RU2574525C2 - Device to generate images - Google Patents

Abstract

FIELD: printing industry.

SUBSTANCE: invention relates to an image generation device provided by a function of colorimetric value measurement. The proposed image generation device comprises an image generation unit, configured as capable of image generation on a printed carrier, a fixing unit, configured with the possibility to fix the image on a printed carrier, a transportation unit configured as capable of printed carrier transportation along a transportation track and variation of printed carrier transportation direction, which passes via the fixing unit, to a reverse one, a colour measurement unit configured as capable of measuring, after the fixing unit in direction of printed carrier transportation, the image colour fixed on the printed carrier, and a control unit configured as capable of controlling the transportation unit so that the time interval from the moment, when the edge of the printed carrier passes via the fixing unit, until the moment, when the specified edge of the printed carrier, transportation direction of which is changed to reverse, passes via the colour measurement unit measurement position, in case when the colour measurement unit measures the image colour fixed on the printed carrier, was more than the time interval from the moment, when the edge of the printed carrier passes via the fixing unit, until the moment, when the specified edge of the printed carrier, the transportation direction of which is changed to reverse, passes via the colour measurement unit measurement position, in case, when the colour measurement unit does not measure the colour of the image fixed on the printed carrier.

EFFECT: provision of an image generation device, capable of achieving high-accuracy matching of colours and colour stability.

15 cl, 34 dwg

Description

FIELD OF THE INVENTION

[0001] The present invention relates to an image forming apparatus provided with a colorimetric value measuring function.

BACKGROUND OF THE INVENTION

[0002] Typical image quality parameters in image forming apparatuses include graininess, two-dimensional uniformity for an image, letter quality and color reproducibility (including color stability), and the like. for one page. Nowadays, when multicolor imaging devices are widely used, it is sometimes said that the most important image quality is color reproducibility. Based on life experience, a person has memories of the expected colors (especially human skin, blue sky, metal, etc.), and he may feel uncomfortable if the color is outside the acceptable expected range. Such colors are called memory colors, and their reproducibility is considered increasingly important when displaying photographs or the like. As for not only photographic images, but also document images, among users in offices who feel uncomfortable due to differences in color reproduction of monitors, namely users working in the areas of technology related to graphics, who are interested in the reproducibility of color images CG (computer graphics), the need for reproducible colors (including stability) is growing on demand imaging devices.

[0003] To fulfill the user need for reproducibility of colors, Japanese Patent Laid-Open No. 2004-086013 proposes an image forming apparatus for reading an insert image (measurement image) formed on a print medium using a color sensor provided on the transport path of the print medium. Compared to a standalone colorimetric meter that reads an image insert on a print medium externally output by an image forming apparatus, the invention disclosed in Japanese Patent Laid-Open No. 2004-086013 has the advantage of being able to automatically create an ICC profile . "ICC" is the abbreviation of the International Color Consortium. By means of a color management module (CMM) that performs color conversion using the ICC profile, color matching between a plurality of imaging devices or between an imaging device and an image display device can be achieved.

[0004] However, when using the invention from Japanese Patent Laid-Open No. 2004-086013, the problem of a phenomenon called “thermochromism” in which the color of the measurement image, which should be the measurement target, changes under the influence of temperature, is due to that the color sensor is located on the transport route next to the fixing device. This is a phenomenon caused by the fact that the molecular structure that forms the coloring matter, such as toner or ink, changes due to the effect of “heating” or the like.

[0005] In order to measure the colorimetric value of the measurement image in the image forming apparatus, it is necessary that the device is in a state where the ink is applied to the recording medium and the color mixing is completed. When using an image forming apparatus in which ink is used as a coloring matter, it is necessary to measure the colorimetric value after heating and drying the ink in the drying apparatus. When using an image forming apparatus in which toner is used as a coloring matter, it is necessary to measure the colorimetric value after mixing colors by heating and melting the toner using a fixing device. The reason is that a user who needs to maintain color accuracy or color stability usually draws conclusions based on the image under normal temperature conditions. Accordingly, the color sensor should be located on the side after the drying means or fixing device in the direction of transporting the sheets.

[0006] Moreover, in order to create a compact configuration of the image forming apparatus, the length of the transport route from the drying means or fixing device to the color sensor should be the minimum length. Accordingly, the sheet and the coloring matter, heated by means of a drying means or fixing device, are transported to the color sensor without cooling to normal temperature. In addition, the temperature of the recording medium also becomes higher than normal temperature due to the increasing temperature of the internal components of the image forming apparatus, such as the transport guide of the recording medium or the air inside the device.

[0007] As described above, in some cases, the image forming apparatus within which the color sensor is provided is susceptible to thermochromism and therefore obtains a colorimetric value measurement other than color under normal conditions (under normal temperature conditions). There are also cases where it is not possible to meet the requirements of the color matching standard, which is an index of color matching accuracy and color stability, and the reproducibility standard, which is the stability standard in accordance with ISO 12647-7.

SUMMARY OF THE INVENTION

[0008] The present invention provides an image forming apparatus capable of eliminating a thermochromism phenomenon in which the color of a measurement image changes due to a temperature that achieves high-precision color matching and color stability.

[0009] The present invention provides an image forming apparatus including: image forming means for forming an image on a print medium using a coloring matter; fixing means for fixing the image on the print medium; means for measuring colorimetric values (color measuring means) for measuring, after fixing means in the direction of transportation of the print medium, the colorimetric value (color) of the image recorded on the print medium; and control means for setting a period of time from the moment when the recording medium passes through the fixing means to the moment when the colorimetric value is measured by the means of measuring the colorimetric value when the measurement of the colorimetric value is carried out by the means of measuring the colorimetric value longer than the period of time taken for transporting the printing medium from the fixing means to the means for measuring the colorimetric value in the case when The determination of the colorimetric value is not performed by the means of measuring the colorimetric value.

[0010] According to the present invention, the temperature of the recording medium is reduced sufficiently by stopping the recording medium on the output path, transporting the recording medium at a low speed, or switching the transport path. If the temperature of the recording medium can be sufficiently reduced, the phenomenon of thermochromism is eliminated. As a result, it is possible to provide an image forming apparatus capable of achieving high-precision color matching and color stability.

[0011] In addition, characteristic features of the present invention will become apparent from the following description of illustrative embodiments (with reference to the accompanying drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a graphical representation showing an image forming apparatus;

[0013] FIG. 2 is a graphical representation showing a color sensor;

[0014] FIG. 3 is a graphical representation showing a control unit;

[0015] FIG. 4 is a graphical representation depicting an ICC profile;

[0016] FIG. 5 is a graphical representation depicting a color management environment;

[0017] FIG. 6 is a flowchart depicting a first embodiment;

[0018] FIGS. 7A-7C are schematic diagrams depicting waiting positions in a first embodiment;

[0019] Fig. 8 is a diagram depicting the relationship between a waiting period of a recording medium, a surface temperature of the recording medium and ΔE76 (comparison is based on 15 ° C);

[0020] FIG. 9 is a diagram depicting a possible temperature range of a recording medium in an image forming apparatus;

[0021] FIG. 10 is a graphical representation showing an example of a cooling time period for each type of recording medium;

[0022] FIGS. 11A and 11B are diagrams depicting an intermediate accumulator (buffer) from a second embodiment;

[0023] FIG. 12 is a flowchart depicting a second embodiment;

[0024] FIG. 13 is a diagram depicting the relationship between a period of time for a printing medium, a surface temperature of a paper, and ΔE76 (comparison is based on 15 ° C);

[0025] FIG. 14 is a block diagram depicting a system configuration of an image forming apparatus;

[0026] FIG. 15 is a diagram depicting a color change trend of each coloring matter;

[0027] FIG. 16 is a diagram depicting a trend in optical density of each coloring matter;

[0028] FIGS. 17A-17C are diagrams showing spectral reflection coefficient data at each temperature in a time period when the colorimetric value of the magenta insert image is measured by a color sensor;

[0029] FIGS. 18A and 18B are diagrams depicting filter sensitivity properties used in optical density calculation processing;

[0030] FIG. 19 is a flowchart depicting the operation of an image forming apparatus;

[0031] FIG. 20 is a flowchart depicting operation for adjusting a maximum optical density;

[0032] FIG. 21 is a flowchart depicting an operation for adjusting tones;

[0033] FIG. 22 is a flowchart depicting an operation for multicolor correction processing;

[0034] FIG. 23 is a flowchart depicting an operation for performing target value calculation processing;

[0035] FIG. 24 is a table showing a comparison between effects of an embodiment and an example;

[0036] FIG. 25 is a flowchart depicting the operation of an image forming apparatus;

[0037] FIG. 26 is a flowchart depicting multi-color correction processing;

[0038] FIGS. 27A and 27B are schematic diagrams illustrating print media setting screens;

[0039] FIG. 28 is a graphical representation depicting a fixing condition for each mode;

[0040] FIG. 29 is a graphical representation showing modes for combinations of bulk and gloss recycled paper;

[0041] FIG. 30 is a graphical representation depicting modes for combinations of bulk and gloss of high quality paper;

[0042] FIG. 31 is a graphical representation depicting modes for combinations of bulk and gloss coated paper;

[0043] FIG. 32 is a graphical representation showing modes for combinations of bulk and gloss recycled paper;

[0044] FIG. 33 is a graphical representation showing modes for combinations of bulk and gloss of high quality paper; and

[0045] FIG. 34 is a graphical representation showing modes for combinations of bulk and gloss coated paper.

DESCRIPTION OF EMBODIMENTS

[0046] In the present invention, the period of time from the moment when the recording medium passes through the fixing unit to the moment when the colorimetric value is measured by the colorimetric value measurement unit in the case where the colorimetric value measurement is performed by the colorimetric value measurement unit is set to be longer, than the time period taken for transporting the print medium from the installation unit to the colorimetric value measurement unit in the case, g de measurement of the colorimetric value is not performed by the measurement unit of the colorimetric value. In particular, a feature of the first embodiment is the control of the transport speed of the recording medium in the transport route (for temporarily setting the transport speed to zero). A feature of the second embodiment is the installation of a longer transportation length by switching the transportation route. Note that in the second embodiment, the transportation speed can be reduced in part of the transportation route when a sufficient transportation length cannot be ensured, even if the transportation route is switched. In both embodiments, there is a feature of causing the printing medium to arrive at the colorimetric measurement unit after the time period elapsing from the time period when the printing medium passes through the fixing unit exceeds the prescribed time period by controlling the route transportation or transportation speed. In this case, the prescribed time period is the time period when the color difference ΔE76 obtained by the colorimetric value measuring unit at a temperature in the environment where the image forming apparatus is installed is 1.5 or less. In other words, the prescribed period of time is a period of time in which the temperature of the recording medium that has reached the colorimetric measurement unit decreases to 45 ° C or lower. Therefore, in the present invention, the temperature of the recording medium is lowered sufficiently by stopping the recording medium in the output path, transporting the recording medium at a low speed, or switching the transport path. If the temperature of the printing medium can be sufficiently lowered, the phenomenon of thermochromism is eliminated. As a result, it is possible to provide an image forming apparatus capable of achieving high-precision color matching and color stability.

[0047] First Embodiment

Imaging device

In the present embodiment, a method for resolving a previous problem will be described using an electrophotographic laser printer. In this case, an electrophotographic system is used as an example of an imaging system. However, the present invention can also be applied to an inkjet printer and a sublimation printer. The reason is that the present invention is effective in imaging devices in which a thermochromism phenomenon may occur in which the color of the measurement target changes due to temperature. Note that in the inkjet printer, an image forming unit is used to form an image on a printing medium by ink discharge and a fixing unit (drying unit) for drying the ink.

[0048] FIG. 1 is a cross-sectional graphical view showing a configuration of an image forming apparatus 100. The imaging apparatus 100 has a housing 101. In the housing 101, mechanisms are provided that make up a machine part and a part 104 comprising a control panel. Part 104 comprising a control panel includes a machine control part 102 for performing control associated with printing processes (e.g., a paper feed process) performed by appropriate mechanisms, and a printer controller 103.

[0049] As shown in FIG. 1, in a machine part, four stations 120, 121, 122 and 123 are provided associated with the YMCK (yellow-magenta-cyan-black), respectively. Stations 120, 121, 122 and 123 are image forming units for transferring toner to a print medium and forming an image. In this case, YMCK is an abbreviation for yellow, magenta, cyan and black. Each station consists essentially of conventional components. The photosensitive drum 105 is a kind of image carrier and is charged by the primary charger 111 to a uniform surface potential. A latent image is formed on the photosensitive drum 105 by means of laser radiation outputted by the laser 108. The developing device 112 develops a latent image using a dye (toner) and forms a toner image. The toner image (visible image) is initially transferred to the intermediate transfer element 106. A visible image formed on the intermediate transfer element 106 is secondly transferred to the transfer roller 114 relative to the printing medium 110 transported from the container 113.

[0050] The fixing process mechanism in the present embodiment consists of a first fixing device 150 and a second fixing device 160 for heating and pressing the toner image transferred to the recording medium 110 for fixing the toner image on the printing medium 110. The first fixing device 150 includes a fixing a roller 151 for applying heat to the printing medium 110, a pressure belt 152 for pressing the printing medium 110 to bring it into contact with the fixing roller 151 and the first post-f sensor 153 ksatsii for detecting the completion of locking. These rollers are hollow rollers and have a heater inside them. The rollers are driven by an engine, which is shown in the drawing, and transport the recording medium 110. The second fixing device 160 is located after the first fixing device 150 in the direction of transportation of the printing medium 110. The second fixing device 160 adds gloss and retains the fixation of the toner image on the printing medium 110 locked by the first locking device 150. Like the first locking device 150, the second locking device 160 also has iksiruyuschy roller 161, presser roller 162 and the second sensor 163 post-fixation. Some types of printing media 110 do not have to pass through the second fixing device 160. In this case, in order to reduce power consumption, the printing medium 110 passes through the transport route 130 without passing through the second fixing device 160. For example, if the installation for adding more gloss to the image on the print medium 110, or in the case where fixing requires a large amount of heat, for example, if the print medium 110 is thick paper, then the print medium 110, which passed through the first fixing device 150 is also transported to the second fixing device 160. In this case, if the recording medium 110 is plain paper or thin paper or the setting is not made to add more gloss, the recording medium 110 is transported to the transport route 130, which bypasses the second fixing device 160. An option of transporting the printing medium 110 to the second fixing device 160 or transporting the printing medium 110 bypassing the second fix the actuating device 160 is controlled by switching by the switching element 131.

[0051] The switching element 132 switches between the direction of the printing medium 110 to the output path 135 and the direction to the outward path 139. In release route 135, a circulation sensor 137 is provided. The front end of the recording medium 110 passes through the circulation sensor 137 and is transported to the circulation portion 136. After the sensor 137 detects the reversal of the rear end of the print medium 110, the conveying direction of the print medium 110 is switched. The switching element 133 switches between the direction of the print medium 110 to the transport path 138 to form a two-sided image and the direction to the release path 135. The switching element 134 directs the print medium 110 to the outward path 139.

[0052] After the second fixing device 160, in the transport direction of the recording medium 110, a color sensor 200 is arranged for detecting a measurement image (hereinafter referred to as an insertion image) on the recording medium 110. Four color sensors 200 may be arranged side by side in a direction perpendicular to the transport direction of the print medium 110, and are capable of detecting four rows of image inserts. Thus, a plurality of color sensors 200 can be provided. After issuing instructions for detecting color by the operation part 180, the machine control part 102 performs optical density adjustment, tone adjustment, multi-color adjustment, and the like.

[0053] An optical density sensor 170, which serves as an optical density detection unit, is provided opposite the intermediate transfer member 106. The optical density sensor 170 is a mirror reflection sensor provided with a light emitting element 171 consisting of a light emitting diode (LED) and a light receiving element 172. Although a mirror type sensor is used in the present embodiment, the sensor is not limited to this and, alternatively, may be a sensor of the type of diffuse reflection or a sensor in which both the mirror type of reflection and the diffuse type of reflection are used.

[0054] Color Sensor

2 is a graphical representation depicting the structure of a color sensor 200. Inside the color sensor 200, a white light LED 201, a diffraction grating 202, a linear sensor 203, a computing part 204 and a memory 205 are provided. The white light LED 201 is a light emitting element for irradiating the light of the image insert 220 on the recording medium 110. The diffraction grating 202 is a spectral component for dividing the light reflected by the insert image 220 along the wavelength. Linear sensor 203 is a light detection element including n light receiving elements for detecting light separated by a wavelength diffraction grating 202. Computing part 204 performs various types of calculations, starting with the light intensity value of each pixel detected by linear sensor 203. Various data used for computing part 204 is stored in memory 205. In computing part 204, for example, there is a spectrum calculation part for performing spectrum calculation from a light intensity value, a Lab calculation part for calculating a Lab value, and the like. A lens 206 may further be provided to collect the light emitted from the white light LED 201 in the insert image 220 on the recording medium 110 and collect the light reflected by the insert image 220 on the diffraction grating 202.

[0055] Profile

The image forming apparatus 100 creates a profile from the result of detecting insert images and converts the input image using this profile to form the output image. In this document, an ICC profile that has been recently adopted in the market is used as a profile that achieves excellent color reproducibility. However, the present invention is not an invention that can be applied solely to the ICC profile. The present invention can also be applied to a CRD (color rendering dictionary) proposed by Adobe, which has been progressively used in the PostScript level 2 language, in a color separation table in Photoshop, CMYK modeling in EFI's ColorWise to maintain black print information, etc. P.

[0056] The user operates the operating part 180 and issues a processing instruction for creating a color profile when the components are replaced by the installer before work, which requires accurate color matching if the user wants to know the colors of the final output during development or in similar cases.

[0057] The profile creation processing is performed by the printer controller 103 shown in the flowchart of FIG. 3. The printer controller 103, in which there is a central processor, reads a program for executing the flowchart described below from the storage part 350 and executes the program. Note that in FIG. 3, the contents of the printer controller 103 is composed of blocks to facilitate understanding of the processing performed by the printer controller 103. After the adoption of the profile creation instruction by the operation part 180, the profile creation part 301 outputs the CMYK color table, which is the test form ISO12642, to the machine control part 102 without a profile. The profile creating part 301 transmits a colorimetric measurement instruction to the color sensor control part 302. The machine control part 102 controls the image forming apparatus 100 and causes the image forming apparatus 100 to execute processes such as charging, exhibiting, developing, transferring and fixing. Thus, an ISO12642 test form is formed on the printing medium 110. The color sensor control part 302 controls the color sensor 200 in order to cause the color sensor 200 to measure the colorimetric value of the ISO12642 test form. The color sensor 200 outputs spectral reflection coefficient data that are the result of measuring a colorimetric value to a Lab calculation part 303 in the printer controller 103. Lab calculation part 303 converts the spectral reflection coefficient data into L * a * b * data and outputs the L * a * b * data to the color sensor input ICC profile storage part 304. The color sensor input profile ICC profile storage part 304 converts L * a * b * data inputted from the Lab calculation part 303 according to the color sensor input ICC profile, and outputs the converted L * a * b * data to the profile creation part 301. Note that Lab calculation part 303 can convert the spectral reflection coefficient data into a CIE1931XYZ color system, which is a color space signal that is machine independent (hardware). The color sensor input ICC profile stored in the color sensor input ICC profile storage portion 304 is comprised of a plurality of LUTs (lookup tables). These LUTs are, for example, a one-dimensional LUT for controlling the gamut of the input signal, a multi-color LUT called direct mapping, and a one-dimensional LUT for controlling the gamut of the generated transform data.

[0058] The profile creating part 301 creates an ICC output profile based on the relationship between outputting the CMYK color signal to the machine control part 102 and inputting L * a * b * data through the Lab calculation part 303. In the profile creating part 301, the generated ICC output profile is stored in place of the ICC output profile stored in the ICC output profile storage part 305.

[0059] The ISO12642 test form contains a small CMYK color correction adjustment insert that covers a color reproduction area that can be output using conventional copying techniques. Accordingly, the profile creating part 301 creates a color conversion table based on the relationship between the color signal values and the L * a * b * values obtained by measuring the colorimetric values. This creates a CMYK to Lab conversion table. An inverse transformation table is created based on this transformation table.

[0060] FIG. 4 depicts an ICC profile data configuration. An ICC profile includes a title, tags, and their data. Tags include color conversion table tags, white dot (wtpt), tag (gamt) to describe whether the color represented by the Lab value specified in the profile is within or outside the playback range, and the like.

[0061] The profile creation part 301, after receiving the profile creation command from the host computer via I / F 308 (interface), outputs the generated ICC output profile via I / F 308 to the host computer. The host computer can perform color conversion corresponding to the ICC profile using an application program.

[0062] Color Conversion Processing

When converting colors to output normal colors, the input of the image signal based on the assumption of the RGB signal input from the scanner part via I / F 308, or the standard value of the print CMYK signal, such as JapanColor, is transferred to the ICC input profile storage part 307 for external input. The ICC input profile storage part 307 performs RGB to L * a * b * or CMYK conversion to L * a * b * in accordance with the input of the image signal from I / F 308. The ICC input profile stored in the ICC input profile storage part 307, consists of many LUTs (lookup tables). These LUTs are, for example, one-dimensional LUTs for controlling the gamut of the input signal, a multi-color LUT called direct mapping, and a one-dimensional LUT for controlling the gamut of the generated transform data. The input image signal is converted from a device-specific color space to L * a * b * data that is device-independent using these LUTs.

[0063] The image signal converted to the chromaticity coordinates L * a * b * is input to CMM 306. “CMM” is an abbreviation for the color management module. CMM 306 performs various types of color conversion. For example, the CMM 306 performs a GUMAT transform to display a mismatch between the read color space, such as the part of the scanner serving as the input device, and the reproducible output color range of the image forming apparatus 100 serving as the output device. The CMM 306 also performs color conversion to control the mismatch between the type of light source in the input time period and the type of light source used when output is observed (also called color temperature mismatch). Thus, the CMM 306 converts the data L * a * b * into the data L '* a' * b '* and outputs the data L' * a '* b' * to the ICC output profile storage part 305. The profile created by measuring the colorimetric value is stored in the ICC output profile storage part 305. Accordingly, the output ICC profile storage part 305 performs color conversion on the data L '* a' * b '* based on the newly created ICC profile to convert them to a CMYK signal, which depends on the output device, and outputs the converted CMYK signal to the control part 102 by car.

[0064] In FIG. 3, the CMM 306 is separated from the ICC input profile storage part 307 and the ICC output profile storage part 305. However, as shown in FIG. 5, CMM 306 refers to a module that controls color management and color conversion using an input profile (print ICC profile 501) and an output profile (printer ICC profile 502).

[0065] control flow

The control of transporting the recording medium and measuring the colorimetric value, which is a feature of the present embodiment, will be described using the flowchart of FIG. 6 and an explanatory graphical representation of the position of the recording medium of FIG. 7.

[0066] In step S601, the printer controller 103 receives print medium information indicating the type of print medium (thickness, grammar (bulk), surface character, etc.) through the operation portion 180. If a sensor for detecting type is provided in the conveyance route of print media, the printer controller 103 may obtain print media information from this sensor.

[0067] In step S602, the printer controller 103 starts the color adjustment mode to perform color adjustment. A start instruction for this may also be adopted by the operation part 180.

[0068] In step S603, the printer controller 103 outputs the instruction of the machine control part 102 to supply the print medium 110. The machine control part 102 activates the conveyor roller drive motor 311 and supplies the print medium 110 from the container 113 to the conveyance path.

[0069] In step S604, the printer controller 103 instructs the machine control part 102 to control each station and causes the intermediate transfer member 106 to transfer the test form. The printer controller 103 also transmits print medium information to the machine control portion 102. The machine control part 102 secondarily transfers the test form from the intermediate transfer member 106 to the recording medium 110 using the transfer condition according to the type of recording medium based on the information of the recording medium.

[0070] In step S605, as a result of the printer controller 103 transmitting the print medium information to the machine control part 102, the machine control part 102 controls the first fixing device 150 and the second fixing device 160 using the fixing condition according to the type of printing medium and fixes the test form on the print medium 110. The machine control part 102 controls the switching element drive motor 312 to drive the switching element 131 in accordance with the type of printing medium for I am to cause the passage of the printing medium 110 exclusively through the first locking device 150, or both through the first locking device 150 and the second locking device 160. For example, the machine control part 102 causes the passage of the printing medium 110 exclusively through the first fixing device 150 to case of plain paper and causes the passage of the printing medium not only through the first fixing device 150, but also through the second fixing device 160 in the case of thick paper or coated paper mages.

[0071] In step S606, after the detection through the machine control part 102 that the front end of the recording medium 110 has passed through the first post-fix sensor 153 or the second post-fix sensor 163, the printer controller 103 causes a time period to be measured by the timer 310 in the part 102 machine controls. Here, in the present embodiment, the period of time necessary to lower the temperature of the recording medium 110 to the temperature of the medium is called the prescribed time period T. For example, the prescribed time period T is the time period when the color difference ΔE76 becomes less than 1.5 after the start of the count by the timer 310. In the present embodiment, taking into account the individual difference of the color sensor 200 and the read reproducibility of the correction insert of the same color, the measurement accuracy value of the target colorimetric value for the color sensor 200 is set as ΔE76 = 1.5.

[0072] Empirically, it was found that the change in the color of magenta due to temperature is greater than other colors. In particular, due to the relationship between the transportation time period, the temperature of the recording medium and the color difference ΔE of the magenta, in the present embodiment, the prescribed time period T is set to approximately 45 seconds. 7A-7C are graphical representations of locations at which the print medium 110 is waited for a prescribed time period T in the image forming apparatus 100.

[0073] In step S607, the printer controller 103 causes the transport of the print medium 110 to continue by the machine control part 102, and as a result, the front end of the print medium 110 passes through the color sensor 200, as shown in FIG. 7A. Note that at this stage, the controller 103 of the printer does not start measuring the colorimetric value.

[0074] In step S608, the printer controller 103 causes the transportation of the printing medium 110 to be continued further by the machine control part 102. After the sensor 137 detects that the recording medium 110 has reached the reversing portion 136, as shown in FIG. 7B, the printer controller 103 stops transporting the recording medium 110 by the machine control portion 102. Thus, the machine control part 102 stops the transport roller from driving by the drive motor 311. Thus, the print medium 110 waits in the access portion 136.

[0075] In step S609, the printer controller 103 determines whether a cooling period is necessary for the type indicated by the print medium information. For example, a table is stored in the printer controller 103 indicating whether a cooling time period is needed for each piece of print medium information. This table is stored, for example, in storage portion 350. The controller 103 of the printer determines whether a period of cooling time is required for each particular type with reference to the table. The determination of the need for a cooling time period is essentially the same as the determination of whether it is necessary to wait for the recording medium 110 in the handling part 136, and determining whether it is really necessary to reduce the transport speed of the printing medium 110 in the handling part 136. Accordingly, this table is an example of a table in which various sets of information of the printed medium are associated with the respective transportation routes (whether the direction to circulation part 136 is necessary) or transportation speeds (whether it is necessary to wait for the printed medium in the circulation part 136). As described above, the printer controller 103 obtains, from the table, the transport route or transport speed corresponding to the information of the print medium received by the operation part 180, and uses the obtained transport route or transport speed. If a cooling time period is required, the processing proceeds to step S610. If there is no need for a cooling time period, the processing skips steps S610 through S612 and proceeds to step S613.

[0076] In step S610, the printer controller 103 obtains a timer value from the timer 310 and determines whether the timer value exceeds the prescribed time period T. If the timer value exceeds the prescribed time period T, then the processing proceeds to step S611.

[0077] In step S611, the printer controller 103 causes the timer 310 to be reset by the machine control part 102.

[0078] In step S612, the printer controller 103 causes the transportation of the printing medium 110 to resume using the machine control part 102. The machine control part 102 resumes the movement of the conveyance roller drive motor 311, thereby causing the printing medium 110 to move in the direction of the color sensor 200.

[0079] In step S613, the printer controller 103 causes the transport of the print medium 110 to continue by the machine control part 102, and as a result, the print medium 110 passes through the color sensor 200, as shown in FIG. 7C.

[0080] According to the present embodiment, the prescribed time period T expires at that point in the time period when the recording medium 110 reaches the color sensor 200. Accordingly, the accuracy of measuring the colorimetric value dependent on the phenomenon of thermochromism at this moment is ΔE76 = 0.5 or less. For clarification, at this moment, a period of time has elapsed that is longer than the prescribed time period T. The reason is that the time period taken for the print medium 110 to reach the color sensor 200 proceeded further, since the transport of the print medium 110 was resumed in step S612. This time period is several seconds and does not adversely affect the measurement accuracy of the colorimetric value.

[0081] In step S614, the printer controller 103 causes the sensor 200 to measure the colorimetric value using the color sensor control portion 302. After the recording medium 110 has been colorimetric measured by the color sensor 200, it moves along the output path 139 and is discharged from the image forming apparatus 100, as shown in FIG. 7C.

[0082] Description of the effect

As described above, in accordance with the present embodiment, it is possible to lower the temperature of the recording medium 110 to a temperature suitable for measuring a colorimetric value by waiting the recording medium 110 for a prescribed period of time according to the type of recording medium 110.

[0083] Fig. 8 depicts the relationship of a sequence of time intervals between a timeout period, temperature, and ΔE76 (comparison based on 15 ° C) of the recording medium 110 and the position of the recording medium 110 in the conveying route. According to Fig. 8, the temperature of the recording medium 110 is about 65 ° C at a point (S607) when the recording medium 110 passes through the color sensor 200, immediately after the toner image is fixed on the recording medium 110. If the measurement of the colorimetric value is performed at this moment then a color difference of ΔE76 of approximately 2.4 occurs with respect to colors in a medium with a normal temperature (15 ~ 30 ° C) in which the user uses the final product. This means that the color difference ΔE76 exceeds the color stability standard [4.2.3] (where ΔE of each insert is 1.5 or less).

[0084] In the present embodiment, the printing medium 110 waits for the circulation part 136 for the prescribed time period T, and then it is transported again to the color sensor 200, and a colorimetric value is measured. The temperature of the recording medium 110 during this period of time is approximately 45 ° C or lower. Accordingly, in the present embodiment, it is possible to reduce the color difference ΔE76 to a level of less than 1.5 relative to the measurement result of the colorimetric value at a temperature of 15 ° C, which is implied as the lowest temperature in the environment where the image forming apparatus 100 is installed.

[0085] Fig. 9 depicts a possible temperature range of the print medium 110 in the image forming apparatus 100 depending on the type of print medium 110. In Fig. 9, the shading range 901 indicates the environment in which the operations of the image forming apparatus 100 are guaranteed. In the image forming apparatus 100 of the present embodiment, the temperature of the recording medium 110 immediately after fixing the insert image on the recording medium 110 is from 30 ° C to 70 ° C. Therefore, it should be understood that if it is desired to set the color difference ΔE76 based on the lowest temperature (15 ° C) in the installation environment to 0.5 or less, the prescribed time period T should be set uniformly to 45 seconds, regardless of the type of print medium 110.

[0086] In the present embodiment, the necessity or absence of the need for waiting is estimated according to the type of printing medium 110, and the prescribed time period T is determined according to the type of printing medium 110. In particular, the time period adopted for the measurement sequence of the colorimetric value may be minimized by dynamically adjusting the prescribed time period T in accordance with the type of recording medium 110.

[0087] The heat capacity of the print medium varies depending on its bulk or on the fact of the presence of surface coating material. With different heat capacities, the cooling time period (prescribed time period T) for cooling the recording medium 110 to the target temperature also varies.

[0088] FIG. 10 is a table showing the relationship between a prescribed time period T, which is a cooling time period, and types of printing medium 110. Referring to FIG. 10, three types of surface character are provided as examples, namely, plain paper paper coated on one side and paper coated on both sides. In relation to the main mass, three types are specified, namely, 60 g / m ² -109 g / m ² , 110 g / m ² -209 g / m ² and 210 g / m ² -350 g / m ² . In particular, the prescribed time period T can be set to 0 exclusively for plain paper (tissue paper) without a surface coating layer. Furthermore, by using the table shown in FIG. 10, the printer controller 103 can set the prescribed time period T to a minimum period of time in accordance with the type of printing medium 110. Thus, it is possible to shorten the time period for the entire measurement sequence of the colorimetric value by dynamic control prescribed period of time T. In this case, the table is stored in advance in the storage part 350.

[0089] As described above, in accordance with the present embodiment, the period of time from the moment when the recording medium 110 passes through the fixing unit to the moment when the colorimetric value measurement is performed by the color sensor 200 in the case where the colorimetric value measurement is performed by the color sensor 200, is set so that it is longer than the period of time taken to transport the print medium 110 from the fixing unit to the color sensor 200 in the case where measured e colorimetric values are not performed by the color sensor 200, and consequently colorimetric measurement values is performed in a state where the temperature of the print medium 110 is lowered sufficiently. Accordingly, even with a different thickness, bulk, or (different) surface character of the recording medium 110, the measurement result of the colorimetric value by the color sensor 200 can be stabilized. As a result, it is possible to achieve ΔE76 <1.5.

[0090] Second Embodiment

A feature of the present embodiment is that the colorimetric value is measured by the color sensor 200 after the prescribed time period T without using the timer 310 in the machine control portion 102 of the image forming apparatus 100. In particular, the present embodiment will be effective in imaging devices in which there is no standby position in which the stand is held by the print medium 110.

[0091] Imaging Device

Hereinafter, the configuration of the image forming apparatus according to the present embodiment will be described. 11A depicts an example in which the intermediate storage portion (buffer) 141 is provided in the image forming apparatus 100, and FIG. 11B depicts an example in which the intermediate storage portion 141 is provided outside the image forming apparatus 100.

[0092] In FIG. 11A, the intermediate storage part 141 is located on the side after the handling part 136 in the conveying direction of the print medium 110. The machine control part 102 switches between using and not using the intermediate storage part 141 by the switching member 1101. The transport speed in of the intermediate storage part 141 is set so as to be lower than the transportation speed in the transportation routes other than the intermediate storage part 141 la, to the printing medium 110 reaches the color sensor 200 after decreasing the temperature of the print medium 110 to a sufficient extent. Note that, instead of the conveyance speed, the conveyance length in the intermediate storage part 141 may be configured to be long enough to reduce the temperature of the recording medium 110 sufficiently.

[0093] In FIG. 11B, the intermediate storage unit 140 is attached on the side located after the image forming apparatus 100. The machine control part 102 switches between using and not using the intermediate storage part 141 by the switching element 1102. The transportation speed in the intermediate storage part 141 is set so as to be lower than the transportation speed in the transportation routes, except for the intermediate storage part 141, in order to so that the print medium 110 reaches the color sensor 200 after the temperature of the print medium 110 has decreased sufficiently. The post-processing unit 190, or the like, can be attached after the intermediate storage unit 140 in the direction of conveying the print medium 110. The post-processing unit 190 is a unit for executing the hole punching process, the weaving process, the stitching process, and the like. Such an intermediate storage unit 140 has such an advantage that it can be added to existing imaging devices.

[0094] The exhaust route that does not pass through the intermediate storage part 141 is the first transportation route to which the print medium 110 is directed when the measurement of the colorimetric value by the colorimetric value measuring unit is not performed. The exhaust path that passes through the intermediate storage part 141 is the second transport route to which the print medium 110 is directed when a colorimetric value is measured by the colorimetric value measuring unit. 11A and 11B, the transportation distance of the second transportation route is longer than the transportation distance of the first transportation route. In the case when the measurement of the colorimetric value is not performed, the controller 103 of the printer controls the conveyor roller, which is the conveyor unit, for transporting the printing medium 110 with a first conveyance speed. In the case where the measurement of the colorimetric value is performed, the controller 103 of the printer controls the transport roller so as to temporarily stop the print medium or transfer the print medium with a second transport speed that is slower than the first transport speed. The case of a temporary stop of the printing medium is an example of reducing the second conveying speed to zero, and its ideal solution from a technical point of view is common with the case of the first embodiment.

[0095] Note that in FIG. 11A, the front and back sides of the recording medium 110 are reversed after it has passed through the intermediate storage portion 141, and therefore, it is necessary to position the color sensor 200 from a side opposite to that of the sensor in FIG. 1. Further, in order to measure the colorimetric value of the recording medium 110, which should not pass through the intermediate storage part 141, it is necessary to arrange another color sensor 200 in the same position as in FIG. Thus, two color sensors 200 are needed. Of course, one color sensor 200 can also be used if the machine control part 102 performs transportation control so that the printing medium 110, which should not pass through the intermediate storage part 141, also passes through the intermediate storage part 141.

[0096] As described above, in the case where the intermediate storage part 141 cannot be installed in the housing 101 due to the dimensions of the housing of the image forming apparatus 100, it would be useful to use the intermediate storage unit 140 shown in FIG. 11B. Note that since the moment of performing the measurement of the colorimetric value after the expiration of the stipulated time period T is common for FIGS. 11A and 11B, basically, the measurement sequence of the colorimetric value is also common.

[0097] In the flowchart of FIG. 12, steps similar to the steps in the flowchart of FIG. 6 are assigned the same reference numerals and their description will be omitted. 12, after steps S601-S605 are completed, the processing proceeds to step S1201. In step S1201, the printer controller 103 drives the switching element drive motor 313 by the machine control part 102 in order to switch the transport route by the switching element 132, and directs the recording medium 110 to the output path 135.

[0098] In step S1202, the printer controller 103 determines whether a cooling period is necessary for the type indicated by the information of the print medium. The method for this determination is similar to the method performed in step S610. For example, the printer controller 103 determines whether a cooling time period is needed with reference to a table that is stored in the storage part 350. Determining whether a cooling period is necessary for a given type is essentially the same as determining whether a direction to the part is necessary 141 of the intermediate storage, and determining whether the transport speed of the recording medium in the intermediate storage portion 141 should be reduced. Accordingly, this table is an example of a table in which various sets of information of the print medium are associated with the respective transport routes (whether direction to the intermediate storage part 141 is necessary) or transport speeds (should the transport speed of the print medium in the intermediate storage part 141 be reduced). As described above, the printer controller 103 obtains, from the table, the transport route or transport speed corresponding to the information of the print medium received by the operation part 180, and uses the obtained transport route or transport speed. If a cooling time period is required, the processing proceeds to step S1203. If a cooling time period is not necessary, the processing proceeds to step S1204, and the printer controller 103 transfers the recording medium 110 to the color sensor 200.

[0099] In step S1203, the printer controller 103 induces the switching element 1101 to switch the transport path using the machine control part 102, and directs the recording medium 110 to the intermediate storage part 141. In addition, the printer controller 103 activates, using the machine control part 102, a conveyor roller drive motor 311 to drive the conveyor roller located in the intermediate storage part 141, and conveys the recording medium 110 along the conveyance path in the intermediate drive part 141. Note that the machine control part 102 drives the conveyance roller drive motor 311 so that the conveyance speed of the recording medium 110 in the intermediate storage part 141 is slower than the conveyance speed on other conveyance routes, such as exhaust route 135. Thus, the prescribed time period T is expended, and the temperature of the recording medium 110 can be sufficiently lowered. Note that in the image forming apparatus, in which a sufficient length of the transportation route in the intermediate storage part 141 can be provided, the transportation speed should not be reduced.

[0100] In step S1204, the printer controller 103 transports the print medium 110, which returns to the output path 135, then to the color sensor 200. After this, the processing proceeds to step S614, and a colorimetric value is measured.

[0101] Description of the effect

13 is a diagram showing, in a sequence of time intervals, a waiting period of a recording medium, a temperature of the recording medium, ΔE76 (comparison is based on 15 ° C) and the position of the recording medium (conveying distance). At the time when the rear end of the printing medium 110 passes through the switching element 1101, the machine control part 102 slows down the conveyance speed in the intermediate storage part 141 (S1203). Thus, the recording medium 110 passes through the color sensor 200 after the prescribed time period T has elapsed after the recording medium 110 leaves the fixing device.

[0102] In the second embodiment, like the first embodiment, the temperature of the print medium 110 is approximately 65 ° C at the time when the print medium 110 first passes through the color sensor 200. If a colorimetric value is measured at this point, a color difference of ΔE76 of approximately 1.7 occurs with respect to colors in a normal temperature environment (25 ° C) in which the user uses the end product. This value exceeds the standard for color reproduction stability [4.2.3] (ΔE of each insert is 1.5 or less).

[0103] In this case, in the present embodiment, the printing medium 110 can achieve the color sensor 200 after the prescribed time period T has elapsed, that is, after the temperature of the printing medium 110 is lowered to 45 ° C or lower by directing the medium 110 to the intermediate part 141 drive. Accordingly, the color difference ΔE76 relative to colors at the expected lowest temperature (15 ° C) in the environment where the image forming apparatus 100 is installed can be reduced to 1.5.

[0104] Third Embodiment

Regulation of maximum optical density

14 is a block diagram showing a system configuration of an image forming apparatus 100. First, the printer controller 103 issues instructions to the machine control part 102 to output a test pattern used in adjusting the maximum optical density. During this period of time, an insertion image is formed to control the maximum optical density for YMCK colors on a print medium 110 with a charge potential, exposure intensity, and developer bias voltage, which are set in advance or set for the last adjustment of the maximum optical density. After that, the machine control part 102 issues an instruction to the color sensor control part 302 for measuring the colorimetric value of the insert image.

[0105] After the colorimetric value of the insert image is measured by the color sensor 200, the measurement result of the colorimetric value is transmitted as spectral reflection coefficient data to the optical density conversion part 324. The optical density conversion part 324 converts the spectral reflection coefficient data into optical density data in CMYK and transmits the converted optical density data to the maximum optical density correction part 320.

[0106] The maximum optical density correction part 320 calculates a correction amount for the charge potential, exposure intensity and development bias voltage so that the maximum optical density of the output image is the desired value, and transmits the calculated correction values to the machine control part 102. The machine control portion 102 uses the transmitted correction values for the charge potential, exposure intensity, and development bias voltage for subsequent image forming operations. Using the above operation, the maximum optical density of the output image is adjusted.

[0107] Adjust the tone

After the adjustment of the maximum optical density has been completed, the printer controller 103 gives instructions to the machine control part 102 to generate an image insert 16 tones on a print medium 110. Note that the image signals for an image insert 16 tones can be, for example, 00H, 10H, 20H, 30H, 40H, 50H, 60H, 70H, 80H, 90H, A0H, B0H, C0H, D0H, E0H and FFH.

[0108] At this time, an insertion image of 16 tones of YMCK colors is formed on the print medium 110 using the correction amount for the charge potential, exposure intensity, and developer bias voltage calculated to maximize the control of optical density. After the 16-tone insert image is formed on the recording medium 110, the machine control part 102 gives instructions to the color sensor control part 302 for measuring the colorimetric value of the insert image.

[0109] After the colorimetric value of the insert image is measured by the color sensor 200, the colorimetric value measurement result is transmitted as spectral reflection coefficient data to the optical density conversion part 324. The optical density conversion part 324 converts the spectral reflection coefficient data into optical density data via CMYK and transmits the converted optical density data to the optical density tone correction part 321. The optical density tone correction portion 321 calculates a correction amount for an exposure amount in order to obtain a desired tonality. Then, the LUT creation part 322 creates the LUTs of monochrome tones and transmits the LUTs of monochrome tones as a signal value for each of the CMYK colors to the LUT part 323.

[0110] Managing inserts between sheets

The above tone control is not performed during operation due to the fact that the control takes a period of time. Therefore, during operation, an insert image is formed during an interval of a period of time between images (between sheets) on the intermediate transfer member 106, a change in optical density in these insert images is measured, and control is performed to reduce the change in optical density.

[0111] In this insertion control between sheets, among the insertion images formed during this time period of the above tone control, the insertion image of a certain average optical density of the carrier tone (40H in the present embodiment) is formed on the intermediate transfer member 106, and the optical density of this insert image is detected by the optical density sensor 170. The optical density sensor 170 is actuated by the optical density sensor control part 328 based on the instructions from the machine control part 102. The output of the optical density sensor 170 is transmitted to the optical density conversion part 325.

[0112] The optical density conversion part 325 converts the output from the optical density sensor 170 into CMYK optical density data. The LUT correction part 326 corrects the LUT of the monochrome tones set for the LUT part 323 so that the optical density data is set for a target value T set for the target value storage part 327. The desired tone characteristics can be obtained in this way by controlling the imaging conditions.

[0113] Color characteristics in thermochromism

Next, thermochromism characteristics of each color will be described. In response to a change due to heating of the molecular structure that forms the coloring matter, such as toner or ink, the reflection and absorption characteristics of light and color also change. As a result of testing by experiment, it was found that the tendency of color change for different coloring substances varies, as shown in Fig. 15. The horizontal axis in this diagram indicates the temperature of the image-insert, and the vertical axis indicates the change in color ΔE relative to the reference colors at 15 ° C.

[0114] Note that ΔE can be expressed as the three-dimensional distance of the following equation between two points (L1, a1, b1) and (L2, a2, b2) in the color space L * a * b * defined by CIE.

$$\Delta E=\sqrt{{\left(L\mathrm{one}-L2\right)}^2+{\left(a\mathrm{one}-a2\right)}^2+{\left(b\mathrm{one}-b2\right)}^2}$$

[0115] In FIG. 15, C is 100% cyan, M is 100% magenta, Y is 100% yellow, K is 100% black, and W is pure white. As shown in this drawing, the color change of magenta is especially large. As the temperature of the insert image increases, the color change of the insert image also increases, and an error occurs in the created ICC profile.

[0116] As an index of color matching accuracy and color stability, the average ΔE is set to 4.0 in the color matching accuracy standard (IT8.7 / 4 (insert ISO12642: 1617) [4.2.2]) in accordance with ISO 12647- 7. In addition, reproducibility [4.2.3], which is the standard of stability, sets ΔE of each insert as ≤1.5. To fulfill these conditions, it is desirable that the detection accuracy of the color sensor 200 satisfy the condition ΔE≤1.0. As shown in FIG. 15, in order to achieve ΔE≤1.0 for all YMCK colors, it is necessary to release the heat of the insert image and reduce its temperature to 34 ° C or lower.

[0117] Relationship between temperature and optical density value

As described above, the color value (Lab value) varies with temperature. Moreover, as a result of research carried out by the present applicants, it was found that the optical density value, essentially, does not change even in the case of a change in temperature and has no correlation with temperature. This result is shown in FIG.

[0118] A phenomenon in which, in the event of a temperature change, the chromaticity value changes, but the optical density value does not change, can be explained on the basis of the region in which the spectral reflection coefficient changes, and the difference in the methods for calculating the chromaticity value and the optical density value. By way of example, this point will be described by considering magenta (M), which has a large change in color ΔE taking into account temperature changes.

[0119] FIG. 17 shows spectral reflection coefficient data at each temperature obtained by measuring the colorimetric value of the magenta color insert image using the color sensor 200. FIG. 17A is an entire wavelength region from 400 to 700 nm, FIG. 17B is an enlarged graph depicting a wavelength region from 550 to 650 nm, and FIG. 17C is an enlarged graph depicting a wavelength region from 500 to 580 nm.

[0120] As shown in FIG. 15, if the temperature of the insert image varies from 15 to 60 ° C, then the magenta color change ΔE is approximately 2.0, and this color change ΔE is due to the coefficient being changed spectral reflection. It is difficult to understand the change in the spectral reflection coefficient in FIG. 17A, but in FIG. 17B, which increases the wavelength region from 550 to 650 nm, it can be found that the spectral reflection coefficient changes due to a change in the temperature of the insert image. The reason is that Lab calculation part 303 calculates the color using the spectral reflection coefficient over the entire wavelength region, and therefore, the color value changes due to a change in the spectral reflection coefficient.

[0121] In this case, as shown in Fig. 16, even if the temperature of the insert image varies in the range from 15 to 60 ° C, the optical density is essentially unchanged. The reason is that the optical density conversion part 324 calculates the optical density using a spectral reflection coefficient over a specific wavelength region. In particular, with respect to cyan, magenta, and yellow, the optical density conversion part 324 converts spectral reflectance data into optical density data using the filter of FIG. 18A. In addition, with regard to black, the optical density conversion part 324 converts spectral reflectance data into optical density data with visual spectral characteristics, as shown in FIG. 18B.

[0122] It should be understood that there is almost no change in the spectral reflection coefficient in the wavelength region shown in FIG. 17C. The region of FIG. 17C is a region having sensitivity characteristics to the green region of the spectrum in the wavelength region denoted by the horizontal axis in FIG. 18A, and the optical density value of magenta is calculated using the sensitivity characteristics of the green region of the spectrum, which is formed by the color opposite to magenta . Accordingly, there is almost no change in the coefficient of spectral reflection, even despite changes in temperature in this region, and, therefore, the value of optical density, essentially, also does not change.

[0123] As described above, the color of the insert image changes due to a change in temperature, despite the fact that the optical density of the insert image does not essentially change due to a change in temperature. Therefore, in the present embodiment, the measurement of the colorimetric value is performed by the color sensor 200 during the multicolor correction time period (during the ICC profile creation time period) after the heat of the recording medium 110 heated by the fixing device is released. Moreover, during the time period for controlling the maximum optical density and tone control, the measurement of the colorimetric value is performed by the color sensor 200 without releasing the heat of the print medium 110.

[0124] Techniques for solving the problem of thermochromism

FIG. 19 is a flowchart depicting operation in the image forming apparatus 100. This flow chart is performed by the printer controller 103. First, in step S1901, the printer controller 103 determines whether an imaging request has been submitted by the operation part 180 and whether an imaging request has been submitted by the host computer via the I / F (interface) 308.

[0125] If no image forming request has been filed, then in step S1902, the printer controller 103 determines whether the instruction for performing multicolor correction has been issued by the operation part 180. If the instruction for performing multicolor correction has been submitted, then in step S1903, the adjustment is performed the maximum optical density, which will be described later in the text in FIG. 20, and in step S1904, tone adjustment is performed, which will be described later in the text in FIG. 21. After that, in step S1905, multi-color correction processing is performed, which will be described later in the text in FIG. If no instruction for multicolor correction has been given in step S1902, the processing returns to the aforementioned step S1901. Thus, the adjustment of the maximum optical density and the tone control are performed before performing the multi-color correction processing to accurately perform the multi-color correction processing.

[0126] If it is determined in step S1901 that there is an image forming request, then in step S1906, the printer controller 103 feeds the print medium 110 from the container 113 and generates a toner image on the print medium 110 in step S1907. Then, in step S1908, the controller 103 The printer determines if image formation is complete on all pages. If the image formation on all pages is completed, then the processing returns to step S1901, otherwise, the processing returns to step S1906, and the image formation on the next page is performed. Note that each time period when image formation is performed for a prescribed number of pages, the aforementioned insertion control between pages is performed to stabilize the optical density.

[0127] FIG. 20 is a flowchart depicting an operation for performing maximum optical density adjustment. This flow chart is performed by the printer controller 103. Note that the image forming apparatus 100 is controlled by the machine control part 102 in response to an instruction from the printer controller 103.

[0128] First, in step S2001, the printer controller 103 feeds the recording medium 110 from the container 113 and forms, on the recording medium 110, in step S2002, an insert image for adjusting the maximum optical density of the YMCK colors. Next, in step S2003, after the print medium 110 reaches the color sensor 200, the printer controller 103 measures the image insert by the color sensor 200.

[0129] Then, in step S2004, the printer controller 103 converts, using the optical density conversion part 324, spectral reflection coefficient data outputted by the color sensor 200 to CMYK optical density data. Thereafter, in step S2005, the printer controller 103 calculates correction values for the charge potential, exposure intensity, and development bias voltage based on the converted optical density data. The correction values calculated at this stage are stored for use in the storage part 350.

[0130] FIG. 21 is a flowchart depicting an operation for adjusting a tone. This flow chart is performed by the printer controller 103. Note that the image forming apparatus 100 is controlled by the machine control part 102 in response to an instruction from the printer controller 103.

[0131] First, in step S2101, the printer controller 103 feeds the recording medium 110 from the container 113. In step S2102, an insertion image (16 tones) is formed on the recording medium 110 to adjust the color tone of the YMCK. Then, after the print medium 110 reaches the color sensor 200, in step S2103, the printer controller 103 measures the image insert using the color sensor 200.

[0132] Then, in step S2104, the printer controller 103 converts, using the optical density conversion part 324, spectral reflection coefficient data outputted by the color sensor 200 to the optical density data by CMYK. After that, in step S2105, the printer controller 103 creates a LUT for tone correction based on the converted optical density data. The LUT calculated at this stage is set for use in part 323 of the LUT.

[0133] FIG. 22 is a flowchart depicting an operation for performing multicolor correction processing. This flow chart is performed by the printer controller 103. Note that the image forming apparatus 100 is controlled by the machine control part 102 in response to an instruction from the printer controller 103.

[0134] First, in step S2201, the printer controller 103 feeds the print medium 110 from the container 113. In step S2202, an insert image is formed on the print medium 110 for multicolor correction processing. Next, in step S2203, the printer controller 103 expects the print medium 110 to reach the print portion 136 based on the detection of the front end of the print medium 110 by the print sensor 137. In step S2204, after the print medium 110 reaches the handling part 136, the printer controller 103 controls the transport roller drive motor 311 in such a way as to stop the transport of the print medium 110.

[0135] After stopping the transportation of the recording medium 110 in step S2204, in step S2205, the printer controller 103 performs the calculation of the target value, which will be described later using FIG. 23. This target value calculation processing is a process for calculating the target value T used in the aforementioned insertion control between sheets. At this point, both maximum optical density control and tone control are performed, and therefore the optical density of the output image has already been adjusted to the desired optical density. Accordingly, at this moment, it is necessary to form an insert image on the intermediate transfer element 106 and set the optical density value of this insert image to the target value T when controlling the insert between sheets.

[0136] After the target value calculation processing is completed in step S2206, the printer controller 103 determines whether the prescribed period of time (40 seconds in the present embodiment) has elapsed after the transportation of the recording medium 110 has stopped in step S2204. Determining whether the prescribed period of time has elapsed is performed based on the counting value of the timer that starts after the transportation of the recording medium 110 is stopped. Thus, by stopping the transportation of the recording medium 110 for a prescribed period of time, the heat of the image insert on the recording medium 110 is released. , color variation due to the influence of thermochromism can be reduced.

[0137] Note that, as shown in FIG. 15, in order to achieve ΔE of all YMCK colors ≤1.0, it is necessary to release heat from the insert image and lower its temperature to 34 ° C or lower. In this case, in the present embodiment, the time period necessary for the release of heat is set to 40 seconds. By stopping the recording medium 110 for 40 seconds, heat can be released so that the temperature is lowered to 34 ° C or lower even if the first fixation heater 342 provided for the first fixation device 150 and the second fixation heater 343 provided for second locking device 160.

[0138] After the 40-second stop period has elapsed in step S2207, the printer controller 103 controls the conveyance roller drive motor 311 so as to resume transporting the recording medium 110. At this time, the printer controller 103 changes the conveying direction of the recording medium 110 and conveys the recording medium 110 to 200 color sensor.

[0139] After the print medium 110 reaches the color sensor 200 in step S2208, the printer controller 103 measures the image insertion by the color sensor 200. Then, the printer controller 103 calculates the color data (L * a * b *) using the Lab calculation part 303 from the spectral reflection coefficient data outputted by the color sensor 200. In step S2209, the printer controller 103 creates an ICC profile by the above processing based on the color data (L * a * b *). In step S2210, the ICC profile is stored in the ICC output profile storage part 305.

[0140] FIG. 23 is a flowchart depicting an operation for performing processing for calculating a target value. This flow chart is executed by the controller 103 of the printer. Note that the image forming apparatus 100 is controlled by the machine control part 102 in response to an instruction from the printer controller 103. The target value calculation processing, as shown in FIG. 22, is performed in the process of stopping the transportation of the recording medium 110 and releasing its heat.

[0141] First, in step S2301, the printer controller 103 generates an insert image for performing inter-sheet control on the intermediate transfer member 106. As mentioned above, the value of the image-insert signal generated at this stage is 40H. Then, in step S2302, the printer controller 103 measures the optical density of the insert image using the optical density sensor 170.

[0142] In step S2303, the printer controller 103 calculates the optical density of the insert image as the target value T used in managing inserts between sheets. In step S2304, the target value T is stored in the target value storage part 327. Thus, in this flowchart, the output from the optical density sensor 170 that detects the image insert is converted to YMCK optical density data, and this optical density data is stored as the target value T in the target value storage part 327.

[0143] Note that, when managing inserts between sheets, the printer controller 103 compares the measured value of the insert image formed on the intermediate transfer element 106 during subsequent operations with the target value T stored in the target value storage part 327 in step S2304 and corrects LUT.

[0144] Description of the effect

The color change due to the influence of thermochromism is reduced by performing the above control, and thus, it is possible to accurately detect the color of the image insert and improve performance. Fig. 24 shows a comparison of the total time period taken to perform all of the following actions, namely: adjusting the maximum optical density, adjusting the tone, processing the multicolor correction, and processing to calculate the target value, in the present embodiment and in the comparative example. Note that in the comparative example, the target value calculation processing is performed after the multi-color correction processing is completed.

[0145] In the calculation processing of the target value for inserting control between sheets, the image-insert of the image signal 40H was formed on the intermediate transfer element 106, and the optical density of this insert image was measured, which took approximately 30 seconds. Note that to further improve the accuracy, not only the target value T of the image-insertion of the image signal 40H, but also the target values of other image signals can be used to generate and measure the image-insertion, and in this case, the processing of calculating the target value takes more time than 30 seconds.

[0146] As is clear from FIG. 24, compared with the comparative example, the present embodiment is able to decrease to only 30 seconds, that is, 20% of the time period, by performing the calculation of the target value within the multi-color correction processing.

[0147] As described above, in the present embodiment, the target value calculation processing is performed during the multi-color correction processing after the printing medium 110 passes through the fixing device, until the colorimetric value is measured by the color sensor 200. In particular, in the present embodiment, the processing for calculating the target value used to control the inserts between the sheets is performed at a time when the transport of the printing medium 110 is stopped and the heat release of the image-insert is completed. Therefore, in the present embodiment, the color change due to the influence of thermochromism is reduced, and it is possible to accurately detect the color of the measurement image and improve performance.

[0148] Note that in the above description, the heat of the printing medium 110 is released by temporarily stopping the printing medium 110 after transporting the printing medium 110 through the fixing device, until the measurement of the colorimetric value is performed by the color sensor 200. Moreover, the measurement time of the colorimetric value can be delayed by reducing the transport speed of the print medium 110 instead of temporarily stopping the print medium 110.

[0149] Fourth Embodiment

Techniques for solving the problem of thermochromism

25 is a flowchart depicting operation in the image forming apparatus 100. This flow chart is performed by the printer controller 103. First, in step S2501, the printer controller 103 determines whether an imaging request has been submitted by the operation part 180 and whether an imaging request has been submitted by the host computer via I / F 308.

[0150] If no image forming request has been filed, then at step S2502, the printer controller 103 determines whether an instruction to perform multicolor correction has been issued by the operation part 180. In step S2503, if an instruction to perform multicolor correction has been submitted, processing is performed multicolor correction, which will be described later in Fig.26. If no instruction to perform multicolor correction has been filed, the processing returns to the aforementioned step S2501.

[0151] If it is determined in step S2501 that an image forming request has been submitted, then in step S2504, the printer controller 103 feeds the recording medium 110 from the container 113. In step S2505, a toner image is formed on the recording medium 110. Then, in step S2506, the printer controller 103 determines whether imaging on all pages is completed. If the image formation on all pages is completed, the processing returns to step S2501, otherwise, the processing returns to step S2504, and image formation is performed on the next page.

[0152] FIG. 26 is a flowchart depicting an operation for performing multicolor correction processing. This flow chart is performed by the printer controller 103. Note that the image forming apparatus 100 is controlled by the machine control part 102 in response to an instruction from the printer controller 103.

[0153] First, in step S2601, the printer controller 103 feeds the print medium 110 from the container 113. In step S2602, an insert image is formed on the print medium 110. Then, in step S2603, the printer controller 103 waits until a reference is detected by the access sensor 137 rear end of recording medium 110.

[0154] After detecting the rear end of the recording medium 110 by the access sensor 137 in step S2604, the printer controller 103 controls the conveyance roller drive motor 311 in such a way as to stop the transport of the recording medium 110. Then, in step S2605, the printer controller 103 waits for a period of time T after stopping the transportation of the printing medium 110. Thus, the heat of the image-insert on the printing medium 110 is released in the process of temporarily stopping the printing medium CITEL 110 in part 136 treatment. Thus, the color change due to the influence of thermochromism can be reduced. Note that the time period T is set in accordance with the settings of the bulk, surface character and gloss of the print medium 110. Next, this point will be described in detail.

[0155] After the stop time period T has elapsed in step S2606, the printer controller 103 controls the transport roller drive motor 311 so as to resume transport of the print medium 110. At this time, the printer controller 103 changes the transport direction of the print medium 110 and conveys the print medium 110 to the sensor 200 colors.

[0156] After the print medium 110 reaches the color sensor 200 in step S2607, the printer controller 103 measures the image insertion by the color sensor 200. Thereafter, in step S2608, the printer controller 103 creates an ICC profile using the above processing based on the result of the measurement of the colorimetric value performed by the color sensor 200. In step S2609, the ICC profile is stored in the storage section of the output ICC profile 305.

[0157] Setting a time period for heat release

The image forming apparatus 100 has seven fixation modes depicted in FIG. 28. The reason for such preparation of several modes is that it is necessary to change the fixation conditions in accordance with the settings of the bulk, the nature of the surface and gloss of the print medium 110.

[0158] FIG. 27 are diagrams illustrating print media setting screens. The screens shown in FIGS. 27A and 27B are displayed on a touch-sensitive display panel provided in the operating part 180. The user selects, from the screen in FIG. 27A, for which cartridge in the container 113 the user configures the settings. For example, after selecting the cartridge 1, the screen of FIG. 27B appears, and it is possible to adjust the bulk, surface nature and gloss of the print medium 110 contained in the cartridge 1.

[0159] The amount of heat required for fixing must be changed in accordance with the settings of the bulk, surface and gloss of the print medium 110. The reason is that the amount of heat absorbed by the print medium 110 when the toner image formed on the print media 110, heats and fixes, varies depending on the bulk of the printing medium 110. In addition, if a large amount of heat is applied to paper with a rough surface, such as recycled paper, then the toner penetrates deeply into the paper fiber and the quality deteriorates, and solving the problem of this phenomenon is another matter. In addition, in order to meet user requirements regarding the degree of gloss, it is necessary to prepare several fixing modes.

[0160] Fig. 29 depicts the setting of the fixing mode in the case where the recording medium 110 is recycled paper, Fig. 30 depicting the settings of the fixing mode in the case where the printing medium 110 is paper of excellent quality, and Fig. 31 depicting the setting of the fixing mode in case where the print medium 110 is coated paper. The machine control part 102 controls the first fixing heater 342 provided for the first fixing device 150 and the second fixing heater 343 provided for the second fixing device 160, in accordance with the bulk, surface character and gloss set by the operation part 180.

[0161] As shown in FIG. 30, for example, if the gloss of the recording medium 110, which is excellent quality paper, has a bulk of 80 g / m ² , changes from “standard” to “-1”, then the temperature of the first fixing device 150 ranges from 180 ° C to 165 ° C. In addition, for example, if a gloss of “+1” is selected for a recording medium that is excellent quality paper and has a bulk of 80 g / m ² , then the use of the second fixing device 160 is set to the same as the first fixing device 150 .

[0162] Thus, under different fixing conditions, the temperature of the recording medium 110 also differs during the period of time when the colorimetric value is measured by the color sensor 200. Accordingly, it is necessary to adjust the waiting period T used in the time period when the recording medium 110 is stopped in the circulation part 136 for releasing heat in step S2605 of FIG. 26, in accordance with the paper weight, surface character and gloss.

[0163] When determining the waiting period T for heat release, it is necessary to take into account (1) the distance from the fixing device through which the recording medium last passed to the circulation part 136, (2) the fixing temperature and (3) the heat release characteristics print medium 110.

[0164] (1) The distance from the second fixing device 160 to the reversing part 136 is shorter than the distance from the first fixing device 150 to the reversing part 136. Therefore, the time period for heat release until the printing material 110 reaches the circulation part 136, which passes through both the first fixing device 150 and the second fixing device 160, is shorter than the time period for the printing medium 110, which passes exclusively through the first fixing the device 150, and therefore the waiting period T in the access portion 136 for the previous print medium 110 is set to be longer.

[0165] (2) As the fixing temperature rises, the recording medium 110 retains more heat. Accordingly, as the fixation temperature rises, it is necessary to set a longer period T of the waiting time in the reference part 136.

[0166] (3) As the heat release characteristics of the printing medium 110 increase, heat from recycled paper, high quality paper, and coated paper is effectively released in the above order. In addition, as the bulk of the print medium 110 decreases, heat is released even more efficiently.

[0167] Subject to the above paragraphs (1) to (3), the present applicants received respective waiting periods T by experimenting using the image forming apparatus 100. Fig. 32 depicts waiting periods T in the circulation part 136 in the case where the recording medium 110 is recycled paper, Fig. 33 depicts the waiting times T in the circulation part 136 in the case when the printing medium 110 is high quality paper, and .34 depicts waiting periods T in the handling portion 136 in the case where the recording medium 110 is coated paper.

[0168] As shown in FIGS. 32-34, the timeout period T is changed in accordance with the settings of the bulk, surface and gloss of the recording medium 110, and the initial time period for measuring the colorimetric value by the color sensor 200 is changed. Thus, it is possible to release the heat of the image-insert and reduce its temperature to 34 ° C for a period of time from the start of measuring the colorimetric value by the color sensor 200, and achieve ΔE≤1.0.

[0169] As described above, in the present embodiment, a period of time from the moment when the recording medium 110 passes through the fixing device to the moment when the colorimetric value measurement is performed by the color sensor 200 is controlled based on the contents of the paper type settings for the recording medium 110 Thus, in the present embodiment, the color change due to the influence of thermochromism is reduced, and the color of the insert image can be accurately detected.

[0170] Note that in the present embodiment, the waiting time period T of the recording medium 110 in the access portion 136 is optimized, but the configuration is not limited to it provided that it is possible to adjust the time period from the moment when the recording medium 110 passes through the fixing device to the moment he reaches the 200 color sensor. For example, the speed of the recording medium 110 can be reduced, the period of time from the moment when the recording medium 110 passes through the fixing device to the moment when it reaches the color sensor 200 can be adjusted by controlling the time period of the deceleration.

[0171] Although the present invention has been described with reference to exemplary embodiments, it should be understood that the invention is not limited to the disclosed exemplary 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.

[0172] This application claims the priority of Japanese Patent Application No. 2011-194414 filed September 6, 2011, Japanese Patent Application No. 2011-226025 filed October 13, 2011, and Japanese Patent Application No. 2011-221233 October 5, 2011, which are hereby fully incorporated into this document.

Claims (15)

1. An image forming apparatus comprising:
an image forming unit configured to form an image on a print medium;
a fixing unit configured to fix an image on a print medium;
a transport unit configured to transport the print medium along the transport path and change the transport direction of the print medium that passes through the fixing unit to the opposite;
a color measuring unit configured to measure, after the fixing unit in the transport direction of the print medium, the color of the image recorded on the print medium; and
a control unit configured to control the transportation unit so that the period from the moment when the edge of the printing medium passes through the fixing unit to the moment when the said edge of the printing medium, the transport direction of which is reversed, passes through the measurement position of the color measuring unit in the case when the color measuring unit measures the color of the image recorded on the printing medium was longer than the time interval from the moment when the edge of the printing medium pro goes through the fixing unit, until the mentioned edge of the printing medium, the transport direction of which is reversed, passes through the measurement position of the color measuring unit in the case when the color measuring unit does not measure the color of the image fixed on the printing medium. 2. The image forming apparatus according to claim 1, wherein the fixing unit has a heater configured to heat an image to fix an image on a print medium. 3. The image forming apparatus according to claim 1, wherein the image forming unit is an ink supply and image forming unit, and
the fixing unit is a drying unit configured to dry ink. 4. The image forming apparatus according to claim 1, wherein in the case where the color measuring unit measures the color of the image recorded on the print medium, the control unit controls the transport unit for transporting the print medium after the control unit controls the transport unit to stop the print medium media for a predetermined period of time. 5. The image forming apparatus according to claim 4, wherein the predetermined time period is a period of time at which the color difference ΔE76 obtained by the color measuring unit based on the temperature in the environment where the image forming apparatus is installed is 1.5 or less. 6. The image forming apparatus according to claim 4, wherein the predetermined period of time is a period of time at which the temperature of the recording medium that has reached the color measuring unit decreases to 45 ° C or lower. 7. An image forming apparatus according to claim 4, further comprising:
a receiving unit, configured to accept input of information about the print medium that indicates the thickness, bulk, or surface of the print medium, and
however, many predetermined time intervals are set for the corresponding information about the print medium, and
wherein the control unit determines a predetermined period of time corresponding to information about the print medium received by the adoption unit. 8. The image forming apparatus according to claim 1, wherein the control unit controls, based on the type of print medium, the period of time from the moment when the edge of the print medium passes through the fixing unit until the moment when said edge of the print medium passes through the measurement position. 9. The image forming apparatus according to claim 1, wherein the control unit controls the transportation unit to reduce the transportation speed of the recording medium during the period from the moment when the recording medium passes through the fixing block to the moment when said recording medium reaches the measurement position. 10. The image forming apparatus according to claim 1, wherein the control unit controls, based on the fixing temperature used to fix the image on the printing medium by the fixing unit, the time interval from the moment when the edge of the printing medium passes through the fixing unit until the moment when said edge The print medium passes through the measurement position. 11. The image forming apparatus of claim 1, wherein
the transportation path includes a part of the reversal, and
the transportation unit changes the direction of transportation of the print medium by reverse switching the print medium in terms of changing the direction to the opposite. 12. An image forming apparatus according to claim 1, further comprising
a conversion unit configured to convert the image signal based on the conversion condition; and
an update unit configured to update said conversion condition based on an image measurement result by a color measurement unit,
wherein the image forming unit is further configured to generate an output image based on the image signal converted by the conversion unit. 13. The image forming apparatus according to claim 1, wherein the color measuring unit includes:
a radiation unit configured to radiate an image with light;
a diffraction grating configured to scatter light reflected by the image; and
a linear sensor configured to receive light scattered by a diffraction grating. 14. The image forming apparatus according to claim 13, wherein the color measuring unit is configured to measure the color of the image recorded on the print medium based on the light intensity received by the linear sensor, the wavelength of which is in the range between 400 nm and 700 nm. 15. The image forming apparatus according to claim 1, wherein the edge of the recording medium is the edge of the front end of the recording medium in the transport direction for a period of time for transporting the recording medium from the fixing unit to the measurement position of the color measuring unit.

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