, comprising an inverted discharge section adapted to discharge each sheet after inverting the sheet upside down, a setting unit adapted to set the image forming apparatus such that the image forming apparatus performs single-sided image formation or double-sided image formation, and set the clear coating apparatus such that clear coating apparatus performs single-sided clearing coating or double-sided clear coating, and an image formation order-changing section adapted to change an order of pages of each sheet to be subjected to image formation by the image forming apparatus. 
         [0018]    The image forming system according to the second aspect of the present invention includes an image forming order-changing section that changes an order of pages according to a combination of the image forming mode (single-sided image formation or double-sided image formation) of the image forming apparatus and the clear coat image-forming mode (single-sided clear coating or double-sided clear coating) of the clear coating apparatus. Therefore, it is possible to cause the clear coating apparatus to discharge the sheets in proper page order, and improve usability and operability of the system by users. 
         [0019]    When performing image formation on a plurality of sheets and discharge the sheets out of the clear coating apparatus in a predetermined order, the image formation order-changing section reverses the order of pages of each sheet to be subjected to double-sided image formation by the image forming apparatus, when the setting unit configures the settings to cause the image forming apparatus to perform double-sided image formation and cause the clear coating apparatus to perform double-sided clear coating. 
         [0020]    The image formation order-changing section can set the order of pages of each sheet to be subjected to double-sided image formation by the image forming apparatus, to a normal page order, when the setting unit configures the settings to cause the image forming apparatus to perform double-sided image formation and cause the clear coating apparatus not to perform clear coating. 
         [0021]    The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a schematic view of an image forming system according to a first embodiment of the present invention. 
           [0023]      FIG. 2  is a view of an operation panel of an image forming apparatus appearing in  FIG. 1 . 
           [0024]      FIG. 3  is a schematic diagram of the circuit configuration of the image forming apparatus. 
           [0025]      FIG. 4  is a schematic diagram of the circuit configuration of a clear coating apparatus appearing in  FIG. 1 . 
           [0026]      FIG. 5  is a flowchart of a clear coating process executed by the image forming system in  FIG. 1 . 
           [0027]      FIG. 6  is a flowchart showing a procedure of outside-discharge processing executed in a step S 106  in  FIG. 5 . 
           [0028]      FIG. 7  is a diagram of a table showing the relationship between an image formation mode of the image forming apparatus, a clear coating mode of the clear coating apparatus, and an inverted discharge operation set to the clear coating apparatus. 
           [0029]      FIG. 8  is a diagram showing changes in the normal/reversed position of each sheet, which occur according to the present embodiment as the sheet is passed from the image forming apparatus after being subjected to double-sided image formation, subjected to double-sided clear coating, and then discharged out of the system after being subjected to inverted discharge processing. 
           [0030]      FIG. 9  is a diagram showing changes in the normal/reversed position of each sheet, which occur according to a variation of the present embodiment as the sheet is passed from the image forming apparatus after being subjected to double-sided image formation, subjected to double-sided clear coating, and then discharged out of the system. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    The present invention will now be described in detail below with reference to the drawings showing preferred embodiments thereof. 
         [0032]      FIG. 1  is a schematic view of an image forming system according to the first embodiment of the present invention. 
         [0033]    As shown in  FIG. 1 , the image forming system according to the present embodiment is comprised of an image forming apparatus  100 , and a clear coating apparatus  200  connected to the image forming apparatus  100  on a downstream side of the same. In the present embodiment, the image forming apparatus  100  is described as a color image forming apparatus, but it may be a monochrome one. 
         [0034]    The image forming apparatus  100  includes a platen glass  101  as an original platen, and a scanner  102 . The scanner  102  is comprised of an original illuminating lamp  103 , scanning mirrors  104  to  106 , a lens  107 , and an image sensor unit  108 . 
         [0035]    The scanner  102  is driven by a motor, not shown, to reciprocate for scanning in a predetermined direction. During this motion of the scanner  102 , a reflected light from an original passes through the lens  107  via the scanning mirrors  104  to  106  to form an image on a CCD sensor provided in the image sensor unit  108 . 
         [0036]    The exposure controller  109  is comprised of a laser, a polygon scanner, and so forth. The exposure controller  109  causes a laser beam  119  modulated based on an image signal converted into an electric signal by the image sensor unit  108  and having undergone predetermined image processing, referred to hereinafter, to reflect on a reflecting mirror  110  to thereby irradiate a photosensitive drum  111  with the laser beam  119 . The exposure controller  109  of the image forming apparatus  100  will be described in more detail hereinafter with reference to  FIG. 3 . 
         [0037]    Around the photosensitive drum  111 , there are arranged a pre-exposure lamp  121  for erasing potential on the photosensitive drum  111 , and a primary electrostatic charger  112  for applying potential to the photosensitive drum  111 . The primary electrostatic charger  112  applies a high voltage to a wire to thereby generate corona discharge. 
         [0038]    Further, around the photosensitive drum  111 , there are arranged a developing rotary  117 , an intermediate transfer member  118  for temporarily holding thereon an image developed on the photosensitive drum  111 , a primary transfer roller  122  for transferring the image onto the intermediate transfer member  118 , and a photosensitive drum cleaner  120 . 
         [0039]    Developing devices  113  to  116  filled with toners for developing an electrostatic latent image formed by irradiating the photosensitive drum  111  with the laser beam  119  are housed in the developing rotary  117  that sequentially brings the developing devices  113  to  116  into contact with the photosensitive drum  111 . 
         [0040]    The photosensitive drum  111  is rotated by a motor, not shown, and is charged to a desired potential by the primary electrostatic charger  112 . Then, the laser beam  119  emitted from the exposure controller  109  is reflected on the reflecting mirror  110  to be irradiated onto the photosensitive drum  111 . This causes an electrostatic latent image to be formed on the photosensitive drum  111 . 
         [0041]    The developing rotary  117  rotates to bring the developing device  113  for a first color into contact with the photosensitive drum  111  and electrostatically applies a toner from the developing device  113  onto the electrostatic latent image on the photosensitive drum  111  to thereby form a toner image on the photosensitive drum  111 . 
         [0042]    In the case of forming a full-color image with toners of four colors contained in the respective developing devices  113  to  116 , the first-color toner image developed on the photosensitive drum  111  is primarily transferred onto the intermediate transfer member  118  by the primary transfer roller  122 . Then, the developing rotary  117  rotates to bring the developing device  114  for a second color into contact with the photosensitive drum  111 . 
         [0043]    At this time, the laser beam  119  is emitted again from the exposure controller  109  in timing in which the leading end of the first-color toner image primarily transferred onto the intermediate transfer member  118  and that of a second-color toner image to be developed on the photosensitive drum  111  are perfectly aligned with each other at a position corresponding to the primary transfer roller  122 . 
         [0044]    Similarly to the first-color toner image, the second-color toner image is formed on the photosensitive drum  111  by the developing device  114  for the second color being brought into contact with the drum  111 . The toner image is superimposed by the primary transfer roller  122  on the first-color toner image primarily transferred onto the intermediate transfer member  118 . This superimposing operation is repeatedly carried out for a third color and a fourth color, whereby the full-color developed image of the four colors is eventually transferred onto the intermediate transfer member  118 . 
         [0045]    A sheet is fed from one of a first sheet feed cassette  133 , a second sheet feed cassette  134 , a third sheet feed cassette  135 , and a fourth sheet feed cassette  136  by an associated one of pickup rollers  125  to  128 . The sheet fed from the sheet feed cassette is conveyed toward a registration roller  143  by an associated one of feed rollers  129  to  132 . 
         [0046]    The sheet is conveyed to the vicinity of the registration roller  143  at rest, and then conveyed to a secondary transfer roller  123  by the registration roller  143  when the registration roller  143  is driven such that the leading end of the sheet is aligned with that of the developed image transferred onto the intermediate transfer member  118 . Then, a transfer bias is applied to the secondary transfer roller  123 , whereby the image is secondarily transferred onto the sheet. Thereafter, the sheet is conveyed to a conveyor belt  144 . 
         [0047]    On the intermediate transfer member  118 , there remains residual toner which was not transferred onto the sheet by the secondary transfer roller  123 . The residual toner is cleaned by an intermediate transfer member cleaner  124 . The intermediate transfer member cleaner  124  is disposed in a manner contactable with the intermediate transfer member  118 , and comes into contact with the intermediate transfer member  118  immediately before the leading end of the residual toner of the secondarily transferred image reaches the intermediate transfer member cleaner  124 . 
         [0048]    Then, the intermediate transfer member cleaner  124  is controlled to move apart from the intermediate transfer member  118  immediately before the leading end of a first-color developed image of a next toner image, which was transferred onto the intermediate transfer member  118  by the primary transfer roller  122 , reaches the intermediate transfer member cleaner  124 . 
         [0049]    There also remains residual toner on the photosensitive drum  111  after the toner image thereon has been transferred onto the intermediate transfer member  118 . This residual toner is cleaned by a photosensitive drum cleaner  120 . Thereafter, residual charge on the photosensitive drum  111  is erased by the pre-exposure lamp  121 . 
         [0050]    The sheet with the image secondarily transferred from the intermediate transfer member  118  is conveyed to a fixing device  145  by the conveyor belt  144 . The fixing device  145  is comprised of an upper heat roller, and a fixing belt for being pressed against the heat roller from below. The toner image secondarily transferred onto the sheet is fixed on the sheet by being pressed and heated by the fixing device  145 . Then, the sheet is discharged from the image forming apparatus  100  by an inner discharge roller  147  and an outer discharge roller  148 . 
         [0051]    In  FIG. 1 , a discharge flapper  146  switches the course of a sheet between a conveying path  138  and an inverting path  139 . In the case of double-sided recording (double-sided image formation) for forming images on the respective opposite sides of a sheet, a sheet conveyed by the inner discharge roller  147  is advanced into the inverting path  139  by shifting the discharge flapper  146  upward, and conveyed into an inversion conveying path  140 . 
         [0052]    Thereafter, the advancing direction of the sheet is reversed by switching a flapper  137 , whereby the sheet is guided into a refeed path  141  in an inverted state. On a fore end of the refeed path  141 , there is disposed a refeed roller  142  for refeeding the sheet to an image forming position (transfer position). 
         [0053]    The outer discharge roller  148  is disposed in the vicinity of the discharge flapper  146 , and a sheet whose course is switched to the conveying path  138  by the discharge flapper  146  is discharged from the image forming apparatus  100  by the outer discharge roller  148 . In the case of discharging a sheet from the image forming apparatus  100  after inverting the same, the discharge flapper  146  is shifted upward, and the sheet is conveyed into the inverting path  139  by an inverting roller  149  until the trailing end of the sheet passes by an inverting flapper  150 . Then, the inverting flapper  150  is switched, and the inverting roller  149  is reversely rotated, whereby the sheet is conveyed toward the outer discharge roller  148  after being inverted. 
         [0054]    An automatic document feeder (ADF)  170  automatically feeds an original to a position where the original can be read by the scanner  102 . 
         [0055]    The ADF  170  is comprised of an original tray  171  on which a maximum of one hundred originals can be placed, an original feed roller  172  for feeding originals, an original side inverting roller  173  for enabling double-sided reading of an original fed by the original feed roller  172 , and an original conveying belt  174 . 
         [0056]    The original conveying belt  174  conveys an original conveyed by the original feed roller  172  or the original side inverting roller  173 , onto the platen glass  101 . The original conveying belt  174  is controlled to stop the original in a reading position, and then discharge the original onto an original discharge tray  175 , provided that in the case of reading the reverse side of the original, it is controlled to return the original to the original side inverting roller  173  before discharging the same onto the original discharge tray  175 . The original discharge tray  175  can also have a maximum of one hundred originals loaded thereon. 
         [0057]    Units of the clear coating apparatus  200 , which are designated by respective numerals  209  to  250  correspond to the units of the image forming apparatus  100 , which are designated by respective numerals  109  to  150 , and therefore duplicate description thereof is omitted. 
         [0058]    An exposure controller  209  of the clear coating apparatus  200  will be described in detail hereinafter with reference to  FIG. 4 . A developing device  213  contains a clear-colored toner. The clear toner originally has a whitish color, and becomes clear or transparent when heated by a fixing device. 
         [0059]    A sheet with an image formed by the image forming apparatus  100  is conveyed into the clear coating apparatus  200  by the outer discharge roller  148 . The sheet is received by a roller in the clear coating apparatus  200  and conveyed toward a registration roller  243 . An image forming operation and sheet conveying and discharging operations carried out thereafter are the same as those performed by the image forming apparatus  100 . 
         [0060]      FIG. 2  is a view of an operation panel of the image forming apparatus  100  in  FIG. 1 . 
         [0061]    As shown in  FIG. 2 , the operation panel  300  is comprised of an LCD display section  301 , a ten-key numeric keypad  302 , a start key  303 , a stop key  304 , a soft power key  305 , a power-saving mode key  306 , a reset key  307 , a guide key  308 , and a user mode key  309 . 
         [0062]    The touch panel-type LCD display section  301  is used to perform mode setting and status display. The ten-key numeric keypad  302  is comprised of input keys for inputting numerals 0 to 9 and a clear key for returning a set value to a default value. The start key  303  is pressed by the user so as to execute a copying function or a scanning function. 
         [0063]    The stop key  304  is pressed by the user so as to stop a job which is being carried out using the copying function, the printing function, or the scanning function. The soft power key  305  is pressed by the user so as to turn off the powers of respective loads, such as motors, of the image forming apparatus  100 , and keep a CPU and networking active. 
         [0064]    The power-saving mode key  306  is pressed by the user so as to perform temperature adjustment control of the fixing device  145  at a level set in a user mode. The reset key  307  is pressed so as to reset a function set via the LCD display section  301  or the ten-key numeric keypad  302  to a default value. 
         [0065]    The guide key  308  is pressed by the user so as to display an explanation of each of the copying function, the printing function, the scanning function, and user modes to be set/executed. 
         [0066]    The user mode key  309  is pressed by the user so as to set an adjustment mode for executing an adjustment item, such as gradation correction, which the user is allowed to execute as desired, as well as to carry out various kinds of network configurations, including IP address setting. 
         [0067]    The user can designate an operation mode, such as a single-sided clear coating mode or a double-sided clear coating mode, by operating the operation panel  300 . 
         [0068]      FIG. 3  is a schematic diagram of the circuit configuration of the image forming apparatus  100  in  FIG. 1 . 
         [0069]    Referring to  FIG. 3 , an operating section  400  is a circuit for controlling the operation panel  300  shown in  FIG. 2 . A job controller  401  is a circuit including a ROM in which are written programs for controlling the image forming apparatus  100 , a RAM in which the programs are loaded, and a CPU that executes the programs. 
         [0070]    The operating section  400  is connected to the job controller  401 , and the job controller  401  is notified of an operation mode designated via the operating section  400 . The job controller  401  generates a copy job, a scan job, or the like according to received operation mode information, based on a program stored in the job controller  401 . 
         [0071]    The job controller  401  is also connected to a reader control communication I/F  406  as a communication I/F with a CPU circuit, not shown, for controlling the scanner  102  for reading original images, and a clear coating apparatus control communication I/F  419  as a communication I/F with the clear coating apparatus  200 . 
         [0072]    Further, the job controller  401  is connected to a PDL control communication I/F  407  as a communication I/F with a CPU circuit of a PDL image controller, not shown, for expanding PDL image data received e.g. from a PC (personal computer), not shown, into a bitmap image. 
         [0073]    Furthermore, the job controller  401  is connected to an image controller  402  that controls image data based on which a PDL image and a reader image are delivered to each of developing stations of the image forming apparatus  100 , and a print controller  411  that drivingly controls the loads to form images. In short, the job controller  401  controls the overall operation of the image forming apparatus  100 . 
         [0074]    The image controller  402  is a circuit that configures image-related circuits according to a job generated by the job controller  401 . In the present embodiment, the image controller  402  receives 
         [0075]    PDL image data via a PDL image I/F  408 , and reader image data from a reader image I/F  409 . 
         [0076]    The image controller  402  sets an image selector  410  that determines which of the PDL image data and the reader image data is to be validated, and determines which area in an image memory  403  implemented by a volatile memory is to be used for storing the image data selected by the image selector  410 , as data to be validated. 
         [0077]    Further, the image controller  402  configures an image storage section  405  formed by a nonvolatile memory, typically an HDD, and performs configuration of an image compression/expansion section  404  for causing the same to compress bitmap image data received from the image memory  403  and send the compressed bitmap image data into the image storage section  405 . The image controller  402  also performs configuration of the image compression/expansion section  404  for causing the same to expand compressed image data received from the image storage section  405  and send the expanded image data to the image memory  403 . 
         [0078]    Further, the image controller  402  reads out color image data from the image memory  403  so as to actually develop and print the image data, and causes an image processing section  414  to perform desired image processing. The image processing section  414  receives and performs image processing on image data of each color delivered from the image memory  403  based on settings of the image controller  402  configured according to instructions from the job controller  401 . 
         [0079]    Further, the image controller  402  configures LUTs (Look-Up Tables)  415  such that the sensitivity characteristics of the photosensitive drum  111  is reflected on the image data. 
         [0080]    More specifically, when an image cannot have a desired density due to change of the sensitivity characteristics of the photosensitive drum  111  or a change in the amount of laser exposure or the amount of electric charge from the primary electrostatic charger  112 , each of the LUTs  415  changes the image density of input each color image data, whereby the image is converted into an image having the desired density. Each color image data having passed through an associated one of the LUTs  415  is output to an associated one of the lasers  416 , and an electrostatic latent image is formed on the photosensitive drum  111  by an associated one of the developing devices  113  to  116 . 
         [0081]    Further, the print controller  411  controls a sheet conveyance controller  412  in a manner synchronous with control of a print image controller  413 , such that a full-color toner image formed on the intermediate transfer member  118  is transferred onto a sheet fed from one of the sheet feed cassettes  133  to  136 . Furthermore, the print controller  411  provides control such that the transferred image is fixed on the sheet through the fixing device  145 . First and second patch sensors  417  and  418  are connected to the print image controller  413 . 
         [0082]      FIG. 4  is a schematic diagram of the circuit configuration of the clear coating apparatus  200  in  FIG. 1 . 
         [0083]    As shown in  FIG. 4 , a job controller  501  is a circuit including a ROM in which are written programs for controlling the clear coating apparatus  200 , a RAM in which the programs are loaded, and a CPU that executes the programs. 
         [0084]    A main apparatus control communication I/F  506  is connected to the job controller  501 , and instructions issued from the main apparatus (image forming apparatus  100 ) are sent to the job controller  501  via the main apparatus control communication I/F  506 . 
         [0085]    A single-sided clear coating operation, a double-sided clear coating operation, and so forth are carried out according to operation mode information in the received instructions, based on a program stored in the job controller  501 . The job controller  501  is connected to an image controller  502  and a print controller  511  that forms images by drivingly controlling loads. 
         [0086]    The image controller  502  expands image data sent from the main apparatus via a main apparatus image I/F  509  into a bitmap image. The image controller  502  also configures image-related circuits according to a job generated by the job controller  501 . In the present embodiment, image data sent to the image controller  502  via the main apparatus image I/F  509  is stored in an image memory  503 . 
         [0087]    Further, the image controller  502  configures an image storage section  505  formed by a nonvolatile memory, typically an HDD, and performs configuration of an image compression/expansion section  504  for causing the same to compress bitmap image data received from the image memory  503  and send the compressed bitmap image data into the image storage section  505 . The image controller  502  also performs configuration of the image compression/expansion section  504  for causing the same to expand compressed image data received from the image storage section  505  and send the expanded image data to the image memory  503 . Furthermore, the image controller  502  reads out clear coating image data from the image memory  503  so as to actually develop and print the image data, and causes an image processing section  514  to perform desired image processing. 
         [0088]    The image processing section  514  receives image data of each color delivered from the image memory  503  based on settings of the image controller  502  configured according to instructions from the job controller  501 , and performs image processing thereon to deliver the processed image data to LUTs  515 . 
         [0089]    Further, the image processing section  502  configures the LUTs  515  such that the sensitivity characteristics of a photosensitive drum  211  is reflected on the image data. When an image cannot have a desired density due to change of the sensitivity characteristics of the photosensitive drum  211  or a change in the amount of laser exposure or the amount of electric charge from a primary electrostatic charger  212 , each of the LUTs  515  changes the image density of input each color image data, whereby the image is converted into an image having the desired density. 
         [0090]    Each color image data having passed through an associated one of the LUTs  515  is output to an associated one of lasers  516 , and an electrostatic latent image is formed on the photosensitive drum  211  by the developing device  213 . 
         [0091]    Further, the print controller  511  controls a sheet conveyance controller  512  in a manner synchronous with control of the print image controller  513 , such that a clear toner image formed on an intermediate transfer member  218  is transferred onto a sheet conveyed from the image forming apparatus  100 . Furthermore, the print controller  511  provides control such that the transferred image is fixed on the sheet through a fixing device  245 . 
         [0092]      FIG. 5  is a flowchart of a clear coating process executed by the image forming system shown in  FIG. 1 . 
         [0093]    The present process is executed by the job controller  401  in  FIG. 3  and the job controller  501  in  FIG. 4 . 
         [0094]    Referring to  FIG. 5 , it is checked in a step  5101  whether or not a request for an operation has been received from the main apparatus (image forming apparatus  100 ). This step is repeatedly carried out before an operation is started. 
         [0095]    When a request for an operational arrives, the process proceeds to a step S 102 , wherein it is determined, based on instruction data sent from the image forming apparatus, whether or not clear coating is to be performed. If clear coating is to be performed, the process proceeds to a step S 107 , whereas if not, the process proceeds to a step S 103 . In the step S 103 , sheet passing processing is carried out so as to discharge a sheet from the apparatus without carrying out clear coating, and then the process proceeds to a step S 104 . In the step S 104 , processing for skipping clear coating is executed, and then the process immediately proceeds to a step S 105 . 
         [0096]    In the step S 105 , the sheet is conveyed without undergoing any processing, and if an instruction for inverted discharge has been received, the sheet is inverted, followed by the process proceeding to a step S 106 . In the step S 106 , outside-discharge processing is executed. Although a detailed description is omitted, if a device for passing a sheet out of the apparatus is provided, the processing by the device is executed, whereas if not, control is performed in consideration of stacking performance, followed by terminating the process. 
         [0097]    In the step S 107 , image passing from the image forming apparatus  100  is executed (if there is no image, this step is skipped). When there is no image, a whole surface of a sheet can be covered by a clear coating image, for example). Next, in a step S 108 , clear coating is performed on the sheet in the same manner as image formation is performed in a normal image forming process. 
         [0098]    In a step S 109 , it is determined whether or not double-sided clear coating is to be performed. 
         [0099]    If double-sided clear coating is to be performed, the process proceeds to a step S 110 , whereas if not, the process immediately proceeds to the outside-discharge processing (step S 106 ). 
         [0100]    In the step S 110 , the sheet is conveyed to a double-sided conveying section, and clear coating image data for the reverse side of the sheet is acquired. The processing, including double-sided conveyance, in this step is similar to that carried out by the image forming apparatus  100 , and hence detailed description thereof is omitted. Then, the process proceeds to a step S 111 , wherein it is determined whether or not clear coating image data for the reverse side of the sheet has been passed (received). If the image data has been received, the process proceeds to a step S 112 . In the step S 112 , the same processing as executed in the step S 108  is carried out. Then, the process proceeds to the step S 106 , followed by terminating the present process. 
         [0101]      FIG. 6  is a flowchart showing a procedure of outside-discharge processing executed in the step S 106  in  FIG. 5 . 
         [0102]    In  FIG. 6 , in a step S 201 , it is determined whether or not the sheet received from the image forming apparatus  100  has been subjected to double-sided image formation or single-sided image formation. If the sheet has been subjected to double-side image formation, the process proceeds to a step S 202 , whereas if the sheet is single-side image formation, the process proceeds to a step S 205 . 
         [0103]    In the step S 202 , it is determined whether or not the sheet has been subjected to double-sided clear coating. If the sheet has been subjected to double-sided clear coating, the sheet received from the image forming apparatus  100  is inverted upside down, compared with the state of the sheet received from the image forming apparatus  100 , and hence the process proceeds to a step S 203 , wherein the sheet is further inverted upside down to discharge the same out of the system, followed by terminating the present process. This operation causes the same surface of the sheet to face upward when discharged as when received from the image forming apparatus. 
         [0104]    If it is determined in the step S 202  that the sheet has not been subjected to the clear coating, the process proceeds to a step S 204  since the same surface of the sheet remains to face upward as when received from the image forming apparatus, and hence the process proceeds to a step S 204 , wherein the normal discharge (straight discharge without sheet inversion) is carried out, followed by terminating the present process. 
         [0105]    The step S 205  is executed when the sheet received from the image forming apparatus  100  has been subjected to the single-side image formation, and it is determined whether or not the sheet has been subjected to the double-sided clear coating. If the sheet has been subjected to the double-sided clear coating, the sheet has been inverted upside down compared with when received from the image forming apparatus  100 , causing the image-bearing side of the sheet to be changed from the upper side to the lower side, and hence the process proceeds to the step S 206  to perform normal discharge, followed by terminating the present process. 
         [0106]    It should be noted that even if the sheet is subjected to single-sided image formation, double-sided clear coating can be performed. By executing the step S 06 , when discharged sheets subjected to the double-sided clear coating are sequentially stacked, they are in a state discharged in proper order. 
         [0107]    On the other hand, if it is determined that execution of single-sided clear coating or inhibition of any clear coating is requested, the process proceeds to the step S 207 , wherein the sheet is inverted upside down, and then discharged, followed by terminating the present process. 
         [0108]      FIG. 7  is a diagram of a table showing the relationship between an image formation mode of the image forming apparatus, a clear coating mode of the clear coating apparatus, and an inverted discharge operation set to the clear coating apparatus. This table summarizes settings of execution or inhibition of the inverted discharge operation performed by the outside-discharge processing of the clear coating apparatus, which are configured according to the image formation mode of the image forming apparatus and the clear coating mode of the clear coating apparatus. 
         [0109]      FIG. 8  is a diagram showing changes in the normal/reversed position of each sheet, which occur according to the present embodiment as the sheet is received from the image forming apparatus after being subjected to double-sided image formation, subjected to double-sided clear coating, and then discharged out of the system after being subjected to inverted discharge processing. 
         [0110]    The execution of the above-described processing makes it possible to discharge sheets out of the system while maintaining the proper page order, even when the clear coating apparatus  200  performs double-sided clear coating on the sheet subjected to double-sided image formation by the image forming apparatus  100 . 
         [0111]      FIG. 9  is a diagram showing changes in the normal/reversed position of each sheet, which occur according to a variation of the present embodiment as the sheet is received from the image forming apparatus after being subjected to double-sided image formation, subjected to double-sided clear coating, and then discharged out of the system. In this variation, when the sheet is subjected to double-sided image formation by the image forming apparatus  100  and clear coating by the clear coating apparatus  200 , the image forming apparatus  100  first performs image formation on each sheet in inverted page order in advance, and then discharges the sheet to the clear coating apparatus  200 . 
         [0112]    As is apparent from  FIG. 9 , when the image forming apparatus  100  is requested to execute double sided image formation and the clear coating apparatus  100  is requested to execute double-sided clear coating, by configuring the system such that the image forming apparatus performs image formation on each of sheets in inverted page order in advance, the sheets are discharged out of the system with the page order properly maintained without further inverting each sheet upside down even when the clear coating apparatus  200  performs double-sided clear coating on each sheet. 
         [0113]    Further, if the image forming apparatus has been requested to perform double-sided image formation and the clear coating apparatus  200  is not required to perform clear coating, by causing the image forming apparatus  100  to perform image formation on each of sheets in normal page order, it is possible to discharge the sheets out of the system while maintaining the proper page order, without further inverting each sheet upside down. 
         [0114]    According to this variation, by performing the above-described processing, i.e. changing the page order of each sheet to be subjected to double-sided image formation, it is possible to discharge the sheets while maintaining the proper page order. 
         [0115]    While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed the embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
         [0116]    This application claims the benefit of Japanese Patent Application No. 2006-157296, filed Jun. 6, 2006, which is hereby incorporated by reference herein in its entirety.