Image forming apparatus

Abstract

To appropriately control density of an image formed by an image forming apparatus.SOLUTION: An image forming apparatus 100 includes: an image forming engine 101 that forms an image on the basis of an image forming condition; an intermediate transfer body on which the image forming engine 101 forms a pattern image; an image density sensor 230 that reads the pattern image on the intermediate transfer body; an image forming condition generation section 370 that generates the image forming condition on the basis of a reading result of the pattern image by the image density sensor 230; and a predicted density calculation section 305 that determines data about a change in image density with lapse of time and updates the image forming condition on the basis of the data. When a condition for forming the pattern image is satisfied after the predicted density calculation section 305 updates the image forming condition, the image forming engine 101 forms the pattern image on the basis of the image forming condition generated by the image forming condition generation section 370 before the update by the predicted density calculation section 305.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, such as a printer, a copying machine, a multifunction machine, or a facsimile machine, which forms an image on a sheet. [Background technology]

[0002] An image forming apparatus may be unable to maintain the quality of an image printed on a sheet (image density, gradation, etc.) due to short-term fluctuations in image formation conditions caused by environmental fluctuations, or long-term fluctuations in image formation conditions caused by aging of components, etc. Environmental fluctuations are fluctuations in environmental conditions (temperature, humidity, etc.) inside and outside the image forming apparatus. Components, etc. are image carriers and developers that are directly involved in image formation.

[0003] In order to adjust image density and gradation, image forming apparatuses need to correct image forming conditions from time to time in response to various variable factors. The process of appropriately correcting changes in image density and gradation is generally called "calibration." For example, image forming apparatuses adjust image density and gradation (perform calibration) by forming a pattern image for calibration on an image carrier and correcting image forming conditions based on the results of reading this pattern image.

[0004] The image forming apparatus disclosed in Patent Document 1 performs calibration without forming a pattern image based on the state of the apparatus and environmental conditions. In this case, the image forming apparatus predicts gradation pattern information, which is the result of reading a pattern image for gradation calibration, based on the state of the apparatus and environmental conditions, and performs calibration based on the predicted gradation pattern information. Calibration (predictive control) based on prediction of gradation pattern information can be performed, for example, even during continuous printing, since image formation and image reading are not required. In addition, since there is no consumption of developer by calibration, it can be performed frequently. However, calibration (predictive control) based on prediction of gradation pattern information does not necessarily produce highly accurate results because it depends on the prediction method, the number of learning data used in machine learning, and the coverage of environmental conditions, etc.

[0005] Calibration using a pattern image (actual measurement control) has high correction accuracy, but leads to reduced productivity and increased developer consumption. Therefore, actual measurement control cannot be performed frequently. By adopting both actual measurement control and predictive control, calibration can be performed while maintaining productivity and reducing developer consumption. In this case, predictive control is performed more frequently than actual measurement control. Actual measurement control is performed less frequently than predictive control, but is performed periodically.

[0006] Even if the predictive control is not performed properly, the image formation conditions are reset properly by periodically performing calibration (actual measurement control) using a pattern image. After that, the predictive control is performed based on the image formation conditions reset by the actual measurement control. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2019-74574 A Summary of the Invention [Problem to be solved by the invention]

[0008] When both the actual measurement control and the predictive control are adopted, the same image formation conditions are updated in either case, so that when a pattern image is formed, the pattern image is formed based on the image formation conditions updated by the predictive control.

[0009] When the prediction accuracy of predictive control is low, an error occurs in the prediction result. If this error accumulates, the image formation conditions may deviate significantly from the optimal conditions. When calibration (actual measurement control) is performed using a pattern image under such image formation conditions, the density change before and after the actual measurement control is performed may be noticeable in the image, or it may take a long time to stabilize the image density to the target density. As a result, in an image forming apparatus in which both actual measurement control and predictive control are performed, the image density may not be appropriately controlled if the prediction accuracy of predictive control is low.

[0010] SUMMARY OF THE PRESENT DISCLOSURE In view of the above problems, a main object of the present invention is to appropriately control the density of an image formed by an image forming apparatus. [Means for solving the problem]

[0011] The image forming apparatus of the present invention is an image forming apparatus that forms an image on a sheet, and comprises: an image forming means that forms an image based on image formation conditions; an image carrier on which a pattern image is formed by the image forming means; a reading means that reads the pattern image on the image carrier; a generation means that generates the image formation conditions based on the reading results of the pattern image by the reading means; and an update means that determines data regarding changes in image density over time and updates the image formation conditions based on the data, and is characterized in that when conditions for forming a pattern image are satisfied after the image formation conditions are updated by the update means, the image forming means forms the pattern image based on the image formation conditions generated by the generation means before the update by the update means. Effect of the Invention

[0012] According to the present invention, it is possible to appropriately control the density of an image formed by an image forming apparatus. [Brief description of the drawings]

[0013] [Figure 1] FIG. [Diagram 2]FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Diagram 3] A diagram of the scanner configuration. [Figure 4] FIG. [Diagram 5] FIG. 4 is a diagram for explaining the controller process (comparison example). [Figure 6] FIG. [Figure 7] FIG. [Figure 8] 4 is a flowchart showing actual measurement control. [Figure 9] 4A and 4B are flowcharts showing automatic tone correction and actual measurement control. [Figure 10] 1 is a flowchart showing predictive control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] A preferred embodiment of the present invention will be described below with reference to the attached drawings. Note that while the present embodiment will be described using an electrophotographic method, the characteristic points of control, particularly the matters described in the claims, have the same problems as inkjet printers and dye-sublimation printers, and the problems can be solved using the methods described below. Therefore, we assert that the above claims are within the scope of the patent claims for each image forming apparatus.

[0015] (Configuration of Image Forming Apparatus) 1 is an explanatory diagram of a controller that controls the overall operation of the image forming apparatus 100. A controller 300 is connected to an operation panel 191, an external memory 181, an image forming engine 101, and a scanner 171.

[0016] The controller 300 includes an input / output buffer 301, an input / output I / F unit 309, a memory I / F unit 310, and a scanner I / F unit 318. The controller 300 includes a first central processing unit (CPU) 313, a storage 302, a random access memory (RAM) 309, and a read only memory (ROM) 380. The controller 300 includes a raster image processor (RIP) unit 312, a color processing unit 313, a tone correction unit 314, a pseudo halftone processing unit 315, and an engine I / F unit 316. These components of the controller 300 are connected to a system bus 317 and can transmit and receive data to and from each other.

[0017] The input / output I / F unit 309 controls communication with the operation panel 191. The operation panel 191 is a user interface equipped with an input interface and an output interface. The input interface is various key buttons, a touch panel, etc. The output interface is a display, a speaker, etc. A user can input print instructions, correction process execution instructions, etc. to the image forming apparatus 100 through the input interface of the operation panel 191. A user can check the operating status and notifications of the image forming apparatus through the output interface of the operation panel 191. The input / output I / F unit 309 accepts instructions, etc. input through the operation panel 191, and outputs various information through the operation panel 191.

[0018] The memory I / F unit 310 controls communication with the external memory 181. The external memory 181 is used to store print data and various information of the image forming apparatus 100. The input / output buffer 301 temporarily stores data transmitted and received by the input / output I / F unit 309 and the memory I / F unit 310. The scanner I / F unit 318 controls communication with the scanner 171, which is an image reading device. The scanner 171 reads an image of a document when instructed to read the document by the controller 300 via the scanner I / F unit 318, and generates image data. The image data generated by the scanner 171 is stored in the RAM 307. The configuration of the scanner 171 will be described in detail later.

[0019] The first CPU 311 starts up by executing a boot program stored in the ROM 380, and controls the operation of the image forming apparatus 100 by executing a computer program (control program) stored in the storage 302. The RAM 307 provides a working area when the first CPU 311 executes the computer program. The RAM 307 is used for control codes, calculations required for data interpretation and printing, or processing of print data. The storage 302 stores control data in addition to the control program. The storage 302 stores computer programs that function as an image information generating unit 303, a maximum density condition determining unit 304, a predicted density calculating unit 305, and a gradation correction table generating unit 306 by being executed by the first CPU 311. The storage 302 is a large-capacity storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive).

[0020] An image information generating unit 303 generates various image objects according to data acquired from an external computer. A maximum density condition determining unit 304 performs maximum density adjustment. A predicted density calculating unit 305 predicts image density based on a detection result (signal value) of a sensor 340 (described later) provided in the image forming engine 101. A gradation correction table generating unit 306 generates a gradation correction table (γLUT (Look Up Table)) used for gradation correction of an image. A RAM 307 includes a table storage unit 308 that temporarily stores the processing results by the maximum density condition determining unit 304, the predicted density calculating unit 305, and the gradation correction table generating unit 306.

[0021] The RIP unit 312 generates image data by expanding the image object generated by the image information generation unit 303 into a bitmap image. The color processing unit 313 performs multidimensional color conversion processing on the image data. The gradation correction unit 314 converts the image data after color conversion processing based on a γLUT. The gradation correction unit 314 converts the image data of each color component based on a γLUT corresponding to each color component. The γLUT functions as a conversion condition for converting the image data. The pseudo-halftone processing unit 315 performs pseudo-halftone processing such as a dither matrix or error diffusion method on the image data after the gradation correction.

[0022] The image data processed by the RIP unit 312, color processing unit 313, tone correction unit 314, and pseudo halftone processing unit 315 is transmitted to the image forming engine 101 via an engine I / F unit 316. The image forming engine 101 forms an image based on image data obtained from the controller 300.

[0023] The image forming engine 101 includes a second CPU 102, a sensor 340, a timer 350, a counter 360, and an image density sensor 230. The second CPU 102 controls an image forming process (printing process) on a sheet based on image forming conditions. Signal values ​​output from the sensor 340, the timer 350, and the counter 360 are used for image density prediction processing by the predicted density calculation unit 305. The sensor 340 is an environmental sensor provided inside the image forming apparatus 100, for example, and detects environmental information (temperature, humidity, etc.) of the image forming apparatus 100. The timer 350 is used to measure time such as a printing interval. The counter 360 is used to count the number of printed sheets, for example. In this way, the sensor 340, the timer 350, and the counter 360 are detection units that detect the environmental conditions of the image forming apparatus 100, and the signal values ​​output from each of them indicate changes in the environmental conditions during image formation. The image density sensor 230 will be described later.

[0024] The printing process is not limited to using image data obtained by the RIP unit 312, and in the case of copying process, image data generated by reading an original by the scanner 171 is used. Also, when printing a pattern image for calibration, printing is performed using image data (detection image data) generated by the first CPU 311 on the RAM 307.

[0025] 2 is a configuration diagram of image forming apparatus 100. Image forming apparatus 100 includes a housing 201 incorporating image forming engine 101 and controller 300. Image forming engine 101 includes a mechanism for image formation in addition to the configuration described in FIG. 1. Printing process processing (e.g., image formation processing, paper feeding processing, etc.) by the mechanism for image formation is controlled by second CPU 102. A scanner 171 and an operation panel 191 are provided on the upper part of housing 201.

[0026] The mechanisms for image formation in this embodiment include an optical processing mechanism 110, a fixing processing mechanism 120, a paper feeding processing mechanism 130, and a transport processing mechanism 140. The optical processing mechanism 110 forms an electrostatic latent image, visualizes the electrostatic latent image, and transfers the visualized image to a sheet S. The fixing processing mechanism fixes the transferred visualized image to the sheet S. The paper feeding processing mechanism feeds the sheet S. The transport processing mechanism transports the fed sheet S.

[0027] The optical processing mechanism 110 includes image forming units 220, 221, 222, and 223, an intermediate transfer body 252, and a secondary transfer roller 251. The image forming units 220, 221, 222, and 223 have the same configuration and are used to form images of different colors. In this embodiment, the image forming unit 220 is used to form an image of yellow (Y). The image forming unit 221 is used to form an image of magenta (M). The image forming unit 222 is used to form an image of cyan (C). The image forming unit 223 is used to form an image of black (K).

[0028] Each of the image forming units 220, 221, 222, and 223 includes a photosensitive drum 205, a charger 211, a laser scanner 207, and a developer 212. The photosensitive drum 205 is a photoconductor having a photosensitive layer on its surface, and rotates counterclockwise around the drum axis in the drawing. The charger 211 uniformly charges the surface of the rotating photosensitive drum 205. The laser scanner 207 irradiates the charged surface of the photosensitive drum 205 with laser light, thereby forming an electrostatic latent image on the surface of the photosensitive drum 205.

[0029] The laser scanner 207 includes a light source that outputs laser light, a laser driver that controls on / off of the laser light output from the light source based on image data acquired from the controller 300, a laser output unit 208 including a rotating polygon mirror, and a reflecting mirror 209. The laser light output from the light source is reflected by the rotating polygon mirror and the reflecting mirror 209 and irradiates the surface of the photosensitive drum 205. At this time, as the rotating polygon mirror rotates, the laser light repeatedly moves in one direction. As the laser light moves in one direction, the irradiation position of the laser light on the surface of the photosensitive drum 205 moves in one direction. As a result, an electrostatic latent image for one line is formed on the surface of the photosensitive drum 205.

[0030] In this embodiment, the direction in which the irradiation position of the laser light on the surface of the photosensitive drum 205 moves is the axial direction of the photosensitive drum 205. Therefore, the axial direction of the photosensitive drum 205 is the main scanning direction. As the laser light repeatedly moves in the main scanning direction and the photosensitive drum 205 rotates, an electrostatic latent image of multiple lines is repeatedly formed on the surface of the photosensitive drum 205. As a result, an electrostatic latent image that spreads in the main scanning direction and in a sub-scanning direction that intersects with the main scanning direction is formed on the surface of the photosensitive drum 205.

[0031] The developing device 212 visualizes the electrostatic latent image into a toner image using a developer of a corresponding color (toner in this case). As a result, a yellow toner image is formed on the photosensitive drum 205 of the image forming unit 220. A magenta toner image is formed on the photosensitive drum 205 of the image forming unit 221. A cyan toner image is formed on the photosensitive drum 205 of the image forming unit 222. A black toner image is formed on the photosensitive drum 205 of the image forming unit 223.

[0032] The toner image on each photosensitive drum 205 is transferred onto the intermediate transfer body 252 to which a voltage of the opposite polarity to the toner is applied. The intermediate transfer body 252 is an endless belt-like image carrier that rotates in a clockwise direction in the figure. The toner images of each color are transferred onto the intermediate transfer body 252 in a superimposed manner by sequentially transferring the images according to the relationship between the position of each photosensitive drum 205 and the rotation speed of the intermediate transfer body 252. As a result, a full-color toner image is carried on the intermediate transfer body 252. When a black-and-white image is formed, only the image forming unit 223 that forms a black image operates, and the black image is transferred onto the intermediate transfer body 252. The intermediate transfer body 252 conveys the transferred toner image to the secondary transfer roller 251 by rotating.

[0033] An image density sensor 230 is disposed near the intermediate transfer body 252 and downstream of the image forming unit 223 in the rotation direction of the intermediate transfer body 252. The image density sensor 230 is a reading device that reads a pattern image for calibration carried on the intermediate transfer body 252. The result of reading the pattern image by the image density sensor 230 is used for calibration to adjust the density of the image formed by the image forming engine 101.

[0034] The paper feed processing mechanism 130 includes a storage case 210 that stores sheets S. The paper feed processing mechanism 130 feeds the sheets S stored in the storage case 210 one by one and transports them to the transport processing mechanism 140. The transport processing mechanism 140 transports the sheet S fed from the paper feed processing mechanism 130 to a secondary transfer roller 251. At that time, the transport processing mechanism 140 corrects skew of the sheet S and transports the sheet S to the secondary transfer roller 251 in accordance with the timing at which the toner image carried on the intermediate transfer body 252 is transported to the secondary transfer roller 251.

[0035] The secondary transfer roller 251 presses the sheet S against the intermediate transfer body 252 and at the same time applies a voltage of the opposite polarity to that of the toner. This causes the secondary transfer roller 251 to collectively transfer the toner images of each color carried by the intermediate transfer body 252 to the sheet S. The secondary transfer roller 251 transports the sheet S to which the toner images have been transferred to the fixing process mechanism 120.

[0036] The fixing process mechanism 120 includes a fixing device 260. The fixing device 260 has two rollers, at least one of which has a heat source. The fixing device 260 sandwiches and conveys the sheet S, onto which the toner image has been transferred, between the two rollers. The two rollers heat and press the toner image with the heat source, thereby melting and fixing the toner image to the sheet S. As a result, an image is printed on one side of the sheet S. In the case of single-sided printing, the sheet S is discharged from the fixing device 260 to the paper discharge section 280.

[0037] In the case of double-sided printing, the sheet S is conveyed again to the secondary transfer roller 251 via the inversion unit 270. Since the print side of the image on the sheet S is inverted by the inversion unit 270, the toner image is transferred to the other side by the secondary transfer roller 251. Thereafter, the toner image is fixed on the sheet S by the fixing device 260, and the sheet S is discharged to the paper discharge unit 280. Printing on the sheet S is performed in this manner.

[0038] 3 is a configuration diagram of scanner 171. Scanner 171 includes an automatic document feeder (ADF) 413 and a reading unit 414. ADF 413 includes document tray 400 on which documents are placed, pickup roller 404, transport roller 406, discharge roller 409, and discharge tray 410. ADF 413 transports the documents placed on document tray 400 by pickup roller 404 and transport roller 406, and discharges the documents to discharge tray 410 by discharge roller 409. The documents are read while being transported from transport roller 406 to discharge roller 409. A document passage detection sensor 405 is provided on the transport path along which the documents are transported.

[0039] The document tray 400 is provided with a document presence / absence sensor 402 for detecting the presence or absence of a document, two document guides 401, and a document size detection sensor 403. The document presence / absence sensor 402 is provided at the base end portion of the document tray 400. The two document guides 401 are provided so as to be parallel to each other in a direction (width direction) intersecting the document transport direction. The document guide 401 regulates the width direction of the documents loaded on the document tray 400. The document size detection sensor 403 is used to detect the length of the documents in the transport direction (document length). Depending on whether the document size detection sensor 403 detects a document loaded on the document tray 400, it is detected whether the document length is longer than the length from the base end of the document tray 400 to the position of the document size detection sensor 403.

[0040] Pickup roller 404 is a roller for supplying documents loaded on document tray 400 one by one to a transport path inside ADF 413. The documents supplied by pickup roller 404 are detected by document passing detection sensor 405. The completion of passage of one document is determined based on the detection time of the document by document passing detection sensor 405. Transport roller 406 transports the document supplied by pickup roller 404. Discharge roller 409 discharges the document transported by transport roller 406 to discharge tray 410. Although not shown in the figure, transport roller 406, pickup roller 404, and discharge roller 409 are all driven by a stepping motor as a drive source.

[0041] The reading unit 414 includes a flow reading glass 407 and a document table glass 412 on the surface of the housing facing the ADF 413, and includes a sensor unit 411 inside the housing. The sensor unit 411 has a CIS (Contact Image Sensor) 408. An original conveyed by the ADF 413 passes above the flow reading glass 407. The sensor unit 411 is located directly below the flow reading glass 407, and reads the original passing over the flow reading glass 407.

[0042] The sensor unit 411 is disposed so that the longitudinal direction of the CIS 408 intersects with the document transport direction. The sensor unit 411 reads the document using a direction intersecting the document transport direction as the main scanning direction. The document transport direction is the sub-scanning direction. The sensor unit 411 is movable in the sub-scanning direction. The flow reading glass 407 has a predetermined length in the sub-scanning direction. The sensor unit 411 can read the document by moving the CIS 408 to a predetermined position within the range of the flow reading glass 407 in the sub-scanning direction.

[0043] The CIS 408 has a light source that can irradiate the document with linear light in the main scanning direction through the flow reading glass 407. The light source is configured by arranging a plurality of light emitting elements such as LEDs (Light Emitting Diodes) in a line in the main scanning direction. The CIS 408 is configured by arranging a plurality of photoelectric conversion elements such as CCDs (Charge Coupled Devices) in the main scanning direction. Light emitted from the light source and reflected by the document is received by the photoelectric conversion elements. The photoelectric conversion elements convert the received light into an electrical signal.

[0044] The CIS 408 has a memory that temporarily stores the electrical signal generated by the photoelectric conversion element, and an ASIC (application specific integrated circuit) that controls the operation of the CIS 408. The ASIC controls the reading operation by the light source and the photoelectric conversion element. The ASIC also performs a predetermined process on the electrical signal stored in the memory to generate image data representing the read image. As described above, the CIS 408 can perform a reading operation to read an image of a document.

[0045] The sensor unit 411 can read an original document conveyed by the ADF 413 via the flow reading glass 407, and can also read an original document placed on the original platen glass 412. When reading an original document placed on the original platen glass 412, the sensor unit 411 performs a reading operation by the CIS 408 while moving in the sub-scanning direction. The reading operation is the same as when reading an image of an original document conveyed by the ADF 413 via the flow reading glass 407.

[0046] (calibration) The image forming apparatus 100 of this embodiment can perform calibration through the following three types of processing. In the first process, the image forming apparatus 100 forms a pattern image (detection image) for calibration (tone correction) on the intermediate transfer body 252, and reads this pattern image with the image density sensor 230. The image forming apparatus 100 generates (updates) a γLUT based on the result of reading the pattern image with the image density sensor 230, and performs tone correction. Hereinafter, the first process will be referred to as "actual measurement control." In the second process, the image forming apparatus 100 predicts an image density value of a pattern image when the image forming apparatus 100 forms the pattern image on the sheet S, based on fluctuations in environmental conditions such as temperature and humidity, and the states of the components. The image forming apparatus 100 updates the γLUT based on the predicted image density value, and performs gradation correction. Hereinafter, the second process will be referred to as "predictive control." In the third process, the image forming apparatus 100 prints a pattern image for calibration (tone correction) on the sheet S, and reads the pattern image printed on the sheet S with the scanner 171. The image forming apparatus 100 performs tone correction based on the result of reading the pattern image with the scanner 171.

[0047] 4 is an exemplary diagram of a pattern image (detection image) formed on intermediate transfer body 252 in actual measurement control of this embodiment. The pattern image is composed of a plurality of patch images (10 in this example) each having a different gradation (image density). The patch images of each image density pass sequentially through the detection position of image density sensor 230 as intermediate transfer body 252 rotates. Image density sensor 230 reads the patch images passing through the detection position and detects the image density value.

[0048] FIG. 5 is a process explanatory diagram of a controller for performing calibration (actual measurement control and predictive control) as a comparative example. The image forming engine 101 includes an image forming condition generating unit 370 in addition to the configuration described in FIG. 1. The second CPU 102 includes a patch output unit 501 and a patch reading unit 502. The patch output unit 501 controls the image forming engine 101 to form a pattern image. The patch reading unit 502 acquires the result of reading the pattern image by the image density sensor 230. The image forming condition generating unit 370 generates image forming conditions using the value of γLUT 503 acquired from the controller 300. The RAM 307 holds a γLUT (Look Up Table) 503, an actual measurement control target 504, and a predicted reference density 505 in addition to the configuration described in FIG. 1.

[0049] When performing actual measurement control, the second CPU 102 (patch output unit 501) of the image forming engine 101 forms a toner image of a pattern image on the intermediate transfer body 252 by the image forming engine 101 under image forming conditions based on the γLUT 503 acquired from the controller 300. The second CPU 102 (patch reading unit 502) notifies the tone correction table generating unit 306 of the controller 300 of the image density of the toner image on the intermediate transfer body 252 read by the image density sensor 230. The first CPU 311 updates the predicted reference density 505 based on the detection result (image density data) of the image density of the toner image notified from the second CPU 102. The predicted reference density 505 becomes a reference value when acquiring a predicted value of the image density (predicted density value) during predictive control.

[0050] The first CPU 311 updates the γLUT 503 based on the image density data notified by the gradation correction table generation unit 306, the current γLUT 503 stored in the RAM 307, and the actual measurement control target 504. The actual measurement control target 504 is a target value of the γLUT by actual measurement control. When performing normal printing on the sheet S in accordance with a print job, the first CPU 311 performs gradation correction by the gradation correction unit 314 with reference to the γLUT 503.

[0051] When performing predictive control, the second CPU 102 of the image forming engine 101 notifies the controller 300 of predictive elements used to predict the image density value of the pattern image. The predictive elements in this embodiment are information such as the detection result of the sensor 340, the count value of the counter 360, and the image forming conditions generated by the image forming condition generating unit 370. The first CPU 311 of the controller 300 calculates a predicted density value by the predicted density calculation unit 305 according to a previously learned prediction model based on the notified predictive elements and the predicted reference density 505 updated by the actual measurement control, and notifies the gradation correction table generating unit 306 of the predicted density value. The first CPU 311 updates the γLUT 503 by the gradation correction table generating unit 306 in the same manner as in the actual measurement control.

[0052] As described above, the same γLUT 503 is finally updated in both actual measurement control and predictive control. That is, the pattern image used in actual measurement control is formed using the γLUT 503 updated by predictive control. In a configuration in which both actual measurement control and predictive control are performed, correction by predictive control, which can be performed in a short time and does not consume toner, is performed more frequently than actual measurement control, and actual measurement control, which has high correction accuracy, is performed less frequently than predictive control. However, predictive control does not necessarily provide high-precision correction. Therefore, it is necessary to return the γLUT 503 and the predicted reference density 505 of the subsequent predictive control to an appropriate state by regular actual measurement control.

[0053] Examples of cases in which predictive control cannot provide highly accurate predictions include when the image forming apparatus 100 is operated in an environment outside the learned data or when the amount of learned data is insufficient. Frequent predictive control under such circumstances is expected to cause prediction errors to accumulate, and the value of γLUT503 to gradually deviate from the appropriate value. As described above, the image forming apparatus 100 attempts to return γLUT503 to an appropriate state by performing actual measurement control. However, when a pattern image is formed using an inappropriate γLUT503, the value of γLUT503 does not return to an appropriate value even when actual measurement control is performed.

[0054] The first problem is as follows. When an inappropriate γLUT 503 is used, the image density of the formed pattern image may not be suitable for actual measurement control. Therefore, the image density of the pattern image detected by the patch reading unit 502 becomes a value that deviates from the actual measurement control target 504. In this case, the amount of fluctuation of the γLUT 503 due to the correction becomes large, and the error becomes large accordingly.

[0055] The second problem is as follows. The image density detected by performing actual measurement control is saved as a predicted reference density 505 for subsequent predictive control. The predicted reference density 505 is updated based on the image density detected from a pattern image based on the state before the γLUT 503 is updated. Therefore, if an inappropriate γLUT 503 is used, the predicted reference density 505 is updated to a value that is deviated from the appropriate value. With an image density value predicted based on such a predicted reference density 505, there is a possibility that it will be impossible to predict the image density with high accuracy thereafter.

[0056] The third problem is as follows. In actual measurement control, the γLUT503 is not updated using the detected image density value itself, but a feedback rate is set, and the amount of correction can be suppressed according to a value obtained from the image density value and the feedback rate. This is because actual measurement control can be performed even with a small number of patch images, and it is desirable to set a feedback rate and gradually update γLUT503 in the case of simple correction with one patch image, assuming that the accuracy is lower than when there are a large number of patch images. In other words, if actual measurement control with a low feedback rate is performed in a state in which γLUT503 is deviated from the appropriate state by predictive control, it is difficult to update γLUT503 to the appropriate state with one actual measurement control.

[0057] In this embodiment, in order to cope with these problems that arise when sufficient correction accuracy cannot be obtained by predictive control, the actual measurement control is prevented from being affected by predictive control.

[0058] 6 is a diagram for explaining the process of the controller for performing the calibration (actual measurement control and predictive control) of this embodiment. Compared with the process explanatory diagram of FIG. 5 (comparative example), the following points are different. The RAM 307 is provided with a γLUT 506 in addition to the γLUT 503. The tone correction table generation unit 306 updates the γLUT 503 and the γLUT 506 . The tone correction table generator 306 uses the γLUT 506 during actual measurement control.

[0059] The γLUT 503 is used for the purpose of performing gradation correction by being referred to by the gradation correction unit 314 during normal printing. The γLUT 506 is used for the purpose of being referred to by the patch output unit 501 during the next actual measurement control to output a pattern image (patch image) for correction.

[0060] Each data on the RAM 307 is saved in the storage 302 at a specific timing. The specific timing is when each data is updated, or when a shutdown process is performed or when the device transitions to a sleep state. The data saved in the storage 302 is expanded in the RAM 307 at the next startup.

[0061] Fig. 7 is a process explanatory diagram of a controller for performing predictive control in this embodiment. The data flow is different from that in the process explanatory diagram of Fig. 6. In predictive control, γLUT506 used in actual measurement control is not updated, and only γLUT503 is updated. γLUT503 is used as a correction time γLUT that the tone correction table generating unit 306 refers to during predictive control. As a result, γLUT503 is updated by predictive control and is applied to normal printing according to the print job. Since γLUT506 is not updated, it is used in the next actual measurement control without being affected by the results of predictive control.

[0062] FIG. 8 is a flowchart showing the actual measurement control.

[0063] The first CPU 311 notifies the image forming engine 101 of a value extracted from the γLUT 506 to be used for a pattern image (patch image) to be output by actual measurement control (S701). This process is performed once when the image forming apparatus 100 is started up or when it returns from a sleep state. The image forming engine 101 stores the notified data in a memory (not shown). For example, when outputting a patch image with a cyan pixel value of 120, the first CPU 311 notifies the image forming engine 101 of the 120th index value of the cyan γLUT. This enables the image forming engine 101 to form a patch image with an image density based on that value.

[0064] The first CPU 311 determines whether the execution conditions for the actual measurement control are satisfied by the image forming engine 101 (S702). The execution conditions for the actual measurement control are, for example, the number of sheets printed since the previous actual measurement control, or the start-up time after the power has been cut off for a certain period of time. The number of sheets printed is counted by the counter 360, and if the count value is equal to or greater than a predetermined number of sheets, it is determined that the execution conditions are satisfied. Note that the execution conditions for the actual measurement control may be other than the above. For example, it may be determined that the execution conditions are satisfied if the time elapsed since the previous actual measurement control measured by the timer 350 is equal to or greater than a predetermined period of time.

[0065] If the execution condition is not satisfied (S702: N), the first CPU 311 waits until the execution condition is satisfied. If the execution condition is satisfied (S702: Y), the first CPU 311 forms a pattern image on the intermediate transfer body 252 by the image forming engine 101 (S703). The pattern image includes a patch image of a gradation (image density) based on the γLUT 506 notified to the image forming engine 101 in the process of S701.

[0066] The first CPU 311 acquires image density data, which is the result of the image density sensor 230 reading the pattern image on the intermediate transfer body 252, from the patch reading unit 502 of the image forming engine 101 (S704). The first CPU 311 performs a correction calculation to generate a γLUT to be updated using the image density data acquired from the image forming engine 101, the actual measurement control target 504 stored in the RAM 307, and the γLUT 506 by the tone correction table generating unit 306 (S705). The details of the method of calculating the γLUT are a known technique, so a detailed description will be omitted here.

[0067] The first CPU 311 updates the γLUT 506 with the new γLUT generated in the process of S705 by the tone correction table generation unit 306 (S706). The γLUT 506 is a γLUT used during actual measurement control. The first CPU 311 updates the γLUT 503 with the new γLUT generated in the process of S705 by the tone correction table generation unit 306 (S707). The γLUT 503 is a γLUT used when printing in accordance with a print job. As a result, the contents of the γLUT 506 and the γLUT 503 become the same.

[0068] The first CPU 311 updates the predicted reference density 505 in the RAM 307 using the image density data acquired in the process of S704 as the predicted reference density (S708). The first CPU 311 notifies the image forming engine 101 of the value extracted from the γLUT 506 corresponding to the pattern image formed in the actual measurement control (S709). This ends the actual measurement control. Both the γLUT 503 and the γLUT 506 are updated by the actual measurement control. At the next actual measurement control, the value of the γLUT 506 notified in the process of S709 is used.

[0069] Fig. 9 is a flow chart showing automatic tone correction and actual measurement control, which is tone correction using sheet S. In this process, the actual measurement control target 504 is updated. Since the details of automatic tone correction are a known technique, a detailed description will be omitted here. Fig. 9(a) shows the overall flow of this process.

[0070] The first CPU 311 acquires an instruction to execute automatic tone correction from the operation panel 191 (S801). The first CPU 311 prints a predetermined pattern image used for the automatic tone correction on the sheet S by the image forming engine 101 (S802). At this time, the first CPU 311 performs predetermined image processing on the image data of the predetermined pattern image used for the automatic tone correction by the color processing unit 313, the tone correction unit 314, and the pseudo halftone processing unit 315. The image forming engine 101 performs printing processing based on the image data after the image processing. The sheet S on which the predetermined pattern image used for the automatic tone correction is printed is placed on the document tray 400 or the document glass 412 by the user. The predetermined pattern image is, for example, the pattern image shown in FIG. 4.

[0071] The first CPU 311 reads the pattern image of the sheet S placed on the document tray 400 or the document glass 412 by the scanner 171 in response to an instruction from the operation panel 191 (S803). If the image forming apparatus 100 is configured to have a colorimetric sensor inside, the sheet S on which a predetermined pattern image is printed is read by the colorimetric sensor. The colorimetric sensor is provided, for example, on the conveying path of the sheet S downstream of the fixing device 260 in the conveying direction until the sheet S is discharged outside the apparatus.

[0072] The first CPU 311 analyzes the result of reading the pattern image by the scanner 171 (read image) and performs a correction calculation to generate a γLUT to be updated (S804). The first CPU 311 updates the γLUT 506 with the new γLUT generated in the processing of S804 (S805). The γLUT 506 is a γLUT used during actual measurement control. The first CPU 311 updates the γLUT 503 with the new γLUT generated in the processing of S804 (S806). The γLUT 503 is a γLUT used when printing according to a print job.

[0073] After updating the γLUTs 506 and 503, the first CPU 311 performs processing to update the actual measurement control target 504 referred to by the tone correction table generating unit 306 (S807). Fig. 9B shows the processing to update the actual measurement control target 504 in S807.

[0074] The first CPU 311 notifies the image forming engine 101 of the value extracted from the γLUT 506 to be used for the pattern image (patch image) output by actual measurement control (S808). The image forming engine 101 stores the notified data in a memory (not shown). The first CPU 311 causes the image forming engine 101 to form a pattern image on the intermediate transfer body 252 based on the γLUT 506 (S809).

[0075] The first CPU 311 acquires image density data, which is the result of the image density sensor 230 reading the pattern image on the intermediate transfer body 252, from the patch reading unit 502 of the image forming engine 101 (S810). The first CPU 311 generates an actual measurement control target based on the acquired image density data (S811). For example, when the pattern image includes 10 patch images, the first CPU 311 expands the image density values ​​of the 10 patch images by linearly interpolating them. As a result, an actual measurement control target including, for example, 1024 image density values ​​is generated.

[0076] The first CPU 311 updates the actual control target 504 with the new actual control target generated in the process of S811 (S812). The first CPU 311 updates the predicted reference density 505 with the image density data acquired in the process of S810 (S813).

[0077] Through the above processing, the γLUT 503, the γLUT 506, the actual measurement control target 504, and the predicted reference density 505 are updated during automatic tone correction. At the next actual measurement control, the value of the γLUT 506 is notified to the image forming engine 101.

[0078] FIG. 10 is a flowchart showing the predictive control.

[0079] The first CPU 311 determines whether the conditions for executing predictive control are satisfied by the image forming engine 101 (S901). The conditions for executing predictive control are, for example, the number of sheets printed since the previous predictive control, a predetermined time interval, and start-up. The number of sheets printed is counted by the counter 360, and if the count value is equal to or greater than a predetermined number, it is determined that the conditions for execution are satisfied. The time interval is measured by the timer 350 and is the elapsed time since the previous predictive control.

[0080] If the execution condition is not satisfied (S901: N), the first CPU 311 waits until the execution condition is satisfied. If the execution condition is satisfied (S901: Y), the first CPU 311 acquires prediction elements necessary for predictive control from the image forming engine 101 (S902). The input data necessary for predictive control is, for example, at least one of the detection result of the sensor 340, the time by the timer 350, the count value by the counter 360, and the image forming condition by the image forming condition generating unit 370.

[0081] The first CPU 311 determines the amount of density change related to the change in density over time based on the input data acquired in the process of S902 through the predicted density calculation unit 305, and predicts the image density value of the pattern image if the pattern image is formed on the sheet S (S903). In the process of S903, the predicted density calculation unit 305 sums the amount of density change and the predicted reference density 505 to determine the image density value of the pattern image. The first CPU 311 performs a correction calculation using the image density value predicted in the process of S903 and the γLUT 503 through the gradation correction table generation unit 306 to generate a γLUT to be updated (S904). The first CPU 311 updates the γLUT 503 with the new γLUT generated in the process of S904 through the gradation correction table generation unit 306 (S905). The γLUT 503 is a γLUT used when printing according to a print job. In the predictive control, the predicted density calculation unit 305 and the gradation correction table generation unit 306 function as an update unit that determines the amount of density change related to the change in density over time and updates the image formation conditions based on the amount of density change.

[0082] As described above, the image forming apparatus 100 of this embodiment includes the γLUT 506 for actual measurement control and the γLUT 503 used for printing. The γLUT 506 is not updated by predictive control. With this configuration, the γLUT 503 can be updated frequently by predictive control, and actual measurement control can be performed with high accuracy by the γLUT 506 even when an optimal γLUT 503 cannot be generated by predictive control. Therefore, calibration performed by forming an image can be stably performed with high accuracy without being affected by calibration based on prediction.

[0083] In the above embodiment, the correction of the γLUT for tone correction has been described. The γLUT is one of the image forming conditions when the image forming apparatus 100 forms an image. This embodiment can also be applied to image forming conditions other than the γLUT. That is, this embodiment can be applied to the image forming apparatus 100 that performs actual measurement control for correcting the image forming conditions based on the result of reading a pattern image and predictive control for correcting the image forming conditions based on predictive factors such as environmental conditions and the state of components. In addition to the γLUT, such image forming conditions include, for example, a set value of image density, a correction value for geometric characteristics such as the print position and shape of an image, a correction value for color misregistration, a voltage value during charging, conditions during development, and a voltage value during transfer.

[0084] In addition, in the above-described embodiment, the amount of density change is determined based on the input data as data regarding the change in density over time. However, the data may be determined based on the input data as the result of reading the pattern image by the image density sensor 230.

Claims

1. An image forming apparatus for forming an image on a sheet, an image forming means for forming an image based on image forming conditions; an image carrier on which a pattern image is formed by the image forming means; a reading means for reading the pattern image on the image carrier; a generating means for generating the image forming conditions based on a result of reading the pattern image by the reading means; and an updating means for determining data relating to a change in image density over time and updating the image forming conditions based on the data; the image forming means forms the pattern image based on the image forming conditions generated by the generating means before the update by the updating means when a condition for forming a pattern image is satisfied after the image forming conditions are updated by the updating means. Image forming device.

2. The update unit determines the data based on a change in an environmental condition of the image forming apparatus.

2. The image forming apparatus according to claim 1.

3. The update means determines the data based on the status of components of the image forming apparatus.

2. The image forming apparatus according to claim 1.

4. the image forming unit performs image formation by a print job based on the image forming conditions before the update by the update unit.

2. The image forming apparatus according to claim 1.

5. The update of the image forming conditions by the update means is performed more frequently than the generation of the image forming conditions by the generation means.

2. The image forming apparatus according to claim 1.

6. a transfer means for transferring the image formed on the image carrier onto a sheet; a fixing means for fixing the image transferred onto the sheet; A second reading means capable of reading an image formed on the sheet; and a second update unit that updates the image forming conditions generated by the generation unit and the image forming conditions updated by the update unit using image forming conditions generated based on a reading result by the second reading unit of the sheet on which the pattern image is formed.

2. The image forming apparatus according to claim 1.

7. the generating means generates a target value of the image forming condition from a reading result of the pattern image formed on the image carrier by the reading means based on the image forming condition updated by the second updating means.

7. The image forming apparatus according to claim 6.

8. the update means generates a reference value of the data from a reading result of the pattern image formed on the image carrier by the reading means based on the image forming conditions updated by the second update means, 7. The image forming apparatus according to claim 6.

Images