Image forming apparatus and method for controlling image forming apparatus

Abstract

To provide an image forming apparatus capable of specifying a color value after color stabilization of an image formed in various use situations in a shorter time.SOLUTION: An image forming device 1 according to the present disclosure includes a control unit 40 that continuously performs color measurement of an image immediately after the image is formed by test printing, and specifies a color value after color stabilization of the image, and a storage unit 60 that stores a color measurement result and an image forming condition in association with each other as history-data D1 for test printing performed in the past. Then, when the control unit 40 performs new test printing and continuously performs color measurement of the image formed by the test printing, in a case where a difference in transition between the time-series color measurement date of the image formed by the new test printing obtained up to the present time and the time-series color measurement date of the color measurement result stored as the history date D1 is equal to or less than a predetermined value the control unit 40 determines that the color measurement is completed at that time.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure relates to an image forming apparatus and a control method for the image forming apparatus. [Background technology]

[0002] In general, inkjet image forming devices perform a process of performing test printing on a recording medium, measuring the color of the printed pattern with a colorimeter, and updating correction values ​​for density gradation correction and the like based on the obtained color values ​​(see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-131483 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the ink used in this type of image forming apparatus requires a certain amount of time for the color to stabilize after being ejected onto the recording medium. Therefore, particularly in industrial printing and the like, due to the demand for accurate color reproducibility, color measurement using a colorimeter is performed after image formation has been completed, waiting until the color has stabilized.

[0005] Figure 1 shows an example of the time progression of color change in an image formed on a recording medium. In Figure 1, the horizontal axis represents the time elapsed since immediately after image formation, and the vertical axis represents the color difference (i.e., the amount of change from the initial value) of the color value measured at each point in time.

[0006] Generally, the stabilization time required for ink to dry on a recording medium and stabilize its color varies depending on various factors, such as the type of recording medium, the type of ink, and the temperature and humidity during printing. For this reason, for example, Patent Document 1 describes a process in which color measurement is repeated periodically, and when the color change per unit elapsed time becomes small, the color is deemed to have stabilized, and final color measurement is performed.

[0007] However, in the conventional technology disclosed in Patent Document 1, the image forming apparatus actually had to wait until the ink on the recording medium dried and the color stabilized, which meant that printing could not be performed during that waiting time, resulting in downtime.

[0008] The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide an image forming apparatus and a control method thereof that enable the color values ​​of images formed under various usage conditions to be determined in a shorter time after color stabilization.

[0009] Here, "color value" refers to color information related to hue, lightness, and saturation. However, the "color value" may be expressed in any color coordinate system, such as the Lab color space or the RGB color space. [Means for solving the problem]

[0010] The main invention that solves the above-mentioned problems is: an image forming unit that forms an image on a recording medium by ejecting ink; a color measurement unit that performs color measurement of the image formed on the recording medium; a control unit that controls the operations of the image forming unit and the colorimetric unit, performs test printing, and continuously measures the color of the image immediately after the image is formed in the test printing, and identifies the color value of the image after color stabilization based on time-series colorimetric data; a storage unit that stores the color measurement results and image forming conditions of the test printing performed in the past as history data in association with each other; Equipped with The control unit When a new test print is performed and colorimetry of the image formed in the test print is continuously performed, Among the color measurement results stored as the history data, the color measurement results obtained under the image forming conditions that are the same as or similar to those of the new test print are referenced; If the difference in the transition between the time-series colorimetric data obtained up to the present time of the image formed by the new test print and the time-series colorimetric data of the referenced colorimetric result is equal to or less than a predetermined value, the colorimetric measurement is deemed to be completed at that point. An image forming apparatus.

[0011] In other respects, A control method for an image forming apparatus, which performs test printing and continuously measures the color of the image immediately after the image is formed on a recording medium in the test printing, and specifies color values ​​of the image after color stabilization based on time-series color measurement data, In a storage unit that associates colorimetry results with image forming conditions for the test printing that has been performed in the past and stores them as history data, the colorimetry results of the test printing that have been performed under image forming conditions that are the same as or similar to those of the new test printing are referenced from among the colorimetry results stored as the history data; If the difference in the transition between the time-series colorimetric data obtained up to the present time of the image formed by the new test print and the time-series colorimetric data of the referenced colorimetric result is equal to or less than a predetermined value, the colorimetric measurement is deemed to be completed at that point. It is a control method. [Effects of the Invention]

[0012] According to the image forming apparatus of the present invention, it is possible to specify, in a shorter time, the color values ​​of images formed under various usage conditions after color stabilization. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 10 is a diagram showing an example of the transition over time of color change in an image formed on a recording medium. [Figure 2] FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 3] FIG. 1 is a schematic diagram illustrating the configuration of a head unit according to an embodiment of the present invention. [Figure 4] FIG. 1 is a block diagram showing the configuration of a control system of an image forming apparatus according to an embodiment of the present invention. [Figure 5] FIG. 10 is a diagram showing an example of history data stored in a storage unit according to an embodiment of the present invention. [Figure 6] FIG. 10 is a diagram showing an example of an operation flow of a control unit according to an embodiment of the present invention. [Figure 7] FIG. 7 is a diagram illustrating the time-saving color measurement flow of steps S7 to S10 in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functions are designated by the same reference numerals, and redundant description will be omitted.

[0015] An example of the configuration of an image forming apparatus (hereinafter referred to as "image forming apparatus 1") according to one embodiment of the present invention will be described below with reference to Figures 2 to 4. Note that the image forming apparatus 1 is configured to perform test printing (see Figure 6, etc.) as a calibration process before performing actual printing in order to perform density gradation correction and the like suitable for image formation conditions.

[0016] FIG. 2 is a diagram showing a schematic configuration of the image forming apparatus 1. As shown in FIG.

[0017] The image forming apparatus 1 is an inkjet type image forming apparatus that forms an image by ejecting (spinning) ink from nozzles formed in a recording head 240 and causing it to land on a recording medium P such as paper.

[0018] The image forming apparatus 1 includes a paper feed section 10, an image forming section 20, a paper discharge section 30, a control section 40, and a color measurement section 50.

[0019] Under the control of the control unit 40, the image forming apparatus 1 transports the recording medium P stored in the paper feed unit 10 to the image forming unit 20, which ejects ink onto the recording medium P to record an image, and transports the recording medium P with the recorded image to the paper discharge unit 30. The image forming apparatus 1 is also configured so that the color measurement unit 50 can measure the color of the image formed in the image forming unit 20 as needed, such as during test printing.

[0020] More specifically, the image forming apparatus 1 records a color image on the recording medium P by overlapping four colors, yellow (Y), magenta (M), cyan (C), and black (K), at a predetermined number of recording gradations on the recording medium P. In the following description, the ink colors of yellow (Y), magenta (M), cyan (C), and black (K) will be abbreviated as Y, M, C, and K.

[0021] As the recording medium P, various media capable of fixing ink that has landed on the surface, such as plain paper or coated paper, fabric or sheet-like resin, can be used. Note that in this embodiment, a mode in which paper is used as the recording medium P is shown.

[0022] The paper feed unit 10 has a paper feed tray 11 that stores the recording medium P, and a medium supply unit 12 that transports and supplies the recording medium P from the paper feed tray 11 to the image forming unit 20. The medium supply unit 12 has a ring-shaped belt supported on the inside by two rollers, and transports the recording medium P from the paper feed tray 11 to the image forming unit 20 by rotating the rollers with the recording medium P placed on this belt.

[0023] The image forming section 20 includes a conveying section 21, a delivery unit 22, a heating section 23, a head unit 24, a fixing section 25, and a delivery section 26.

[0024] The conveying unit 21 holds the recording medium P placed on the conveying surface of a cylindrical conveying drum 211. The conveying drum 211 rotates around its rotation axis and moves around in an orbit, thereby conveying the recording medium P on the conveying drum 211 in a conveying direction along the conveying surface.

[0025] The conveying drum 211 has claws and an air intake section (not shown) for holding the recording medium P on its conveying surface. The recording medium P is held on the conveying surface by having its edges pressed down by the claws and being drawn to the conveying surface by the air intake section.

[0026] The delivery unit 22 is provided at a position between the medium supply unit 12 and the transport unit 21 of the paper feed unit 10. The delivery unit 22 holds and picks up one end of the recording medium P transported from the medium supply unit 12 with a swing arm unit 221, and delivers it to the transport unit 21 via a delivery drum 222.

[0027] The heating unit 23 is provided between the position where the delivery drum 222 is disposed and the position where the head unit 24 is disposed. The heating unit 23 heats the recording medium P conveyed by the conveyance unit 21 so that the temperature of the recording medium P falls within a predetermined temperature range. The heating unit 23 has, for example, an infrared heater or the like, and energizes the infrared heater based on a control signal supplied from the control unit 40 to cause the infrared heater to generate heat.

[0028] The head unit 24 records an image by ejecting ink onto the recording medium P at appropriate timing according to the rotation of the transport drum 211 on which the recording medium P is held.

[0029] The head units 24 are arranged such that their own ink ejection surfaces are spaced a predetermined distance from the transport surface of the transport drum 211. In the image forming apparatus 1 of this embodiment, four head units 24, each corresponding to one of the four colors of ink, Y, M, C, and K, are arranged at predetermined intervals from the upstream side in the transport direction of the recording medium P in the order of Y, M, C, and K.

[0030] The head unit 24 is used in a fixed position when forming an image, and forms an image by a single pass method by sequentially ejecting ink at predetermined intervals to different positions in the transport direction in accordance with the transport of the recording medium P. Note that the image formation mode by the head unit 24 may be a scan method instead of a single pass method.

[0031] 3 is a schematic diagram showing the configuration of the head unit 24. In FIG. 3, the ink ejection surface of the head unit 24 is shown.

[0032] Here, the head unit 24 includes four recording heads 240 attached to a mounting member 244. In the recording head 240, a plurality of image forming elements are arranged in a row along the width direction of the recording medium P, each having a pressure chamber (not shown) that stores ink, a piezoelectric element (not shown) provided on the wall of the pressure chamber, and a nozzle 243 that communicates with the pressure chamber. When a drive signal that causes the piezoelectric element to deform is input, the image forming element deforms the pressure chamber due to the deformation of the piezoelectric element, changing the pressure within the pressure chamber, and ejecting ink from the nozzle 243 that communicates with the pressure chamber. As a result, in each of the four recording heads 240, ink droplets of a liquid volume corresponding to the pixel value of the image data are ejected from the nozzle 243 toward the recording medium P, and an image is formed on the recording medium P carried by the transport drum 211.

[0033] The four recording heads 240 are arranged in a staggered pattern so that their arrangement range in the width direction of the recording medium P is continuous without interruption. The arrangement range in the width direction of the recording medium P of the nozzles 243 included in the four recording heads 240 covers the entire width in the width direction of the recording medium P in the area where an image is formed on the recording medium P transported by the transport drum 211. In other words, the head unit 24 forms a line head that can eject ink across the image formable width in the width direction of the recording medium P.

[0034] The recording head 240 is equipped with an ink heating unit (not shown) that heats the ink stored in the recording head 240, and ejects the heated ink in a sol state. When this sol ink is ejected onto the recording medium P, after the ink lands on the recording medium P, it quickly turns into a gel state and solidifies on the recording medium P due to natural cooling.

[0035] The type of ink ejected from the recording head 240 is arbitrary in the image forming apparatus 1 according to the present disclosure. For example, an ultraviolet-curable hot-melt ink composition can be used.

[0036] The fixing unit 25 has a UV irradiation unit arranged across the entire width of the recording medium P in the width direction of the conveyance unit 21. The fixing unit 25 irradiates the recording medium P placed on the conveyance unit 21 with energy rays such as ultraviolet rays from the UV irradiation unit to cure and fix the ink ejected onto the recording medium P. The fixing unit 25 is arranged between the position where the head unit 24 is arranged and the position where the delivery drum 261 of the delivery unit 26 is arranged.

[0037] The delivery unit 26 has a belt loop 262 having a circular belt supported by two rollers on the inside, and a cylindrical delivery drum 261 that delivers the recording medium P from the conveyance unit 21 to the belt loop 262. The delivery unit 26 delivers the recording medium P onto the belt loop 262 by the delivery drum 261, and then conveys the recording medium P by the belt loop 262 and sends it to the paper discharge unit 30.

[0038] The paper discharge unit 30 has a plate-shaped paper discharge tray 31 on which the recording medium P sent out by the delivery unit 26 is placed. The paper discharge unit 30 places the recording medium P on which an image has been formed on the paper discharge tray 31.

[0039] The colorimetric unit 50 measures the color of the image formed on the recording medium P by the image forming unit 20. The colorimetric unit 50 according to this embodiment is disposed, for example, downstream of the fixing unit 25, facing the conveying surface of the conveying drum 211.

[0040] The colorimetric unit 50, for example, uses a filter method to measure the color of the image formed on the recording medium P. The colorimetric unit 50 is configured to include, for example, a light-emitting element that emits light, a plurality of filters (for example, filters for each of the RGB colors) with different spectral transmittance characteristics, and a light-receiving element that receives reflected light through the filters.

[0041] The colorimetric data obtained by the colorimetric unit 50 is expressed, for example, in an RGB color space, with the color value for each pixel region being expressed as the density of 256 gradations of each RGB color.

[0042] The configuration of the colorimetric unit 50 can be modified in various ways. For example, the colorimetric unit 50 may be disposed as an independent device between the delivery unit 26 and the paper discharge unit 30. Furthermore, the colorimetric unit 50 may measure color using a spectrophotometric method instead of a filter method. Furthermore, instead of outputting color values ​​for each pixel area as pixel values ​​in an RGB color space, the colorimetric unit 50 may output color information for each pixel area as pixel values ​​in an Lab color space or another color space.

[0043] The color measurement unit 50 is provided with a temperature sensor 51 and a humidity sensor 52 for measuring the ambient temperature and humidity of the environment in which the recording medium P is placed. That is, the temperature sensor 51 and the humidity sensor 52 measure the ambient temperature and humidity of the environment in which the recording medium P is placed until the ink formed on the recording medium P stabilizes.

[0044] The locations of the temperature sensor 51 and the humidity sensor 52 can be changed as desired depending on the configuration of the image forming apparatus 1. For example, they may be disposed in the image forming unit 20 or in the external space.

[0045] 4 is a block diagram showing the configuration of a control system of the image forming apparatus 1. The image forming apparatus 1 includes a control unit 40, a color measurement unit 50, a storage unit 60, a head drive unit 70, a transport drive unit 80, an image processing unit 90, and an input / output interface 100.

[0046] The control unit 40 has a CPU 41, RAM 42, and ROM 43, and controls the overall operation of the image forming apparatus 1. The control unit 40 receives image data transmitted from an external device (e.g., a personal computer) connected to a communication network such as a LAN or WAN via the input / output interface 100. The control unit 40 then causes the head driving unit 70, the transport driving unit 80, the image processing unit 90, etc. to perform operations to form an image on the recording medium P based on this image data (input image data).

[0047] The CPU 41 reads out various control programs and setting data stored in the ROM 43, stores them in the RAM 42, and executes the programs to perform various arithmetic processing.

[0048] The RAM 42 provides a working memory space for the CPU 41 and stores temporary data. The RAM 42 may include a non-volatile memory.

[0049] The ROM 43 stores various control programs and setting data executed by the CPU 41. Instead of the ROM 43, a rewritable nonvolatile memory such as an EEPROM or a flash memory may be used.

[0050] Each of the functions (i.e., test printing and color measurement processing) of the control unit 40, which will be described later, is realized, for example, by the CPU 41 referring to control programs and various data stored in the ROM 42, RAM 43, and storage unit 60. However, some or all of the functions may be realized by processing by a DSP or dedicated hardware circuit instead of or in addition to processing by the CPU 41.

[0051] Additionally, the control unit 40 also has a timing means (for example, a counter circuit) so that when a test image is formed in test printing, the color measurement of the test image can be carried out periodically immediately after the image formation.

[0052] The head driving unit 70 receives image data that has been image-processed by the control unit 40, and forms a predetermined image on the recording medium P based on the image data. Specifically, under the control of the control unit 40, the head driving unit 70 applies a driving voltage to the head unit 24 according to the pixel values ​​of the image data. This causes ink to be ejected (spun out) from the nozzles 243 of the recording head 240 in an amount according to the pixel values ​​of the image data, and the ink lands at a predetermined position on the recording medium P, thereby forming an image.

[0053] The amount of ink ejected from the nozzles 243 of the recording head 240 is basically adjusted based on the voltage level of the drive voltage applied from the head drive unit 70 to each image forming element of the recording head 240. However, it can also be adjusted by correcting the ejection gradation (the number of ejections per pixel area) of each nozzle 243 of the recording head 240.

[0054] Based on a control signal supplied from the control unit 40, the transport drive unit 80 supplies a drive signal to a transport drum motor provided on the transport drum 211 to rotate the transport drum 211 at a predetermined speed and timing. In addition, based on a control signal supplied from the control unit 40, the transport drive unit 80 supplies a drive signal to motors for operating the medium supply unit 12, the delivery unit 22, and the delivery unit 26 to supply the recording medium P to the transport unit 21 and discharge the recording medium P from the transport unit 21.

[0055] The image processing unit 90 performs predetermined image processing on the image data to be printed, and stores the obtained image data in the storage unit 60. This image processing includes color conversion processing, tone correction processing, pseudo-halftoning processing, etc.

[0056] The input / output interface 100 is connected to an input / output interface of an external device (for example, a personal computer) and mediates the transmission and reception of data between the control unit 40 and the external device. The input / output interface 100 is configured, for example, by any one of various serial interfaces, various parallel interfaces, or a combination of these.

[0057] The storage unit 60 stores history data D1 (see FIG. 5) of color measurement results obtained in test printing that was previously performed, current print job data D2, etc. As the storage unit 60, for example, an HDD, DRAM, etc. are used.

[0058] [Details of the control unit configuration] The detailed configuration of the control unit 40 will be described below with reference to FIGS.

[0059] The image forming apparatus 1 (controller 40) according to this embodiment is configured to perform test printing as a calibration process before actual printing in order to perform density gradation correction and the like suitable for the image formation conditions, as in conventional methods. The image forming apparatus 1 then measures the color of the test image formed in the test printing using the colorimetric unit 50, and performs density gradation correction and the like for the input image data to be printed based on the obtained color values.

[0060] The test printing is typically performed under the same image forming conditions as those for the actual printing, which are stored in the print job data D2 to be performed.

[0061] Specifically, in test printing, for example, the combination of the type of ink ejected from the recording head 240 and the type of recording medium P is selected to be the same combination as in actual printing. Also, in test printing, the amount of UV light in the fixing unit 25, the heating temperature of the recording medium P in the heating unit 23, and the ink temperature in the recording head 240 are set to be the same conditions as in actual printing. In addition, in test printing, the ambient temperature and humidity of the environment around the recording medium P are set to be the same conditions as in actual printing.

[0062] In test printing, the control unit 40 forms, for example, a preset test image on the recording medium P using the image forming unit 20. The test image is, for example, a plurality of color charts with different hues and gradations (for example, patch images for each of RGB).

[0063] The control unit 40 then uses the colorimetry unit 50 to continuously measure the color of the image immediately after it is formed on the recording medium P in the test print, and identifies the color value of the image after color stabilization based on the time-series colorimetry data. For example, the control unit 40 identifies the colorimetry data obtained when the amount of change per unit elapsed time becomes equal to or less than a threshold as the final color value of the image formed on the recording medium P after color stabilization.

[0064] However, as mentioned above, if you actually wait until the ink dries on the recording medium P and the color values ​​stabilize each time you perform a test print, you will not be able to print during that waiting time, resulting in downtime.

[0065] Therefore, the control unit 40 according to this embodiment stores the measurement results obtained from each test print as history data D1. Then, the control unit 40 references the colorimetric results of the test print performed under the same or similar image forming conditions as the new test print from among the colorimetric results saved as history data D1, and if the colorimetric results are usable, identifies the color values ​​after color stabilization using the colorimetric results.

[0066] More specifically, the control unit 40 according to this embodiment compares the difference in the progression between the time-series colorimetric data obtained up to the present time for the image formed in the new test print and the time-series colorimetric data obtained for the image formed in the previous test print. If the difference in progression is equal to or less than a predetermined value, it determines that the colorimetric results obtained for the image formed in the previous test print are usable and concludes that the colorimetric measurement is complete at that point.

[0067] Here, the reason why colorimetry is actually performed temporarily on the image formed in the new test print before determining whether the colorimetry results from the previous test print can be used is because the color of the ink after stabilization varies depending on various factors. For example, even if inks containing the same main components are used, the color of the ink after stabilization may vary depending on differences in other components and additives. Furthermore, the color of the ink after stabilization may vary if the curing mode of the ink is different.

[0068] In this embodiment, for ease of explanation, a test print that is newly performed before the actual printing under the same image forming conditions as the actual printing will be referred to as the "current test print" or the "new test print." Also, a test print performed before the current test print will be referred to as the "previous test print."

[0069] FIG. 5 is a diagram showing an example of history data D1 stored in storage unit 60. As shown in FIG.

[0070] The history data D1 is data related to measurement results obtained from test printing carried out in the past. Specifically, the history data D1 stores, for example, "time-series colorimetric data," "color values ​​after image stabilization," and "image formation conditions" in association with each other for each test printing job carried out in the past.

[0071] Here, "time-series colorimetric data" refers to the color values ​​(e.g., RGB values) of an image at each elapsed time from immediately after image formation. Note that this colorimetric data may be stored as a color difference (e.g., a change from an initial value) relative to a reference color.

[0072] Furthermore, the "color value after stabilization of the image" is, for example, a color value identified when the amount of change in the color value per unit elapsed time becomes equal to or less than a threshold value based on time-series colorimetric data.

[0073] The "image formation conditions" store factors that affect the color value of the image and the color change of the image after image formation. Here, for example, the image formation conditions stored include "media type," "ink type," "UV light amount," "media heating temperature," "ink temperature," "ambient temperature," and "ambient humidity."

[0074] Here, "media type" refers to the type of recording medium P on which an image is formed. "Media type" is stored and managed separately for each recording medium P that differs in material, basis weight, thickness, etc.

[0075] Furthermore, the "ink type" is the type of ink ejected from the print head 240. The "ink type" is stored and managed separately for each ink, for example, with different ink components or additives. Note that when the ink lots are different, even if the ink has the same main components, the component ratio and viscosity may be slightly different due to changes over time or added components. For this reason, it is desirable to treat different ink lots as different ink types.

[0076] The "UV light amount" represents the amount of UV light applied by the fixing unit 25 to the image on the recording medium P for UV curing. The "media heating temperature" represents the heating temperature of the recording medium P when ink is ejected from the recording head 240, for example, the heating temperature of the recording medium P by the heating unit 23. The "ink temperature" represents the heating of the ink within the recording head 240. The "ambient temperature" and "ambient humidity" represent the ambient temperature and humidity of the environment in which the ejected ink is placed during the curing process. Here, the detected values ​​of the temperature sensor 51 and the humidity sensor 52 are stored. These factors change the curing state of the ink ejected on the recording medium P, and depending on the conditions, may cause the color value of the image after color stabilization to differ. From this perspective, these factors are stored and managed as separate image formation conditions in the history data D1.

[0077] An example of the processing performed by the control unit 40 will be described in more detail below.

[0078] Fig. 6 is a diagram showing an example of the operation flow of the control unit 40. The flowchart shown in Fig. 6 is, for example, a process executed by the control unit 40 in accordance with a computer program. For example, before carrying out actual printing, the control unit 40 carries out the following test printing under the same image formation conditions as the actual printing.

[0079] In step S1, the control unit 40 executes test printing under the same image forming conditions as those for the actual printing. Here, for example, patch images made up of the respective reference colors of RGB are used as the test images.

[0080] In step S2, the control unit 40 acquires the image formation conditions for this test printing. Here, the control unit 40 acquires, as the image formation conditions, information relating to, for example, the type of recording medium P and the type of ink ejected from the recording head 240. In addition, the control unit 40 acquires information relating to the amount of UV light from the fixing unit 25, the media heating temperature from the heating unit 23, the ink temperature from the recording head 240, the detected temperature from the temperature sensor 51, and the detected humidity from the humidity sensor 52.

[0081] In step S3, the control unit 40 determines whether or not there are any color measurement results obtained under image forming conditions that are the same as or similar to those of the current test print from among the color measurement results stored as history data D1. That is, the control unit 40 determines whether or not there are any color measurement results obtained under image forming conditions that are the same as or similar to those of the current test print from among the color measurement results obtained from test prints performed in the past.

[0082] If the history data D1 contains measurement results for image formation conditions that are the same as or similar to those of the current test print (S3: YES), the control unit 40 proceeds to step S7. On the other hand, if the history data D1 does not contain measurement results for image formation conditions that are the same as or similar to those of the current test print (S3: NO), the control unit 40 proceeds to step S4.

[0083] Here, the control unit 40 performs a process to check whether available measurement results exist in the history data D1 in order to quickly identify the post-stabilization color values ​​of the image formed in this test print. The processes in the following steps S4 to S6 are a normal colorimetry flow when available measurement results do not exist in the history data D1. On the other hand, the processes in steps S7 to S10 are a time-saving colorimetry flow when available measurement results exist in the history data D1.

[0084] In this step S3, if there are measurement results in the history data D1 that are the same as or similar to the image forming conditions for this test print (S3: YES), the control unit 40 sets the measurement results as the object to be referenced in step S9.

[0085] In step S3, if the history data D1 contains multiple measurement results under image formation conditions that are the same or similar to those of the current test print (S3: YES), the control unit 40 references, for example, the measurement result whose image formation conditions most closely match those of the current test print. In particular, the control unit 40 preferentially references colorimetric results in the history data D1 that used the same media type and ink type as those of the current test print. The control unit 40 then prioritizes similarities in terms of the UV light intensity of the fixing unit 25, the media heating temperature of the heating unit 23, the ink temperature of the recording head 240, the temperature detected by the temperature sensor 51, and the humidity detected by the humidity sensor 52.

[0086] In step S3, the control unit 40 may also refer to measurement results in the history data D1 that partially match the image formation conditions of the current test print, even if the image formation conditions do not completely match. Furthermore, the control unit 40 may also refer to measurement results with a high degree of similarity in the image formation conditions. In this case, a similarity determination method for image formation conditions may be set in advance, and the control unit 40 may refer to the measurement result in the history data D1 that is most similar to the image formation conditions of the current test print, based on the similarity determination method.

[0087] First, the normal color measurement flow of steps S4 to S6 will be described.

[0088] In step S4, the control unit 40 uses the color measurement unit 50 to perform color measurement of the test image.

[0089] At this time, if the color value of the test image obtained by color measurement indicates an abnormal value, the control unit 40 may interrupt this series of operation flow and notify the user.

[0090] In step S5, the control unit 40 refers to the colorimetric data obtained in step S4 and determines whether the color change between the currently obtained colorimetric data (color values) and the colorimetric data (color values) measured immediately before is within a threshold value. If the color change between the currently obtained colorimetric data and the colorimetric data measured immediately before is not within the threshold value (S5: NO), the control unit 40 returns to step S4 and performs colorimetric measurement again. On the other hand, if the color change between the currently obtained colorimetric data and the colorimetric data measured immediately before is within the threshold value (S5: YES), the control unit 40 proceeds to step S6.

[0091] As explained with reference to Figure 1, it takes some time for the color values ​​of an image (i.e., ink) to stabilize after image formation. Therefore, in steps S4 and S5, the control unit 40 periodically measures the color values ​​of the image immediately after image formation, monitors the amount of change in the color values ​​per unit elapsed time, and waits until the color values ​​stabilize. Note that the control unit 40 repeatedly executes the processes of steps S4 and S5, for example, at 10-second intervals.

[0092] In step S6, the control unit 40 determines the final color values ​​and stores the time-series colorimetric data in the memory unit 60. At this time, the control unit 40 also stores the image formation conditions for this test print and the finally determined color values ​​in the memory unit 60, in addition to the time-series colorimetric data (see FIG. 5). This marks the end of the normal colorimetric flow. Note that the data stored in the memory unit 60 in step S6 is added as new measurement results to the history data D1.

[0093] Next, the time-saving color measurement flow of steps S7 to S10 will be described.

[0094] FIG. 7 is a diagram illustrating the time-saving colorimetry flow of steps S7 to S10. The curves in FIG. 7 are graphs of time-series colorimetry data obtained for test images from past test prints, connected by straight lines. The plots in FIG. 7 represent the colorimetry data obtained for the test images from the current test print. Note that in FIG. 7, the colorimetry data (color values) at each measurement point are expressed as color differences relative to the color values ​​obtained from the initial measurement.

[0095] In step S7, the control unit 40 uses the color measurement unit 50 to perform color measurement of the image formed in this test printing.

[0096] At this time, if the color values ​​of the test image obtained by measurement indicate abnormal values, the control unit 40 may interrupt this series of operation flow and notify the user.

[0097] In step S8, the control unit 40 determines whether a predetermined time has elapsed since the image was formed by test printing. If the predetermined time has not elapsed (S8: NO), the control unit 40 returns to step S7 and performs color measurement again. On the other hand, if the predetermined time has elapsed (S8: YES), the control unit 40 proceeds to step S9.

[0098] The "predetermined time" in step S8 is a waiting time until the trend of the trajectory of color value changes depicted by the time-series colorimetric data becomes apparent to a certain extent. That is, the "predetermined time" is set to a timing (e.g., 3 minutes) appropriate for determining the degree of match between the trajectory of color value changes of the image formed in the current test print and the trajectory of color value changes of images formed in previous test prints. Note that the control unit 40 repeatedly executes the processes of steps S7 and S8 at 10-second intervals, for example, until the predetermined time has elapsed.

[0099] In step S9, the control unit 40 compares the time-series measurement data obtained for the test image of the current test print with the time-series measurement data obtained for the test image of the previous test print determined as the reference object in step S3. The control unit 40 then determines whether the difference in the color change transition between the two is within a predetermined value. If the difference in the color change transition between the two is within the predetermined value (S9: YES), the control unit 40 proceeds to step S10. On the other hand, if the difference in the color change transition between the two is not within the predetermined value (S9: NO), the control unit 40 proceeds to step S4.

[0100] In step S9, the control unit 40 calculates the difference between the measurement data for each measurement timing from immediately after the image is formed until a predetermined time has elapsed, and then determines whether the difference in the color change transition between the two is within a predetermined value based on the cumulative value of the differences from the measurement data.

[0101] However, the method for calculating the difference in color change transition between the two is arbitrary. For example, the degree of similarity between the transition curve indicated by the time-series measurement data obtained for the test image of the current test print and the transition curve indicated by the time-series measurement data obtained for the test image of a previous test print may be used as the difference in color change transition between the two. In this case, the difference in color change transition between the two may also be expressed as a ratio, etc.

[0102] If the difference in the color change progression between the two is not within a predetermined value (S9: NO), the process proceeds to step S4 because the image formed in the current test print is independently measured using the normal colorimetry flow. This is because, due to some factor in the image formation conditions, the behavior of color change until stabilization differs between the image formed in the current test print and the image formed in the previous test print.

[0103] In step S10, the control unit 40 determines the final color values ​​of the image formed in the current test print using the final color values ​​determined from the measurement results of the previous test print determined as the reference object in step S3, and completes the color measurement. This is because if the difference in the color change progression between the two is within a predetermined value (S9: YES), it is assumed that the image formed in the current test print will stabilize with the same behavior as the image formed in the previous test print. In other words, this makes it possible to quickly identify the stabilized color values ​​of the image formed in the current test print.

[0104] Through the above-described operational flow, the control unit 40 according to this embodiment can identify the color values ​​of the test image after color stabilization. This enables the control unit 40 to determine what color correction processing should be performed on the input image data when carrying out actual printing. Note that the color correction processing itself performed after this is the same as conventionally known methods, and therefore will not be described here.

[0105] [effect] As described above, the image forming apparatus according to this embodiment an image forming unit that forms an image on a recording medium by ejecting ink; a color measurement unit that performs color measurement of the image formed on the recording medium; a control unit that controls the operations of the image forming unit and the colorimetric unit, performs test printing, and continuously measures the color of the image immediately after the image is formed in the test printing, and identifies the color value of the image after color stabilization based on time-series colorimetric data; a storage unit that stores the color measurement results and image forming conditions of the test printing performed in the past as history data in association with each other; Equipped with The control unit When a new test print is performed and colorimetry of the image formed in the test print is continuously performed, Among the color measurement results stored as the history data, the color measurement results obtained under the image forming conditions that are the same as or similar to those of the new test print are referenced; If the difference in the progression between the time-series colorimetric data obtained up to the present time of the image formed in the new test print and the time-series colorimetric data of the referenced colorimetric result is less than a predetermined value, the colorimetric measurement is considered to be complete at that point.

[0106] Therefore, according to the image forming apparatus of this embodiment, it is possible to shorten the waiting time until the color values ​​of the image currently being measured after color stabilization are identified while maintaining accurate reproducibility under various usage conditions.

[0107] In addition, in the image forming apparatus according to this embodiment, When the control unit performs colorimetry of the image formed by the new test printing until the colorimetry is completed without using the colorimetry result stored as the history data, The colorimetry data of the image formed in the new test print in chronological order up to the completion of colorimetry and the color values ​​after color stabilization are stored in the memory unit as new colorimetry results in association with the image formation conditions in the new test print.

[0108] Therefore, according to the image forming apparatus of this embodiment, if color measurement is performed on image forming conditions that are not stored in the memory unit until the color has stabilized, the measurement results can be sequentially accumulated in the memory unit so that they can be used as a reference for other future printing.

[0109] The image forming apparatus according to the present disclosure is not limited to the above-described embodiment, but can be applied to various applications and modifications.

[0110] (Application example 1) When the control unit 40 completes colorimetry of the test image, it may output a report containing the time-series colorimetry data up to the completion of colorimetry of the image, the color values ​​after color stabilization, and the image formation conditions. The report may be output in any manner. For example, the report contents may be printed on paper or displayed on a monitor (not shown).

[0111] This allows the user to recognize the color measurement results of the test image before actual printing.

[0112] (Application example 2) 6, if the control unit 40 determines in step S9 that the colorimetry results of the history data D1 can be used, the control unit 40 may notify the user of this and wait for instructions from the user. That is, the control unit 40 may identify the color values ​​of the test image after color stabilization based on the colorimetry results of the history data D1 only if the user has given permission to use the colorimetry results of the history data D1.

[0113] This allows the user to change to a mode of use in which they wish to obtain color measurement data for a test image in normal color measurement mode after the colors have been stabilized.

[0114] (Application example 3) The control unit 40 may be configured to transmit the history data D1 stored in the storage unit 60 to an external management device (not shown) and register the history data D1 in a database of the external management device. In this case, the control unit 40 may also search for history data D1 obtained by other devices registered in the database of the external management device in step S3 of the processing of the flowchart in FIG.

[0115] This allows the history data D1 to be shared among multiple image forming devices. That is, if printing under image forming conditions that have not been performed on the image forming device itself has already been performed on another device, the control unit 40 can use the color measurement results obtained at that time after color stabilization in the time-saving color measurement mode.

[0116] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. [Industrial Applicability]

[0117] According to the image forming apparatus of the present invention, it is possible to specify, in a shorter time, the color values ​​of images formed under various usage conditions after color stabilization. [Explanation of symbols]

[0118] 1. Image forming device 10 Paper feed section 11 Paper feed tray 12 Media supply section 20 Image forming unit 21 Conveyor 22 units 23 Heating section 24 Head Unit 25 Fixing section 26 Delivery Department 30 Paper output section 31 Paper output tray 40 Control Unit 50 Color measurement section 51 Temperature Sensor 52 Humidity sensor 60 Storage section 70 Head drive unit 80 Conveyor drive unit 90 Image processing section 100 Input / Output Interface 211 Transport drum 221 Swing arm section 222 Drums 240 recording head 243 Nozzle 244 parts 261 Drums 262 Belt loop D1 Historical Data P Recording medium

Claims

1. an image forming unit that forms an image on a recording medium by ejecting ink; a color measurement unit that performs color measurement of the image formed on the recording medium; a control unit that controls the operations of the image forming unit and the colorimetric unit, performs test printing, and continuously measures the color of the image immediately after the image is formed in the test printing, and identifies the color value of the image after color stabilization based on time-series colorimetric data; a storage unit that stores the color measurement results and image forming conditions of the test printing performed in the past as history data in association with each other; Equipped with The control unit When a new test print is performed and colorimetry of the image formed in the test print is continuously performed, Among the color measurement results stored as the history data, the color measurement results obtained under the image forming conditions that are the same as or similar to those of the new test print are referenced; If the difference in the transition between the time-series colorimetric data obtained up to the present time of the image formed by the new test print and the time-series colorimetric data of the referenced colorimetric result is equal to or less than a predetermined value, the colorimetric measurement is completed at that point. Image forming device.

2. When the color measurement results of the history data are usable, the control unit specifies the color values ​​of the image formed in the new test printing after color stabilization based on the color values ​​of the image after color stabilization finally specified in the color measurement results of the history data. The image forming apparatus according to claim 1 .

3. The image forming conditions include a combination of the type of ink used in the image forming unit and the type of recording medium. The image forming apparatus according to claim 1 .

4. The image forming conditions include a UV light amount in a UV curing process for the image formed on the recording medium. The image forming apparatus according to claim 1 .

5. The image forming conditions include a heating temperature of the recording medium when an image is formed in the image forming unit. The image forming apparatus according to claim 1 .

6. The image forming conditions include an ink temperature of the ejected ink when the image is formed in the image forming unit. The image forming apparatus according to claim 1 .

7. The image forming conditions include the ambient temperature and humidity of the surrounding environment of the image forming unit or the color measurement unit. The image forming apparatus according to claim 1 .

8. When the control unit completes colorimetry of the image formed by the new test printing, the control unit outputs, as a report, the colorimetry data in chronological order up to the completion of colorimetry of the image, the color values ​​after color stabilization, and the image forming conditions. The image forming apparatus according to claim 1 .

9. If the color measurement results of the history data are usable, the control unit notifies the user of that fact, and if permitted by the user, identifies the color values ​​of the image formed by the new test printing after color stabilization based on the color measurement results of the history data. The image forming apparatus according to claim 1 .

10. The control unit transmits the history data stored in the storage unit to an external management device and registers the history data in a database of the external management device. The image forming apparatus according to claim 1 .

11. If the colorimetry results stored as the history data do not include any that employ the same or similar image formation conditions as the new test print, and if the difference in transition between the time-series colorimetry data obtained up to the present time of the image formed in the new test print and the time-series colorimetry data of the referenced measurement results is greater than the predetermined value, the control unit continues to perform colorimetry until the amount of change per unit elapsed time of the color value of the image formed in the new test print becomes equal to or less than a threshold value. The image forming apparatus according to claim 1 .

12. When the control unit performs colorimetry of the image formed by the new test printing until the colorimetry is completed without using the colorimetry result stored as the history data, The color measurement data in time series up to the completion of color measurement of the image formed in the new test printing and the color values ​​after color stabilization are stored in the storage unit as new color measurement results in association with the image formation conditions in the new test printing. The image forming apparatus according to claim 1 .

13. A control method for an image forming apparatus, which performs test printing and continuously measures the color of the image immediately after the image is formed on a recording medium in the test printing, and specifies color values ​​of the image after color stabilization based on time-series color measurement data, In a storage unit that associates colorimetry results with image forming conditions for the test printing that has been performed in the past and stores them as history data, the colorimetry results of the test printing that have been performed under image forming conditions that are the same as or similar to those of the new test printing are referenced from among the colorimetry results stored as the history data; If the difference in the transition between the time-series colorimetric data obtained up to the present time of the image formed by the new test print and the time-series colorimetric data of the referenced colorimetric result is equal to or less than a predetermined value, the colorimetric measurement is completed at that point. Control method.

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