Abstract:
The present invention provides an image-forming device that can record an image onto a rewritable image recording medium. Prior to recording a predetermined image, the medium is set and a test image for measuring the density is recorded thereon. When the density is determined to be within an allowable range, the predetermined image is recorded under certain image recording conditions and then discharged to a discharging tray. However, should the density be outside the allowable range, the conditions are changed and another test image is recorded to the medium. If after repeated density measurements the density is not within an allowable range, the device determines that the medium is defective and discharges it to an error tray.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
         [0001]    This application claims priority under 35 U.S.C. 119 from Japanese Patent Application No. 2002-366138, the disclosure of which is incorporated by reference herein.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an image-forming device and, more particularly, to an image-forming device such as a copying machine and a printer, which can form an image on a rewritable image recording medium. The present invention also relates to an image-forming method.  
           [0004]    2. Description of the Related Art  
           [0005]    Conventionally, most image recording media, such as thermal recording paper and plain paper for a plain paper copier (PPC) used for an image forming device such as a copying machine and a printer, have not been able to be reused because an image cannot be deleted once the image is recorded thereon.  
           [0006]    Therefore, resources such as forest resources used to make paper for such media have been wasted, causing problems such as environmental damage and loss of earth resources.  
           [0007]    In order to solve the above problems, an image forming device using reusable and reversible image recording media has been proposed, wherein an image recorded on an image recording medium is deleted and another image can be recorded.  
           [0008]    For example, Japanese Patent Application Laid-Open (JP-A) No. 5-58033 has disclosed an image forming device using a reversible thermosensitive recording medium, which can rewrite an image with heat, and JP-A No. 2001-301233 has disclosed an image forming device using rewritable display recording medium which can rewrite an image with light.  
           [0009]    However, image deterioration tends to occur in the above conventional rewritable media when they are repeatedly used. Thereby, in order to obtain suitable image quality, it has been necessary to select writing conditions suitable for the characteristics of each image recording medium. Moreover, there are cases where predetermined level of image quality is not obtained even under adjusted writing conditions such as when the image recording medium is repeatedly used more than a certain number of times, and, in such a case, it is determined that the image recording medium is no longer usable.  
           [0010]    In the case of an image forming device using conventional image recording media such as thermal recording paper and paper for a PPC, the image recording medium has typically been used only once, there has been no concept that the image quality deteriorates and the medium becomes unusable, and only components of the main body of the image forming device become unusable. Accordingly, management against the deterioration of the image quality and unusable components has been comparatively easy.  
           [0011]    However, in the case of the image recording medium which can be repeatedly rewritten, there has been a problem in that it is difficult to maintain excellent image quality because there are different use histories for each image recording medium. This causes complications in the setting of the optimal image recording conditions and difficulties in determination of the end of the service time for the image recording medium.  
         SUMMARY OF THE INVENTION  
         [0012]    The present invention has been made in order to solve the above problems and its object is to provide an image forming device which can record an image on a rewritable image recording medium under optimal image recording conditions and excellent image quality can be maintained.  
           [0013]    To this end, a first aspect of the present invention is to provide an image forming device comprising a recording section for recording an image on a rewritable image recording medium; a control section for controlling the recording section so that a test image for testing the image recording medium is recorded on the image recording medium; a detection section for detecting the test image recorded on the image recording medium; and a determination section for determining whether the detection section&#39;s detection result is within an allowable range or not.  
           [0014]    According to the invention, the recording section records an image on rewritable image recording medium. The rewritable image recording medium means reversible image recording medium by which an image can be repeatedly rewritten in a visible manner, and which has a function as a memory of images and can be reused. Here, the function as a memory means a function by which recorded images can be maintained on the image recording medium after recording the images even without external action.  
           [0015]    A thermosensitive recording sheet with reversibility, which has been disclosed in the above-described JP-A No. 5-58033 and by which an image can be rewritten by use of heat, and display recording medium, which has been disclosed in the above-described JP-A No. 2001-301233 and by which an image can be rewritten by an optical signal, may be listed as such image recording medium with reversibility. Moreover, an image recording medium, which has been disclosed in, for example, JP-A No. 2001-312225 and has a configuration in which a plurality of kinds of particles with different colors and electrostatic characteristics are sealed between one pair of substrates, and, on which an image is displayed by appropriately moving the particles according to the image with means for applying the voltage between the substrates, may be included as such image recording medium with reversibility.  
           [0016]    Accordingly, for example, when the thermosensitive recording sheet with reversibility is used as the image recording medium, the recording section is configured to include thermal heads and the like provided with a plurality of heating elements corresponding to pixels. Moreover, when the display recording medium, by which an image can be rewritten by an optical signal is used as the image recording medium, the recording section is configured to include an optical output device which emits an optical signal according to an image to be recorded to the display recording medium, a voltage application section which applies the voltage according to the image to the display recording medium, and the like. Moreover, when the image recording medium with a configuration in which a plurality of kinds of particles with different colors and electrostatic characteristics are sealed between one pair of substrates is used as the image recording medium, the recording section is configured to include a voltage application section which applies the voltage according to the image between the substrates in the image recording medium.  
           [0017]    The control section controls the recording section so that the test image for testing of the image recording medium is recorded on the image recording medium. The test image is an image by which it is determined for confirmation whether an excellent image is recorded on the image recording medium or not, and, for example, an image for confirmation of density, which is one of image characteristic values, can be used as the test image. This test image is detected by the detection part. It is determined by the decision section whether the detection result in the detection section is within the allowable range or not, that is, whether an image can be recorded with excellent image quality or not.  
           [0018]    Since the test image is recorded in the rewritable image recording medium and it is determined whether the detection result of the test image is within the allowable range, the optimal image recording conditions can be set, based on the determination results. Thereby, even when images are repeatedly written on the image recording medium, excellent image quality can be maintained.  
           [0019]    Here, heat quantity supplied to heating elements in the thermal head and the like are included in the image recording conditions when the thermosensitive recording sheet with reversibility is used as the image recording medium. Moreover, when the rewritable display recording medium, on which an image can be rewritten with an optical signal, is used as the image recording medium, light quantity of the optical signal emitted to the display recording medium, the voltage applied to the display recording medium and the like are included in the image recording conditions. Moreover, the voltage applied between the substrates in the image recording medium and the like are included in the image recording conditions when the image recording medium with a configuration in which a plurality of kinds of particles with different colors and electrostatic characteristics are sealed into one pair of substrates is used as the image recording medium.  
           [0020]    Here, the control section controls the recording section so that before a predetermined image to be recorded on the image recording medium is recorded on the image recording medium, the test image is recorded on the image recording medium, and when the detection result is outside the allowable range, image recording conditions for recording the predetermined image on the image recording medium are set based on the detection result.  
           [0021]    According to the invention, the control section controls the recording section before a predetermined image to be recorded on the image recording medium is recorded on the image recording medium, so that the test image is recorded on the image recording medium.  
           [0022]    And, image recording conditions for recording the predetermined image on the image recording medium are set, based on the detection result, when it is determined by the decision section that the detection result of the test image in the detection section is outside the allowable range. For example, when the detection result is outside the allowable range, the image recording conditions are changed, the test image is recorded again and determination is executed again in a similar manner to the above one. The above processing is repeated until the detection result is within the allowable range and image recording conditions for which the result is within the allowable range are set as image recording conditions for recording the predetermined image.  
           [0023]    Then, when the detection result is within the allowable range, the predetermined image to be recorded on the image recording medium is recorded under the image recording conditions for which the test image has been recorded.  
           [0024]    Thus, excellent image quality can be maintained even when images are repeatedly recorded because the predetermined image is recorded after adjustment of image recording conditions when the detection result of the test image is outside the allowable range.  
           [0025]    Moreover, the predetermined image is recorded on the image recording medium, based on the image recording conditions set by the control section, when the detection result is within the allowable range.  
           [0026]    Moreover, the control section controls the recording section so that the predetermined image to be recorded on the image recording medium and the test image are simultaneously recorded on the image recording medium, and sets image recording conditions for recording the predetermined image on the image recording medium, based on the detection result when the detection result is outside the allowable range.  
           [0027]    According to the invention, the control section controls the recording section so that the predetermined image and the test image to be recorded on the image recording medium are simultaneously recorded on the image recording medium. And, image recording conditions for recording of the predetermined image on the image recording medium are set, based on the detection result when it is determined by the decision section that the detection result by the detection section is outside the allowable range. For example, when the detection results are outside the allowable range, the image recording conditions are changed, the test image and the predetermined image are recorded on the same image recording medium again under the image recording conditions newly set and determination is executed again in the same manner as the above. The above processing is repeated until the detection result is within the allowable range.  
           [0028]    The test image recorded on the image recording medium is deleted when the detection result is within the allowable range. Thereby, only the predetermined image is recorded onto the image recording medium.  
           [0029]    Thus, excellent image quality can be maintained even when images are repeatedly recorded, because the test image and the predetermined image are recorded on the image recording medium again after adjustment of the image recording conditions when the detection result of the test image is outside the allowable range.  
           [0030]    Here, there may be applied a configuration in which the image recording conditions are changed and the test image and the predetermined image are recorded on another image recording medium, when the detection result is outside the allowable range. Moreover, there may be applied a configuration in which only the predetermined image is recorded on another image recording medium, when the detection result is within the allowable range.  
           [0031]    Moreover, the control section discharges the image recording medium to a discharging tray for defective media, when the detection result in the detection section is outside the allowable range even after the image recording conditions have been changed more than once and the test image is recorded and detected.  
           [0032]    According to the invention, it is determined that the image recording medium is defective when the detection result of the test image in the detection section is outside the allowable range even after the image recording conditions are repeatedly changed and the test image is recorded and detected. The image recording conditions are changed more than once within a changeable range. That is, it is determined that the image recording medium is defective when the detection result is not within the allowable range over a changeable range of image recording conditions.  
           [0033]    Furthermore, the image recording medium is configured to be discharged to a discharging tray for defective medium other than the tray on which a normal image recording medium is discharged when it is determined that the image recording medium is defective. Thereby, a state in which defective image recording medium and normal one are mixed can be prevented.  
           [0034]    The control section controls the recording section so that test images are simultaneously recorded on the image recording medium under a plurality of differing image recording conditions, and sets the image recording conditions, based on each detection result of each test image recorded under each differing image recording condition.  
           [0035]    According to the invention, the control section controls the recording section so that the test images are simultaneously recorded on the image recording medium under a plurality of different image recording conditions. The plurality of test images are detected in the detection section, respectively. Then, it is determined by the decision section whether each of the detection results is within the allowable range.  
           [0036]    Subsequently, the image recording conditions are set, based on each of detection results of the test images which have been recorded under the plurality of different image recording conditions. More specifically, for example, when there are among the above detection results a plurality of detection results which are within the allowable range, image recording conditions corresponding to the optimal detection result among the plurality of detection results are set as image recording conditions for recording the predetermined image. On the other hand, when none of the detection results is within the allowable range, it is determined that the image recording medium is defective and, the medium is discharged to, for example, the discharging tray for a defective medium.  
           [0037]    Thus, since the image recording conditions are set, based on each of the detection results of the test images which have been recorded on the image recording medium under the plurality of different image recording conditions from the beginning, the optimal image recording conditions can be quickly set.  
           [0038]    Moreover, the image recording medium is provided with storage medium on which an identification code is stored, the image forming device further comprising: a read section for reading the identification code stored on the storage medium; and a history storage section for storing histories of image recording conditions for the predetermined image recorded on the image recording medium, and histories of the detection results, wherein the control section stores the image recording conditions and the detection results in the history storage section in relation to the identification codes by the control section.  
           [0039]    According to the invention, the image recording medium is provided with storage medium on which identification codes have been stored. That is, the image recording medium is provided with storage medium in which an unique identification code representing the image recording medium has bee stored. Medium, which can be read by reading section from the outside with contact or without contact, may be used as the storage medium.  
           [0040]    The control section stores the image recording conditions under which the predetermined image have been recorded and the detection results in the history storage section of the device in relation to the identification codes read by the read section. The detection results and the image recording conditions are sequentially stored to form histories of the detection results and the image recording conditions, and the detection results and the image recording conditions can be managed for each image recording medium.  
           [0041]    Moreover, the control section sets image recording conditions for recording the predetermined image, based on the histories stored in the history storage section.  
           [0042]    According to the invention, the image recording conditions are set in the control section, based on the histories, that is the histories of the historical image recording conditions and the detection results. More specifically, a tendency of changes in the image recording conditions and the detection results is obtained and the image recording conditions are set, based on the obtained tendency. Thereby, the optimal image recording conditions can be quickly set. Moreover, it is possible to determine from the histories when the end of the service time for the image recording medium comes.  
           [0043]    Furthermore, the image recording medium is provided with a storage medium onto which the control section stores image recording conditions for the predetermined image recorded on the image recording medium and detection results.  
           [0044]    According to the invention, the image recording conditions and the detection results are recorded not in the side of the device, but in that of the image recording medium. Thereby, the historical image recording conditions and the detection results of the image recording medium can be obtained even from other devices.  
           [0045]    Moreover, the control section sets the image recording conditions for recording the predetermined image based on the image recording conditions and the detection results stored in the storage medium.  
           [0046]    According to the invention, since the image recording conditions are set, using the historical image recording conditions and the detection results, which have been stored in the history storage section of the image recording medium, the image recording conditions can be appropriately set and, at the same time, it is able to predict the end of the service time.  
           [0047]    Moreover, the detection section detects the display densities of the test image.  
           [0048]    According to the invention, for example, a test image with the highest density of the color which can be recorded is recorded in the image recording medium by the control section. Preferably, the above processing is executed for all colors which can be recorded. Then, the detection section detects the display density of the test image. Thus, since the display density is detected and the image recording conditions are set, based on the detection result, appropriate density can be maintained at any time and excellent image quality can be kept even when images are repeatedly rewritten.  
           [0049]    Moreover, an image can be rewritten on the image recording medium with an optical signal.  
           [0050]    Since images can be more quickly written with an optical signal in comparison with a case in which images are recorded on thermal recording paper, the throughput of the device can be improved.  
           [0051]    A second aspect of the present invention is to provide an image forming method comprising: recording a test image for testing rewritable image recording medium on the medium, based on predetermined image recording conditions; detecting image-characteristic values of the test image recorded on the image recording medium; and determining whether the detected image-characteristic values are within an allowable range or not.  
           [0052]    The method further comprises recording a predetermined image on the image recording medium, based on the predetermined image recording conditions, when it is determined that the detection result is within the allowable range.  
           [0053]    In addition, the method may further comprises changing the predetermined image recording conditions so that the detected image-characteristic values approach the allowable range, when it has been determined that a detection result is outside the allowable range; and recording the test image on the image recording medium, based on the changed image recording conditions.  
           [0054]    The steps of changing the image recording conditions; recording the test image on the image recording medium, based on the changed image recording conditions; detecting the image-characteristic values; and determining are repeated until it is determined that the image-characteristic values are within the allowable range.  
           [0055]    Also, the steps of: changing the image recording conditions; recording the test image on the image recording medium, based on the changed image recording conditions; detecting the image-characteristic values; and determining are repeated until a number of repetitions reaches a predetermined number.  
           [0056]    Moreover, the method further comprising storing at least one of image recording conditions for at least one image recorded on the image recording medium, and the detected image-characteristic values, wherein the predetermined image recording conditions are defined based on at least one of the stored image recording conditions and the image-characteristic values. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0057]    [0057]FIG. 1 is a schematic block diagram of an image forming device.  
         [0058]    [0058]FIG. 2 is a cross section of an image recording medium.  
         [0059]    [0059]FIG. 3 is a schematic block diagram of a recording device.  
         [0060]    [0060]FIG. 4 is a schematic block diagram of the recording device.  
         [0061]    [0061]FIG. 5 is an explanatory view of a carrying path of the image forming device.  
         [0062]    [0062]FIG. 6 is a flow chart of a control routine according to a first embodiment.  
         [0063]    [0063]FIG. 7 A and FIG. 7B are views of patches for density measurement.  
         [0064]    [0064]FIG. 8 is a flow chart of a control routine according to a second embodiment.  
         [0065]    [0065]FIG. 9 is a schematic block diagram of an image forming device according to a third embodiment.  
         [0066]    [0066]FIG. 10 A and FIG. 10 B are flow charts of a control routine according to the third embodiment.  
         [0067]    [0067]FIG. 11 is a flow chart of a control routine according to a fourth embodiment.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
     First Embodiment  
       [0068]    Hereinafter, a first embodiment of the present invention will be explained in detail, referring to drawings.  
         [0069]    [0069]FIG. 1 shows a block diagram of an image forming device  10  to which the invention is applied. As shown in FIG. 1, the image forming device  10  comprises: a control section  12 ; a recording device  14 ; an input section  16 ; a detection section  18 ; a discharging mechanism  20 ; a discharging tray  22 ; an at-error discharging tray (error tray)  24 ; a carrying mechanism  26 ; a timer  28 ; a temperature sensor  30 ; a humidity sensor  32 ; a memory  34  and the like.  
         [0070]    The input section  16  is an interface for inputting image information and the image information input by the input section  16  is output to the recording device  14  by the control section  12 .  
         [0071]    The recording device  14  operates according to an instruction from the control section  12  and an image is recorded on the rewritable image recording medium which will be described later, based on the image information input from the input section  16 . In the embodiment, a case in which an image recording medium on which an image can be rewritten by an optical signal is used as rewritable image recording medium will be explained.  
         [0072]    The image recording medium and the recording device which have been described in JP-A No. 2001-301233 described in the above “Summary of the Invention” may be used as the image recording medium and the recording device  14  in the embodiment. FIG. 2 shows a cross section of such an image recording medium  40 .  
         [0073]    As shown in FIG. 2, the image recording medium  40  is formed in a sheet shape and comprises a photo-conductive layer  44  which is a photosensitive layer, a light-shielding layer  46 , and a display layer  48 , which are inserted between a pair of substrates  42 . Moreover, the photo-conductive layer  44  comprises a electrical charge production layer  44 A, a electrical charge transport layer  44 B, and a electrical charge production layer  44 C, which are layered in this order.  
         [0074]    Each of the substrates  42  comprise, for example, a PET (Poly-Ethylene Terephthalate) film which is provided with an Indium Tin Oxide (ITO) electrode on an inner side. The display layer  48  comprises, for example, a nematic liquid crystal with positive dielectric anisotropy.  
         [0075]    [0075]FIG. 3 shows the image recording device  14  for recording an image on the image recording medium  40 . The recording device  14  is a device by which the image based on the image information input from the control section  12  is written on the image recording medium  40  with the optical signal.  
         [0076]    As shown in FIG. 3, the recording device  14  is provided with a data processing section  50 . The control section  12  outputs the image information input from the input section  16  to the data processing section  50 .  
         [0077]    The image information undergoes conversion processing in an arithmetic circuit  50 A of the data processing section  50  and is converted into an information signal, which is suitable for an optical output device  52 . That is, operation such as interpolation and reduction of data is appropriately executed so that the number of pixels of the image information is compatible with the number of pixels of the optical output devices  52 , depending on whether that of the image information is larger or smaller than the maximum number of pixels with which the optical output device  52  can execute batch exposure. More specifically, the operation of reduction in the image information is executed when the number of pixels of the image information is larger than the maximum number of pixels with which the optical output device  52  can execute batch exposure. On the other hand, the operation of interpolation of the image information is executed when the number of pixels of the image information is smaller than the maximum number of pixels with which the optical output device  52  can execute batch exposure. The information obtained by the operations is stored in a memory  50 B.  
         [0078]    Moreover, the recording device  14  is provided with the optical output device  52  which forms an optical pattern, based on an information signal, which has undergone the conversion processing in the data processing section  50 , for the optical output device  52  and emits the optical pattern.  
         [0079]    The optical output device  52  comprises a transmission type LCD (liquid crystal display)  54  which functions as an optical pattern emitting face. The transmission type LCD  54  is configured to be connected to an optical-output-device control section  56  which drives and controls the LCD  54 .  
         [0080]    An ordinary LCD-backlight  58  having an optical waveguide and a cold-cathode tube waveguide at the end of the waveguide is provided at the back of the transmission type LCD  54 . The backlight  58  is connected to a backlight control circuit  60  by which drives and controls the backlight  58 .  
         [0081]    And, a two-dimensional microlens array  62  is arranged on the upper side of the transmission type LCD  54 . The two-dimensional microlens array  62  is located by spacers (not shown) so that an optical pattern which is formed on the transmission type LCD  54  based on the information signal for the optical output device, is focused on the surface of the photoconductive layer  44  in the image recording medium  40 .  
         [0082]    Particularly, since a transparent support plate  64  is put on the spacers, over which the image recording medium  40  is arranged, so that the upper side of the two dimensional microlens array  62  is covered by the transparent support plate  64 . Thus, the focus is spontaneously adjusted by setting the image recording medium  40  in tight contact with the transparent support plate  64 . Here, the image recording medium  40  is arranged on the transparent support plate  64  so that the substrate  42  nearer to the photoconductive layer  44  in the image recording medium  40  and the transparent support plate  64  are opposing to each other.  
         [0083]    When the photoconductive layer  44  and the display layer  48  are used together for a configuration of the image recording medium  40 , the recording device  14  and the image recording medium  40  are electrically connected to each other and the means for applying voltage to an ITO electrode formed on the substrate  42  of the image recording medium  40  is required. Accordingly, a voltage application section  66  is provided in the recording device  14 .  
         [0084]    The voltage application section  66  is configured to apply a voltage pulse, which is required to drive the display layer  48  of the image recording medium  40 , to the above ITO electrode at timing in synchronization with that of the optical output device  52  in the recording device  14 . The voltage pulse is generated in a power supply  56 B including an AC power supply and a DC power supply. Here, the ITO electrode formed on the substrate  42  of the image recording medium  40  and the voltage application section  66  are detachable.  
         [0085]    The voltage pulse may be generated by voltage transformation and shaping of voltage wave, based on the AC power supply, or by manual ON/OFF switching of the DC power supply which is supplied from a battery such as electric cells. Furthermore, a pulse with a required wave form may be generated from the DC power supply, using a switching circuit. For example, a circuit, which comprises a wave-form storage section like a ROM, a D/A conversion section and a control section may be used for the above pulse generation. In th circuit, a wave form read out from the ROM at application of the voltage undergoes D/A conversion. And, means for generating a pulse by a method like an electric circuit such as a pulse generating circuit can be used. In addition, in order to set the timing of the voltage application section  66  and the exposure timing of the optical output device  52  in synchronization with each other, the voltage may be applied to the image recording medium  40 , based on an electric trigger detecting an exposure state and a driving state of the optical output device  52 .  
         [0086]    Hereinafter, one specific example of the recording device  14  will be explained, referring to FIG. 4.  
         [0087]    A rectangular opening  70  is provided on the upper side of a box- type case  68  of the recording device  14  and a transparent glass plate  72  is fitted into the opening  70  to form a display window  74 . The inside of the case  68  is divided into two layers of upper and lower layers, among which the lower layer forms a media storing section  76  which stores the later-descried image recording medium  40 . An discharging slot  78  from which the image recording medium  40  is discharged is provided at the one end (the left end in FIG. 4) of the media storing section  76  and a feed roller  80  is arranged near the discharging slot  78 . Moreover, the image recording medium  40  in the media storing section  76  can be taken out by the driving power of the feed roller  80  one by one.  
         [0088]    On the other hand, the optical output device  52  which displays an image is provided in the upper layer of the case  68 . That is, the backlight  58  and the like are provided in the upper layer of the case  68 . Moreover, arrangement space  82  for the image recording medium  40  is provided just under the transparent glass plate  72  and two pairs of carrying rollers  84 ,  86  are provided at the both ends of the arrangement space  82 , respectively. A loading slot  88  and a discharging slot  90  of the image recording medium  40  are provided on the side walls near the pairs of the carrying rollers  84 ,  86 .  
         [0089]    The image recording medium  40  taken out from the media storing section  76  is loaded through the not-shown carrying mechanism into the loading slot  88  in the direction of the arrow A shown in FIG. 4. Thereby, the image recording medium  40  is positioned in the arrangement space  82  in an approximately parallel state to the transparent glass plate  72 , by being carried by driving force of the pair of carrying rollers  84 . Under such a state, the optical output device  52  is controlled by the optical-output-device control section  56 , based on the input image information and, at the same time, light corresponding to the image is exposed to the image recording medium  40  by applying of the voltage to the image recording medium  40  with the voltage application section  66  to form the image.  
         [0090]    The image recording medium  40  on which the image has been recorded is discharged from the discharging slot  90  by the driving force of the pair of carrying rollers  86  at the right side in a state with the image is displayed.  
         [0091]    Though the details will be described later, the image recording medium  40  discharged from the recording device  14  is carried to the position of the detection section  18 , as shown in FIG. 5, and a test image recorded on the image recording medium  40  is detected if necessary. And, a carrying path of the image recording medium  40  is switched by a path switching mechanism  92  according to a detection result.  
         [0092]    The path switching mechanism  92  switches the carrying path of the image recording medium  40  to a carrying path  94 A or  94 B. When the carrying path  94 A is selected, the image recording medium  40  is carried again into the recording device  14  by the driving force of pairs of carrying rollers  95 ,  96 . When the carrying path  94 B is selected, the image recording medium  40  is carried into the discharging mechanism  20  and is discharged to either the discharging tray  22  or the error tray  24  according to the detection result. Here, the path switching mechanism  92 , the pairs of carrying rollers  95 ,  96 , and the like form a part of the carrying mechanism  26 .  
         [0093]    The detection section  18  includes a density sensor which can detect spectral reflection densities of colors such as white, black, yellow, magenta, cyan, red, green, and blue.  
         [0094]    The timer  28  is provided to get the current time. The function of the temperature sensor  30  is to detect the temperature around the device. The humidity sensor  32  is installed for detection of the humidity around the device. The memory  34  is provided to store a later-described control-routine program and various kinds of data.  
         [0095]    Here, the control section  12  corresponds to a control section and a decision section in the invention, the recording device  14  corresponds to a recording section of the invention, the detection section  18  corresponds to a detection section of the invention and the error tray  24  corresponds to a discharging tray for defective medium in the invention.  
         [0096]    Then, the control routine to be executed in the control section  12  will be explained as an operation of the embodiment, referring to a flow chart shown in FIG. 6.  
         [0097]    In the first place, a value of a counter C which counts how many times the later-described density measurement has been executed is initialized at STEP  100 . Here, ‘1’ is assigned for the value of the counter C.  
         [0098]    The carrying mechanism  26  is controlled at STEP  102  so that the image recording medium  40  is moved from the media storing section  76  and is set in the arrangement space  82 .  
         [0099]    The recording device  14  is controlled at STEP  104  so that a test image including patches W, BK for density measurement of white and black as shown in FIG. 7(A) is recorded on the image recording medium  40 , if an image to be recorded is a monochrome image. Here, if an image to be recorded is a color image, the recording device  14  is controlled so that a test image including patches Y, M, C for density measurement of yellow, magenta, and cyan in addition to the patches W, BK for density measurement of white and black as shown in FIG. 7 (B) is recorded on the image recording medium  40 . The recording device  14  records the test image on the image recording medium  40  under predetermined image recording conditions. In the embodiment, the image recording conditions are the voltage applied by the voltage application section  66  to the image recording medium  40  and the quantity of light of the optical pattern output from the optical output device  52  outputs.  
         [0100]    More specifically, the control section  12  outputs the image information about the test image as shown in FIG. 7(A) to the recording device  14 , and instructs recording the test image. Thereby, the image information about the test image is input to the data processing section  50  and is stored in the memory  50 B after predetermined operations are executed in the arithmetic circuit  50 A. Then, the driving circuit  56 A in the optical-output-device control section  56  reads an information signal for the optical output device from the memory  50 B in the data processing section  50 .  
         [0101]    Subsequently, the driving circuit  56 A supplies a driving signal and a lighting signal respectively to the transmission type LCD  54  and the backlight  58  in the optical output device  52  according to the information signal for the optical output device. Here, there is set a configuration in which, once the backlight  58  is lighted, lighting is continued during set time until a SWITCH-OFF signal is input. Accordingly, SWITCH-ON/OFF is not executed when an optically written image is updated.  
         [0102]    As described above, the optical output device  52  emits the optical pattern corresponding to the test image by driving the transmission type LCD  54  and the backlight  58 . Thereby, the optical pattern corresponding to the test image is in a state in which the pattern is irradiated on the photoconductive layer  44  of the image recording medium  40 . However, the voltage is not supplied to the ITO electrode formed on the inside of the substrate  42  in the image recording medium  40  and the image has not been reproduced at this stage.  
         [0103]    Then, the predetermined voltage (for example, the bias voltage pulse of a rectangular wave) is applied to an electrode terminal of the image recording medium  40  by the voltage application section  66 . When the predetermined voltage is applied, the reflective image according to the optical pattern is recorded on the display layer  48  of the image recording medium  40 . In detail, when the voltage is applied (the bias voltage pulse is supplied), impedance change corresponding to an exposure pattern from the optical output device  52  is generated in the photoconductive layer  44 . And, there is a state in which the voltage is selectively applied on the display layer  48  laminated on the photoconductive layer  44  on which the impedance change has been generated. Under such a state, application of the voltage to the whole image recording medium  40  is released and the exposure by the optical output device  52  is completed. The test image is recorded on the display layer  48  of the image recording medium  40  after completion of the exposure and release of the voltage application as a reflective image according to the exposure pattern. The image recording medium  40  on which the test image has been recorded has the function as the memory, and even when the terminal for voltage application is removed, the display contents can be maintained without an electric source, the medium  40  being separated from the recording device  14 .  
         [0104]    The image recording medium  40  on which the test image has been recorded is carried by the carrying mechanism  26  to the position of the detection section  18  and stopped at the position.  
         [0105]    The detection section  18  is controlled at STEP  106  so that the densities of the patches for density measurement are detected by the detection section  18 .  
         [0106]    Subsequently, it is determined for each patch for density measurement at STEP  108  whether the measured densities are within an allowable range or not. Then, the processing proceeds to STEP  110  when all of the measured densities are within the allowable range. The processing proceeds to STEP  114  when any one of the measured densities for the colors is outside the allowable range.  
         [0107]    The recording device  14  is controlled at STEP  110  so that the predetermined image to be recorded in the image recording medium  40  is recorded therein. That is, the predetermined image is recorded in the image recording medium  40  by the same processing as that of the test image. Here, since the predetermined image replaces the test image, the test image will not be left on the image recording medium  40 .  
         [0108]    Subsequently, the path switching mechanism  92  and the discharging mechanism  20  are controlled at STEP  112  so that the image recording medium  40  on which the predetermined image has been recorded is discharged to the discharging tray  22  for a normal image recording medium  40 . That is, the path switching mechanism  92  is controlled so that the carrying path  94 B is selected. Thereby, the image recording medium  40  on which the predetermined image has been recorded is carried on the carrying path  94 B. Then, the discharging mechanism  20  is controlled to discharge the image recording medium  40  to the discharging tray  22 .  
         [0109]    On the other hand, it is determined at STEP  114  whether the value of the counter C is larger than a threshold or not. When the value of the counter C is not smaller than the threshold value, it is decided that the image recording medium  40  is no longer usable.  
         [0110]    Then, the processing proceeds to STEP  116  when the value of the counter C is not smaller than the threshold value and the processing proceeds to STEP  118  when the value of the counter C is smaller than the threshold value.  
         [0111]    It is determined that the image recording medium  40  comes to the end of the service time, and the path switching mechanism  92  and the discharging mechanism  20  are controlled at STEP  116  so that the image recording medium  40  is discharged to the error tray  24 . Thereby, the image recording medium  40  which comes to the end of the service time is discharged to the discharging tray which is different from a tray for a normal image recording medium  40 . Then, the processing returns to STEP  100  and the above described processing is executed for another image recording medium.  
         [0112]    On the other hand, the image recording conditions such as the quantity of light which the optical output device  52  outputs and the value of the voltage which the voltage application section  66  outputs are adjusted at STEP  118 . That is, the quantity of light which the optical output device  52  outputs and the value of the voltage which the voltage application section  66  outputs are adjusted to increase the measured density when the density is lower than the allowable range, and the quantity of light which the optical output device  52  outputs and the value of the voltage which the voltage application section  66  outputs are adjusted to reduce the measured density when the density is higher than the allowable range. Here, there may be applied a configuration in which a look-up table defining a relation between the image recording conditions and the densities has been stored in the memory  34  beforehand and the image recording conditions may be changed according to the look-up table.  
         [0113]    The value of the counter C is incremented at STEP  120  and the processing returns to STEP  104 . Thereby, the above described density measurement is executed under new image recording conditions. Then, the image recording medium  40  is discharged to the discharging tray  22  when all of the measured densities for the colors are within the allowable range and the image recording medium  40  is discharged to the error tray  24  when any one of the measured densities for the colors is outside the allowable range.  
         [0114]    Thus, before the predetermined image is recorded, the test image is recorded, and the density of the test image is detected to determine whether the densities are within the allowable range or not. The predetermined image is recorded when it is within the allowable range. Accordingly, the optimal image recording conditions can be set, based on the determination result. Thereby, images are repeatedly written on the image recording medium  40  and excellent image quality can be maintained even when the characteristics of the image recording medium  40  have changed.  
         [0115]    The embodiment has been described above in which the image is recorded on the image recording medium according to an optical signal. But the image recording medium is not limited to the above one and the invention can be applied to any kind of rewritable image recording medium. For example, when rewritable thermal recording paper is used, the predetermined image may be recorded after the test image is deleted. In this case, the heat quantity supplied to a thermal head is the image recording condition.  
       Second Embodiment  
       [0116]    Subsequently, a second embodiment according to the invention will be explained. Here, parts similar to those previously described with reference to the first embodiment are denoted by the same reference numbers, and detailed description will be eliminated.  
         [0117]    Because an image forming device according to the second embodiment is the same as the image forming device  10  which has been explained in the first embodiment, the explanation will be eliminated.  
         [0118]    A control routine, which is executed as an action of the embodiment in a control section  12 , will be explained, referring to a flow chart shown in FIG. 8. Here, steps for processing similar to those in the flow chart in FIG. 6 are denoted by the same reference numbers, and only different steps will be explained.  
         [0119]    In the embodiment, the value of a counter C is initialized at STEP  100  and the image recording medium  40  is set at STEP  102 . Not only a test image, but also a predetermined image are recorded on an image recording medium  40  at the same time at STEP  104 A.  
         [0120]    Then, when it is determined at STEP  108  that all of the measured densities for the colors are within the allowable range, a recording device  14  is controlled so that only the test image is deleted at STEP  110 A.  
         [0121]    As described above, since the test image and the predetermined image are recorded at the same time, only deletion of the test image is required when the densities are within the allowable range.  
       Third Embodiment  
       [0122]    Now, a third embodiment of the invention will be explained. Here, parts similar to those previously described with reference to the above embodiments are denoted by the same reference numbers, and the detailed description will be eliminated. In the embodiment, a case in which an image recording medium  40  is provided with a storage medium in which an ID has been stored as an identification code will be explained.  
         [0123]    [0123]FIG. 9 shows an image forming device  11  according to the embodiment. The image forming device  11  shown in FIG. 9 is provided with a read section  99  for a reading function. Since other components are similar to those of the image forming device  10  shown in FIG. 1, the explanation will be eliminated.  
         [0124]    The image recording medium  40  is provided with a storage medium  40 A in which a unique ID has been stored and the read section  99  can read ID stored in the storage medium  40 A using the contactless technique such as radio communication.  
         [0125]    Moreover, though the details will be described later, historical measured density-data are stored in a memory  34  for a history storage section as a history in relation to IDs.  
         [0126]    Then, a control routine, which is executed as an action of the embodiment in a control section  12 , will be explained, referring to a flow chart shown in FIGS. 10A and 10B.  
         [0127]    The value of the counter C is initialized at STEP  200  and a carrying mechanism  26  is controlled at STEP  202  in such a way that the image recording medium  40  is moved from a media storing section  76  and located in a arrangement space  82 .  
         [0128]    The read section  99  is controlled at STEP  204  in such a way that an ID stored in the storage medium  40 A of the set image recording medium  40  is read.  
         [0129]    It is determined at STEP  206  whether there is historical measured data corresponding to the read ID in the memory  34  or not. Then, the processing proceeds to STEP  210  when there is the historical measured data, and the processing proceeds to STEP  224  when there has been no historical measured data.  
         [0130]    The image recording conditions are set at STEP  210 , based on the historical measured data, that is, the history. Here, measurement data include measured density values, image recording conditions, dates that measurement have been conducted, temperatures, humidity values and the like.  
         [0131]    The image recording conditions are set, using the above measured data. For example, the previous image recording conditions may be set as the current image recording conditions, or the current image recording conditions may be determined based on a tendency of changes in the historical image recording conditions. On the other hand, image recording conditions which has been defined beforehand are set for an initial image recording conditions at STEP  224 .  
         [0132]    Then, a test image is recorded on the image recording medium  40  at STEP  212  under the set image recording conditions.  
         [0133]    A detection section  18  is controlled at STEP  214  in such a way that the densities of patches for density measurement recorded on the image recording medium  40  are detected by the detection section  18 .  
         [0134]    Subsequently, it is determined with regard to each patch for density measurement at STEP  216  whether the measured densities are within an allowable range or not. Then, the processing proceeds to STEP  218  when all the measured densities are within the allowable range, and the processing proceeds to STEP  226  when any one of the measured densities for each color is outside the allowable range.  
         [0135]    The recording device  14  is controlled at STEP  218  in such a way that a predetermined image to be recorded in the image recording medium  40  is recorded.  
         [0136]    Subsequently, a date on which the above recording is executed is acquired by a timer  28 , a value of temperature at the recording is acquired by a temperature sensor  30  and a value of humidity at the recording is acquired by a humidity sensor  32  at STEP  220 . Then, the above data, image recording conditions at the recording, measured density values and the like are stored as measurement data in the memory  34  in relation to IDs.  
         [0137]    Then, a path switching mechanism  92  and a discharging mechanism  20  are controlled at STEP  222  in such a way that the image recording medium  40  on which the predetermined image has been recorded is discharged to a discharging tray  22  to which a normal image recording medium is discharged. Thereby, the image recording medium  40  is discharged to the discharging tray  22 .  
         [0138]    On the other hand, it is determined at STEP  226  whether a value of the counter C is larger than a threshold or not. Then, the processing proceeds to STEP  228  when the value of the counter C is larger than the threshold value. The processing proceeds to STEP  230  when the value of the counter C is smaller than the threshold value.  
         [0139]    It is determined that the image recording medium  40  comes to the end of the service time, and the path switching mechanism  92  and the discharging mechanism  20  are controlled at STEP  228  in such a way that the image recording medium  40  is discharged to an error tray  24 . Thereby, the image recording medium  40  which comes to the end of the service time is discharged to the error tray  24 . Then, the processing returns to STEP  200  and the similar series of processing to the above ones are executed for another image recording medium.  
         [0140]    On the other hand, the image recording conditions, that is, the quantity of light which an optical output device  52  outputs and the value of the voltage which a voltage application section  66  outputs are adjusted at STEP  230 . That is, the quantity of light which the optical output device  52  outputs and the value of the voltage which the voltage application section  66  outputs are adjusted to increase the densities when the measured densities are lower than the allowable range, and the quantity of light which the optical output device  52  outputs and the value of the voltage which the voltage application section  66  outputs are adjusted to reduce the densities when the densities are higher than the allowable range.  
         [0141]    The value of the counter C is incremented at STEP  232  and the processing returns to STEP  212 . Thereby, a test image is recorded under new image recording conditions and the density measurement is executed in a similar manner to the above-described one. The image recording medium  40  is discharged to the discharging tray  22  when all of the measured densities for the colors are within the allowable range and the image recording medium  40  is discharged to the error tray  24  when any one of the measured densities for the colors is outside the allowable range.  
         [0142]    As described above, since image recording conditions are set, based on historical measured data, optimal image recording conditions can be quickly set and the throughput of the device can be improved.  
         [0143]    Here, though there has been explained in the above description a configuration in which the measured data is stored in the memory  34  at the side of the device, the data may be configured to be stored in the storage medium  40 A of the image recording medium  40 . In this case, the historical measured data is read from the storage medium  40 A and image recording conditions may be set, based on the measured data. Moreover, only the previous measured data may be configured to be stored in the storage medium  40 A when the storage capacity of the storage medium  40 A is small. In this case, the image recording conditions which has been stored in the storage medium  40 A may be set as the current image recording conditions.  
         [0144]    Moreover, there may be a configuration in which a test image and a predetermined image are recorded at the same time, and the test image may be deleted later when the densities become within the allowable range.  
       Fourth Embodiment  
       [0145]    Then, a fourth embodiment of the invention will be explained. Here, parts similar to those previously described with reference to the above embodiments are denoted by the same reference numbers, and the detailed description will be eliminated. An image forming device according to the fourth embodiment is the same as the image forming device  11  which has been explained in the third embodiment, the explanation will be eliminated.  
         [0146]    Subsequently, a control routine, which is executed as an action of the embodiment in a control section  12 , will be explained, referring to a flow chart shown in FIG. 11. Here, steps for processing similar to those in the flow chart in FIGS. 10A and 10 B are denoted by the same reference numbers, and only different steps will be explained.  
         [0147]    An image recording medium  40  is set at STEP  202 , an ID is read from a storage medium  40 A of the image recording medium  40  at STEP  204 , the historical measured data corresponding to the ID is searched in a memory  34  at STEP  206 . It is determined at STEP  208  whether there is the historical measured data or not.  
         [0148]    It is determined whether the historical measured data is existed in the memory  34  or not. Then, when the historical measured data exists, a plurality of different image recording conditions are set at STEP  210 A, based on the historical measured data. For example, other image recording conditions may be set, centering on the previous image recording conditions, or other image recording conditions may be set, centering on seemingly optimal image-recording-conditions which are obtained on the basis of a tendency of changes in the historical image recording conditions. On the other hand, when the historical measured data does not exist, a plurality of predetermined image recording conditions are set for the initial image recording conditions at STEP  224 A.  
         [0149]    Subsequently, a test image is recorded at STEP  212  on the image recording medium  40  under one image recording condition which has been selected from a plurality of set image recording conditions.  
         [0150]    A detection section  18  is controlled at STEP  214  so that the densities of patches for density measurement are detected by the detection section  18 .  
         [0151]    It is determined at STEP  215  whether the density measurement has been executed for all the image recording conditions or not. When the density measurement has been executed for all the image recording conditions, the processing proceeds to STEP  217 , and the processing proceeds to STEP  219  when the density measurement has not been executed for any one of the image recording conditions.  
         [0152]    The image recording conditions are changed at STEP  219  to image recording conditions which are different from the measured image recording conditions and under which measurement has not been executed. Subsequently, the processing proceeds to STEP  212 . Thereby, a test image is recorded under other image recording conditions and the density measurement is executed. The above processing is repeated until the density measurement is completed for all the image recording conditions.  
         [0153]    Subsequently, when the density measurement is completed for all the image recording conditions which have been set, it is determined at STEP  217  whether any one of measured densities is within an allowable range or not. The processing proceeds to STEP  218  when any one of measured densities is within the allowable range, and the processing proceeds to STEP  228  when all the measured densities are not within the allowable range.  
         [0154]    A recording device  14  is controlled at STEP  218  in such a way that a predetermined image is recorded on the image recording medium  40  under image recording conditions on which the densities are within the allowable range. Here, when there are a plurality of image recording conditions on which the densities are within the allowable range, the most appropriate image recording condition is adopted from the plurality of the image recording conditions.  
         [0155]    Subsequently, a date on which the above recording is executed is acquired by a timer  28 , a value of temperature at the recording is acquired by a temperature sensor  30  and a value of humidity at the recording is acquired by a humidity sensor  32  at STEP  220 . Then, the data, image recording conditions at the recording, measured density values and the like are stored as measurement data in the memory  34  in relation to IDs.  
         [0156]    Subsequently, a path switching mechanism  92  and a discharging mechanism  20  are controlled at STEP  222  in such a way that the image recording medium  40  on which the predetermined image has been recorded is discharged to a discharging tray  22  for the normal image recording medium  40 . Thereby, the image recording medium  40  is discharged to the discharging tray  22 .  
         [0157]    It is decided that the image recording medium  40  comes to the end of the service time, and the path switching mechanism  92  and the discharging mechanism  20  are controlled at STEP  228  in such a way that the image recording medium  40  is discharged to an error tray  24 . Thereby, the image recording medium  40  which comes to the end of the service time is discharged to the error tray  24 . Then, the processing returns to STEP  202 , at which similar series of processing to the above ones are executed for another image recording medium.  
         [0158]    Thus, since a plurality of image recording conditions are set, based on the historical measured data, density is measurement is executed, and an image is recorded after selecting the optimal image recording condition considering the measured results, the optimal image recording condition can be more quickly set in comparison with a case in which image recording conditions are changed until measured densities becomes within the allowable range. Thereby, the throughput of the device can be improved.  
         [0159]    Moreover, though the measured data is configured to be stored in the memory  34  at the side of the device in the above embodiment, the data may be configured to be stored in the storage medium  40 A of the image recording medium  40 . In this case, the historical measured data is read from the storage medium  40 A and a plurality of image recording conditions may be set, based on the measured data. Moreover, only the previous measured data may be configured to be stored in the storage medium  40 A when the storage capacity of the storage medium  40 A is small. In this case a plurality of image recording conditions may be set, centering on image recording conditions which have been stored in the storage medium  40 A.  
         [0160]    Moreover, there may be a configuration in which a test image and a predetermined image are recorded at the same time and the test image may be deleted later when the densities become within the allowable range.  
         [0161]    As explained above, the invention has an excellent advantage that an image is recorded on a rewritable image-recording medium under the optimal image recording condition and preferable image quality can be maintained.