JP7146380B2 - image forming device - Google Patents

Description

The present invention relates to density prediction control for predicting the density of an output image.

In an image forming apparatus using electrophotographic technology, there is a possibility that the density of the output image may not reach the target density due to changes in the environment in which the apparatus is installed, deterioration of each member, and the like. Therefore, in order to control the density of the output image to the target density, the image forming apparatus forms a measurement image and corrects the image forming conditions based on the measurement result of the measurement image.

However, if the image forming apparatus interrupts the formation of the output image and forms the image for measurement, the productivity decreases. Accordingly, some recent image forming apparatuses correct the density of an output image based on a detection value of a sensor provided in the image forming apparatus (Patent Document 1). In such an image forming apparatus, a model formula is designed in advance, and image forming conditions are corrected based on the model formula based on sensor detection values.

JP 2010-102317 A

However, in the image forming apparatus described in Patent Document 1, when a large number of images are formed or when the amount of developer consumed is extremely small or excessively large, there is a possibility that the prediction accuracy of the density prediction control is lowered. .

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to prevent the accuracy of predicting the density of an output image from deteriorating.

In order to solve the above-described problems, an image forming apparatus of the present invention has a developer containing developer containing toner and carrier, and uses the developer in the developer to form an image on a sheet. forming means , storage means, a sensor for detecting the toner density of the developer in the developing device, an image carrier for carrying an image for measurement formed by the image forming means, and the image carrier. measuring means for measuring the measurement image on the body; forming a pattern image on a sheet by the image forming means; reading data relating to the pattern image output from a reading device; a first generating means for generating image forming conditions for controlling the density of an image based on the read data; and a first measurement for the image forming means based on the image forming conditions generated by the first generating means. control means for forming an image for measurement, causing the measurement means to measure the first image for measurement, and storing the measurement result of the first image for measurement by the measurement means as a reference density in the storage means; determining an amount of density variation from the image forming means based on the detection result of the sensor, determining a predicted density of an image formed by the image forming means based on the reference density and the density variation amount stored in the storage means; a second generation unit for generating the image forming conditions based on the predicted density; and causing the measurement means to measure the second image for measurement, and correcting the reference density based on the result of measurement of the second image for measurement by the measurement means. do.

According to the present invention, it is possible to suppress deterioration in prediction accuracy of concentration prediction control.

Schematic cross-sectional view of an image forming apparatus Control block diagram of image forming apparatus Functional Block Diagram of Predicted Concentration Calculator Flowchart of automatic gradation correction Schematic diagram of pattern image 1 Schematic diagram of pattern image 2 Explanatory diagram of the generation method of the gradation correction table Schematic diagram of a patch image formed on an intermediate transfer belt Flowchart of prediction correction LUT creation processing FIG. 4 is a diagram showing the correspondence relationship between image signal values and density fluctuation amounts; Diagram showing density characteristics (gradation characteristics) A diagram showing an initial correction LUT and a prediction correction LUT Flowchart of update processing of reference density and basic signal value Table showing an example of model coefficients Schematic diagram of UI screen

FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100. As shown in FIG. The image forming apparatus 100 includes a reader A, printer 101 and operation panel 20 . Further, the image forming apparatus 100 also includes a printer controller 300 (FIG. 2) and an image processing section 110 (FIG. 2).

The printer 101 forms an image on the sheet P. FIG. The printer 101 includes image forming units PY, PM, PC, and PK that form images of different colors, and a fixing device 11 that fixes the images on the sheet P. FIG. The printer 101 of this embodiment further includes a CPU 120 ( FIG. 2 ) for controlling the image forming units PY, PM, PC, and PK, and the fixing device 11 .

The image forming station PY forms a yellow image, the image forming station PY forms a magenta image, the image forming station PC forms a cyan image, and the image forming station PK forms a black image. The image forming units PY, PM, PC, and PK have substantially the same configuration, except that the toner colors contained in the developing units 4Y, 4M, 4C, and 4K are different from yellow, magenta, cyan, and black. In the following description, the suffixes Y, M, C, and K will be omitted unless otherwise specified.

The photosensitive drum 1 is a photosensitive member in which a photosensitive layer (photosensitive member) is formed on the outer peripheral surface of an aluminum cylinder. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 at a predetermined speed. The charger 2 is a scorotron charger that charges the surface of the photosensitive drum 1 to a uniform negative potential. In the charger 2, a charging voltage is applied to a wire from a power supply unit (not shown), and a grid bias is applied to a grid member of the power supply unit (not shown).

The exposure unit 3 exposes the charged surface of the photosensitive drum 1 . Thereby, an electrostatic latent image is formed on the surface of the photosensitive drum 1 . The developing device 4 accumulates developer containing toner and carrier. The exposure unit 3 is, for example, a laser scanner including a light source and a rotating polygonal mirror, or a laser scanner in which a plurality of LEDs are arranged in a line.

The developing device 4 includes a developing sleeve that carries a developer and supplies the toner to the photosensitive drum 1, a rotating member that rotates to agitate the developer accumulated in the developing device 4, and a developer that is supplied to the developing device. Equipped with a replenishment mechanism. A developing bias is supplied to the developing sleeve from a power supply unit (not shown). The developing device 4 causes the developer carried on the developing sleeve to adhere to the photosensitive drum 1 due to the potential difference between the developing sleeve and the photosensitive drum 1 . Thereby, the electrostatic latent image formed on the photosensitive drum 1 is visualized. The developing device 4 also includes an inductance sensor 200 that detects the toner density of the developer accumulated in the developing device 4 . Here, the toner concentration is a parameter indicating the ratio of the amount of toner to the amount of developer. The replenishment mechanism has a replenishment screw that rotates to replenish the developer.

The intermediate transfer belt 6 is a belt looped around a drive roller 61 , a tension roller 62 and a roller 63 . The intermediate transfer belt 6 moves in the direction of arrow R2 as the drive roller 61 rotates. Also, the primary transfer roller 7 presses the intermediate transfer belt 6 to form a primary transfer portion T1 between the photosensitive drum 1 and the intermediate transfer belt 6 . When a transfer voltage is applied to the primary transfer roller 7, the toner image carried on the photosensitive drum 1 is transferred to the intermediate transfer belt 6 at the primary transfer portion T1. This is called primary transfer. Further, the cleaning device 68 has a cleaning blade that rubs the intermediate transfer belt 6 and cleans the toner remaining on the intermediate transfer belt 6 without being transferred from the intermediate transfer belt 6 to the recording material P. FIG.

The secondary transfer roller 64 is arranged on the side opposite to the roller 63 with respect to the intermediate transfer belt 6 . The secondary transfer roller 64 forms a secondary transfer portion T<b>2 between the secondary transfer roller 64 and the intermediate transfer belt 6 . The toner image carried on the intermediate transfer belt 6 is transferred onto the recording material P by applying a transfer voltage to the secondary transfer roller 64 . This is called secondary transcription.

The image density sensor 400 measures the image for measurement carried on the intermediate transfer belt 6 . The image density sensor 400 is, for example, an optical sensor that has a light-emitting element and a light-receiving element and measures reflected light from the measurement image. The intensity or amount of reflected light from the image for measurement changes according to the toner adhesion amount of the image for measurement. The image forming apparatus 100 can detect the density of the measurement image based on, for example, a conversion table between the intensity of the reflected light from the measurement image and the density of the measurement image.

The sheet cassette 65 accommodates sheets P. As shown in FIG. An environment sensor 199 is arranged around the sheet cassette 65 . The environmental sensor 199 senses environmental information. Environmental information is, for example, humidity (relative humidity). Environmental information is not limited to relative humidity, and may be temperature or both temperature and relative humidity. Alternatively, the environmental information may be absolute humidity.

The feeding roller 66 separates the sheets P one by one from the sheet cassette 65 and conveys the sheets P. As shown in FIG. The registration rollers 67 adjust the delivery timing of the sheet P while transporting the sheet P in order to control the timing at which the sheet P transported by the feeding roller 66 reaches the secondary transfer portion T2.

The fixing device 11 has a roller pair and a heater. The fixing device 11 heats the sheet P with a heater while the sheet P is passing through the nip portion of the roller pair. As a result, the toner image on the sheet P is melted and fixed on the sheet. The sheet P that has passed through the fixing device 11 is discharged to the discharge tray 109 . The feeding roller 66, the registration roller 67, and the fixing device 11 form a conveying path for conveying the sheet.

The reader A has a platen 102 , a light source 103 , a lens 104 , a mirror 105 and a CCD sensor 108 . The light source 103, lens 104, and mirror 105 constitute a carriage that moves in a predetermined direction.

The reading operation of the document G will be described below. A user places a document G on the document platen 102 and inputs a reading instruction from the operation panel 20 . When a reading instruction is input, the carriage moves in a predetermined direction while the light source 103 emits light. Reflected light from the document G forms an image on the CCD sensor 108 via the lens 104 and mirror 105 . Then, the CCD sensor 108 transfers the read data of the document G to the printer controller 300 (FIG. 2). The same applies to the reading operation of the test chart.

The operation panel 20 has a liquid crystal display 218 . The user can input print information such as the number of images to be printed and designation of single-sided printing or double-sided printing via the operation panel 20 . The printer 101 performs image forming processing based on print information input from the operation panel unit 20 . Also, the user can control the reader A via the operation panel 20 . Also, the user can calibrate the printer B through the operation panel 20 .

Next, image forming processing in which the printer 101 forms an image on the sheet P will be described.

The image forming units PY, PM, PC, and PK sequentially form images based on image data. Then, the primary transfer rollers 7Y, 7M, 7C, and 7K transfer the toner images formed by the image forming units PY, PM, PC, and PK so as to overlap on the intermediate transfer belt 6. FIG. Thereby, a full-color toner image is formed on the intermediate transfer belt 6 .

On the other hand, the feeding roller 66 conveys the sheet P accommodated in the sheet cassette 65 toward the registration roller 67 . The registration roller 67 conveys the sheet P so that the toner image formed on the intermediate transfer belt 6 reaches the secondary transfer portion T2 at the same timing as the sheet P reaches the secondary transfer portion T2. Then, the secondary transfer roller 64 transfers the toner image on the intermediate transfer belt 6 onto the sheet P. As shown in FIG. A conveying roller (not shown) conveys the sheet P onto which the toner image has been transferred to the fixing device 11 . When the sheet P passes through the fixing device 11, the fixing device 11 fixes the toner image transferred to the sheet P by heat and pressure. Then, the sheet P on which the toner image is fixed is discharged to the discharge tray 109 .

FIG. 2 is a control block diagram of the image forming apparatus 100. As shown in FIG. The image forming apparatus 100 includes a printer controller 300 , a program ROM 304 , a RAM 309 and an image processing section 110 . A CPU 313 of the printer controller 300 is a processor that comprehensively controls the image forming apparatus 100 . The program ROM 304 stores various control programs and control data executed by the CPU 313 . A RAM 309 is a system work memory. The image processing unit 110 is an ASIC (Application Specific Integrated Circuit) for executing image processing on image data.

The image processing unit 110 has a RIP (Raster Image Processor) 314 , a color processing unit 315 , a tone correction unit 316 and a halftone processing unit 317 . The RIP 314 converts image data into bitmap format image data. A color processing unit 315 converts the color information of the input image data into color information suitable for the printer 101 . The color processing unit 315 converts, for example, red, green, and blue image data into yellow, magenta, cyan, and black image data.

A gradation correction unit 316 converts image signal values included in image data in order to correct the gradation characteristics (also called density characteristics) of an image formed by the printer 101 to ideal gradation characteristics. The gradation correction unit 316 converts the image signal values included in the image data by referring to, for example, a gradation correction table (γLUT) indicating the correspondence between the input image signal values and the output image signal values. . The gradation correction table is gradation correction conditions for correcting the gradation characteristics of an output image to ideal gradation characteristics. A tone correction table (γLUT) is a one-dimensional conversion table. A tone correction table (γLUT) is stored in a memory (not shown) for each color. Note that the gradation correction unit 316 is not limited to the gradation correction table, and may be configured to convert the image signal value based on, for example, a conversion formula. A halftone processing unit 317 dithers image data to generate image data to be input to the printer 101 .

The printer 101 includes image forming units PY, PM, PC, and PK, and a fixing device 11 . A CPU 120 is a processor that controls the image forming units PY, PM, PC, and PK and the fixing device 11 . The CPU 120 controls the printer 101 according to print commands input from the CPU 313 . The printer 101 forms an image based on image data transferred from reader A, or forms an image based on image data transferred from a server or PC (not shown). Further, the printer 101 forms a patch image (FIG. 8) based on the image data for measurement (image signal value for measurement), or prints the pattern image data (pattern image signal value) in order to control image forming conditions, which will be described later. A pattern image (FIGS. 5 and 6) is formed based on . A patch image is a measurement image that is measured by the image density sensor 400 . On the other hand, the pattern image is an image for measurement formed on the sheet P. FIG.

The printer controller 300 has a maximum density condition determination unit 306 , a predicted density calculation unit 307 and a gradation correction table generation unit 308 . A maximum density condition determination unit 306 determines image forming conditions for adjusting the maximum density of an image formed by the printer 101 . An image forming condition for adjusting the maximum density of an image formed by the printer 101 is, for example, the intensity of light (exposure intensity) with which the exposure unit 3 exposes the photosensitive drum 1 .

The image forming conditions for adjusting the maximum density may be the charging voltage or the grid bias for charging the photosensitive drum 1 by the charger 2 . Alternatively, the image forming condition for adjusting the maximum density may be the developing bias applied to the developing sleeve of the developing device 4 .

The predicted density calculator 307 will be described later with reference to FIG. A gradation correction table generation unit 308 generates image forming conditions for adjusting the gradation characteristics of an image formed by the printer 101 to ideal gradation characteristics. Image forming conditions for adjusting the gradation characteristics of an image formed by the printer 101 to ideal gradation characteristics are a gradation correction table (γLUT) for converting image signal values of image data.

Since the reader A, the environment sensor 199, the inductance sensor 200, and the operation panel 20 have been described with reference to FIG. 1, their description will be omitted here. A timer 201 measures the time during which each unit of the printer 101 is driven. The timer 201 measures, for example, the idle time during which the printer 101 does not form an image. Here, the standing time may be, for example, the time during which the developing screw of the developing device 4 is not rotating. A counter 202 measures the number of revolutions of the supply screw of the supply mechanism. The number of rotations of the replenishment screw corresponds to the number of replenishments. The amount of toner supplied to the developing device 4 by one rotation of the supply screw is predetermined. In other words, it can be said that the counter 202 measures the amount of toner supplied to the developing device 4 . Alternatively, the counter 202 may be configured to measure the number of rotations of the rotating member. The toner accumulated in the developing device 4 is triboelectrically charged according to the number of rotations of the rotating member. In other words, the number of rotations of the rotating member is a parameter for predicting the charge amount of the toner.

The printer controller 300 of this embodiment has a predicted density calculator 307 that predicts the density of an output image formed by the printer 101 . The predicted density calculator 307 of the present embodiment predicts the amount of density variation from the reference density based on the detected value of the environment sensor 199 and the detected value of the inductance sensor 200, and obtains the predicted density of the output image. Then, the tone correction table generation unit 308 adjusts the tone correction table based on the density predicted by the predicted density calculation unit 307 (predicted density).

The printer controller 300 controls the image forming conditions based on the density predicted by the predicted density calculator 307 without forming the measurement image. In other words, the printer controller 300 of the present embodiment predicts the density of the output image and controls the image forming conditions without forming the measurement image when the main power supply of the image forming apparatus 100 is turned on. Downtime until the image is formed can be shortened. Further, the printer controller 300 of the present embodiment can similarly shorten the downtime until an output image is formed even when the image forming apparatus 100 shifts from the sleep mode to the standby mode.

FIG. 3 is a control block diagram showing details of the predicted density calculator 307 shown in FIG. The predicted concentration calculator 307 obtains the difference between the detected value obtained from the environment sensor 199 and the inductance sensor 200 and the reference detected value, and calculates the concentration fluctuation amount from the difference based on a model formula stored in advance. . Then, the predicted density calculation unit 307 predicts the density of the output image based on the pre-stored reference density and density fluctuation amount.

The predicted density calculation section 307 includes an input signal value processing section 320 having a signal value storage section 321 and a difference calculation section 322 and a density prediction section 330 having a density storage section 331 and a prediction section 332 . Input signal value processing unit 320 receives detection values output from each of environment sensor 199 and inductance sensor 200 . Signal value storage unit 321 stores the reference detection value of environment sensor 199 and the reference detection value of inductance sensor 200 . Difference calculator 322 calculates the difference between the detection value of environment sensor 199 and the reference detection value of environment sensor 199 . A density storage unit 331 stores a reference density. The prediction unit 332 calculates the amount of density variation with respect to the reference density based on the image density prediction model formula, and predicts the density of the output image based on the reference density and the amount of density variation stored in the density storage unit 331 .

Here, the predicted density calculation unit 307 of the present embodiment obtains predicted densities corresponding to ten image signal values, for example. The ten image signal values are, for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%. This is because, for example, the amount of change in density of an image formed based on an image signal value of 10% differs from the amount of change in density of an image formed based on an image signal value of 90%. The predicted density calculation unit 307 can predict the gradation characteristics of the image forming apparatus 100 by obtaining a plurality of predicted densities. Therefore, the predicted density calculation unit 307 of this embodiment requires ten image density prediction model formulas. A tone correction table generation unit 308 corrects the tone correction table (γLUT) based on the ten predicted densities calculated by the predicted density calculation unit 307 . A method for correcting the gradation correction table (γLUT) from the predicted density will be described later with reference to FIGS. 9 to 12. FIG.

In addition, the model formula of the present embodiment has two input values: a value obtained by multiplying the detection value (toner concentration) of the inductance sensor 200 by a coefficient, and a value obtained by multiplying the detection value (environmental humidity) of the environment sensor 199 by a coefficient. and FIG. 14 exemplifies the coefficients for each image signal value.

Next, a method of obtaining the reference detection value stored in the signal value storage unit 321 and the reference density stored in the density storage unit 331 will be described. The printer controller 300 acquires a reference detection value and a reference density when automatic tone correction is executed. Automatic gradation correction is calibration in which a pattern image is formed on the sheet P using the printer 101 and image forming conditions are corrected based on the result of reading the pattern image by the reader A. FIG. The automatic tone correction performed by the image forming apparatus 100 will be described below with reference to FIGS. 4 to 7. FIG.

FIG. 4 is a flowchart of automatic gradation correction. For example, when the user inputs an automatic tone correction execution command from the operation panel 20 , the CPU 313 executes the automatic tone correction control program stored in the program ROM 304 .

When the automatic gradation correction is executed, the CPU 313 controls the printer 101 to form the pattern image 1 on the sheet P (S201). The CPU 313 transfers pattern image data corresponding to the pattern image 1 to the CPU 120 . The CPU 120 forms the pattern image 1 on the sheet P by controlling the printer 101 based on the pattern image data corresponding to the pattern image 1 . A schematic diagram of the pattern image 1 is shown in FIG. Pattern image 1 includes 10 pattern images for each color. The pattern image 1 includes, for example, ten pattern images having different intensities of light (exposure intensity) with which the exposure unit 3 exposes the photosensitive drum 1 . Hereinafter, the exposure intensity of the exposure unit 3 will be referred to as LPW.

The CPU 313 reads the pattern image 1 (S202). The user places the sheet P on which the pattern image 1 is formed and output to the discharge tray 109 on the document platen 102 and presses the read button on the operation panel 20 . Reader A executes a reading operation and transfers the read data of pattern image 1 to CPU 313 . Thereby, the CPU 313 acquires the read data of the pattern image 1 output from the reader A. FIG.

CPU 313 determines the LPW based on the read data of pattern image 1 (S203). In step S203, the maximum density condition determination unit 306 obtains the density of each pattern image 1 from the read data, linearly interpolates the density of the pattern image 1 for each color to obtain the correspondence relationship between the density and the LPW, and obtains the target density. Determine the corresponding LPW. A maximum density condition determination unit 306 determines an LPW for each color to form an image with a target density.

Next, the CPU 313 controls the printer 101 to form the pattern image 2 on the sheet P (S204). CPU 313 transfers pattern image data corresponding to pattern image 2 to CPU 120 . The CPU 120 forms the pattern image 2 on the sheet P by controlling the printer 101 based on pattern image data corresponding to the pattern image 2 . At this time, the CPU 120 controls the image forming conditions of the printer 101 based on the LPW determined in step S203. A schematic diagram of the pattern image 2 is shown in FIG. The pattern image 2 includes pattern images of 64 gradations for each color. That is, the pattern image data corresponding to pattern image 2 includes 64 image signal values for each color. At this time, the charging voltage, grid bias, LPW, and developing bias are not changed. Pattern image 2 includes image signal values of patch image 1 and patch image 2, which will be described later.

The CPU 313 reads the pattern image 2 (S205). The user places the sheet P on which the pattern image 2 is formed and output to the discharge tray 109 on the document platen 102 and presses the read button on the operation panel 20 . Reader A executes the reading operation and transfers the read data of pattern image 2 to CPU 313 . Thereby, the CPU 313 acquires the read data of the pattern image 2 output from the reader A. FIG.

The CPU 313 generates a gradation correction table (initial correction LUT) based on the read data of pattern image 2 (S206). In step S206, the gradation correction table generation unit 308 obtains the density of each pattern image 2 from the read data, linearly interpolates the density of the pattern image 2 for each color, and acquires the gradation characteristics of the printer 101. FIG. Then, the gradation correction table generation unit 308 generates image signal values so that the gradation characteristics (engine γ characteristics) of the printer 101 become ideal gradation characteristics (gradation target), as shown in FIG. Generate an initial correction LUT for the transform. Thereby, the density of the image formed on the sheet P by the printer 101 is controlled to the target density.

Next, the CPU 313 acquires the reference density and the reference signal value. CPU 313 controls printer 101 to form patch image 1 (S207). That is, the printer 101 continuously forms the pattern image 2 and the patch image 1 . CPU 313 transfers measurement image data corresponding to patch image 1 to CPU 120 . The CPU 120 controls the printer 101 based on the measurement image data corresponding to the patch image 1 to form the patch image 1 on the intermediate transfer belt 6 . At this time, the CPU 120 controls the image forming conditions of the printer 101 based on the LPW determined in step S203. A schematic diagram of the patch image 1 is shown in FIG. The patch image 1 includes, for example, patch images with 10 gradations for each color. Image signal values for forming patch image 1 are, for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%. At this time, the charging voltage, grid bias, LPW, and development bias are not changed.

The CPU 313 measures the patch image 1 with the image density sensor 400 (S208). In step S208, the CPU 313 obtains the density of the patch image 1 from the measurement result of the image density sensor 400, and stores the density of the patch image 1 in the density storage unit 331 as the reference density. The density storage unit 331 stores reference densities corresponding to ten image signal values. Since the image density prediction model formula of the present embodiment is a formula for determining the density fluctuation amount of the patch density on the intermediate transfer belt 6, the density of the patch image on the intermediate transfer belt 6 is used as the reference density. However, for example, when using a model formula for predicting the amount of density variation in the patch density on the sheet P, the printer 101 forms the patch image 1 on the sheet P and uses the density of the patch density on the sheet P as the reference density. Just memorize it.

When the CPU 313 executes the automatic gradation correction, the CPU 313 stores the detection value output from the environment sensor 199 and the detection value output from the inductance sensor 200 as reference detection values in the signal value storage unit 321 (S209). As a result, the reference density and the reference detection value are acquired. Then, the CPU 313 ends the automatic gradation correction process.

After the automatic gradation correction is executed and the initial correction LUT is generated, the density of the output image is controlled to the target density for a while. However, the density of the output image changes due to changes in elapsed time and environment (temperature and humidity). In particular, when forming an image after the image forming apparatus 100 has been left for a while, there is a high possibility that the density of the output image will deviate from the target density.

Therefore, in the image forming apparatus 100 of the present embodiment, the predicted density calculation unit 307 predicts the density fluctuation amount of the output image, and corrects the gradation correction table so that the density of the output image becomes the target density. A method of correcting the gradation correction table (γLUT) from the predicted density will be described below with reference to FIGS. 9 to 12. FIG.

FIG. 9 is a flow chart of processing for creating a prediction correction LUT for correcting an output image to a target density without forming an image for measurement. For example, when forming an image immediately after the main power supply of the image forming apparatus 100 is turned on, the CPU 313 executes a control program for creating a prediction correction LUT stored in the program ROM 304 .

When the process of creating the prediction correction LUT is executed, the CPU 313 acquires the detection value of the environment sensor 199 and the detection value of the inductance sensor 200 (S101). Next, the difference calculation unit 322 calculates the difference between the reference signal value stored in the signal value storage unit 321 and the detection value acquired in step S101 (S102). In step S102, the difference calculator 322 calculates the difference between the reference detection value of the environment sensor 199 and the detection value of the environment sensor 199, and the difference between the reference detection value of the inductance sensor 200 and the detection value of the inductance sensor 200. .

The prediction unit 332 predicts the density fluctuation amount based on the image density prediction model formula from the difference calculated in step S102 (S103). In step S103, the prediction unit 332 predicts density fluctuation amounts corresponding to ten image signal values. FIG. 10 is a diagram showing the correspondence relationship between the image signal values obtained by linearly interpolating the density fluctuation amount and the density fluctuation amount. In the following description, it is assumed that the concentration has decreased. The density prediction unit 330 adds the density fluctuation amount predicted by the prediction unit 332 and the reference density stored in the density storage unit 331 to calculate a predicted density, and creates a predicted density characteristic (S104). FIG. 11 is a diagram comparing density characteristics of reference densities (reference density characteristics) and density characteristics of predicted densities (predicted density characteristics). The predicted concentrations are generally lower than the reference concentrations.

Then, the gradation correction table generation unit 308 generates a prediction correction LUT so that the predicted density characteristics created in step S104 become target density characteristics (ideal gradation characteristics) (S105). In step S105, the method for generating the prediction correction LUT is the same as the method for generating the initial correction LUT. FIG. 12 is a diagram showing an initial correction LUT and a prediction correction LUT. Since the predicted density has decreased with respect to the reference density, the predicted correction LUT is a conversion table in which the output signal value is larger than that of the initial correction LUT. Then, the CPU 313 ends the process of generating the prediction correction LUT.

Next, the necessity of correcting the basic density will be explained.

According to the inventor's experiment, when a large number of images were formed, the predicted density value was lower than the actual density value. This is considered to be caused by deterioration of the developer accumulated in the developing device 4, for example. Furthermore, according to experiments conducted by the inventors, it was found that even when a large number of images were formed, the absolute value of the density changed, but the transition of the variation amount of the density did not change. Therefore, the image forming apparatus 100 of the present embodiment updates the reference density and the reference detection value, for example, when 10,000 pages of images have been formed since the previous setting of the reference density.

An update process for updating the reference density and the reference detection value will be described below with reference to FIG. Note that in the update process shown in FIG. 13, the image for measurement is not formed on the sheet P, so wasteful consumption of the sheet P can be suppressed, and furthermore, the user does not have to have the reader A read the sheet P. The CPU 313 executes the update processing control program stored in the program ROM 304 while the main power supply of the image forming apparatus is ON.

First, the CPU 313 determines whether or not the number of one-page images formed by the printer 101 (the number of images formed) after the reference density was stored in the density storage unit 331 last time has reached a predetermined number (S501). . In step S501, the predetermined number is, for example, 10,000 pages. If the number of sheets to be formed with images is less than the predetermined number in step S501, the CPU 313 terminates this process.

When the number of images to be formed reaches the predetermined number, the CPU 313 controls the printer 101 to form patch image 2 (S502). In step S<b>502 , the CPU 313 transfers measurement image data corresponding to the patch image 2 to the CPU 120 . Assume that the measurement image data corresponding to the patch image 2 in this embodiment is the same as the measurement image data corresponding to the patch image 1 described above. The CPU 120 controls the printer 101 based on the measurement image data corresponding to the patch image 2 to form the patch image 2 on the intermediate transfer belt 6 . At this time, the CPU 120 controls the image forming conditions of the printer 101 based on the LPW determined by the automatic gradation correction.

The CPU 313 measures the patch image 2 with the image density sensor 400 (S503). In step S503, the CPU 313 obtains the density of the patch image 2 from the measurement result of the image density sensor 400. FIG. Then, the CPU 313 stores the density of the patch image 2 as the reference density in the density storage unit 331 (S504). As a result, the reference densities corresponding to the ten image signal values stored in the density storage unit 331 are updated. Further, the CPU 313 stores the detection value output from the environment sensor 199 and the detection value output from the inductance sensor 200 as reference detection values in the signal value storage unit 321 (S505). Thereby, the reference detection value stored in the signal value storage unit 321 is updated.

After the reference density and the reference signal value are updated in steps S504 and S505, the CPU 313 sets the value of the number of image formation sheets to 0, and terminates the update process. Similarly, the CPU 313 sets the value of the number of images to be formed to 0 when the automatic gradation correction is executed. In other words, the CPU 313 updates the reference density when the number of images formed reaches the predetermined number without updating the reference density. Similarly, the CPU 313 updates the reference signal value when the number of images formed reaches a predetermined number without updating the reference signal value.

Further, although the CPU 313 of the present embodiment is configured to execute the update process when the number of image formation sheets reaches the predetermined number, the timing at which the update process is executed is not limited to this configuration. For example, the CPU 313 may execute the update process when the cumulative value of the image ratio (image ratio) for the sheet P obtained by analyzing the image data exceeds a predetermined value. Alternatively, CPU 313 may execute the update process each time the time from when the main power of image forming apparatus 100 is turned on to when it is turned off reaches a predetermined time. Alternatively, CPU 313 may execute the update process each time the accumulated time during which the main power of image forming apparatus 100 is ON reaches a predetermined time. In other words, when the predetermined condition is satisfied, the CPU 313 forms the patch image 2 by the printer 101 and executes update processing in order to update the reference density and the reference detection value.

Further, the updating process of this embodiment may be configured such that the user inputs an execution instruction from the operation panel 20 . FIG. 15 shows a simple calibration screen displayed on the liquid crystal display 218 .

When the user presses the user mode button on the operation panel 20, the CPU 313 displays a simple calibration screen on the liquid crystal display 218. FIG. On this screen, the user can instruct execution of update processing. Furthermore, this screen displays a status 451 indicating the remaining number of image formation sheets until the next update process is executed. The status 451 sets the update timing of the reference density to the timing when the cumulative number of images formed reaches 10,000 pages. Status 451 shown in FIG. 15 is 80%. In other words, the image forming apparatus 100 is scheduled to print about 8000 pages of images.

In this way, the liquid crystal display 218 displays the parameters until the update processing of the reference density becomes necessary, so that the user can be roughly notified of the update timing. Furthermore, on the simple calibration screen, even before the update timing, it is possible for the user to change the timing for executing the update processing according to his/her convenience. When the user presses the OK button 452, the CPU 313 executes update processing even if the cumulative number of formed images has not reached the predetermined number. This allows the user to execute update processing at desired timing. Note that when the user presses the cancel button 453, a screen different from the simple calibration screen is displayed on the liquid crystal display 218. FIG.

In addition, the model formula of the present embodiment obtains the concentration fluctuation amount based on the detection value of the environment sensor 199 and the detection value of the inductance sensor 200 . However, for example, the model formula may be configured such that input values are the detection value of the environment sensor 199, the idle time measured by the timer 201, and the number of times of replenishment measured by the counter 202. FIG. Alternatively, the model formula may be a formula in which input values of the temperature of the developing device 4 and the humidity of the developing device 4 are added.

Further, the image density sensor 400 of the present embodiment is configured to measure the patch image formed on the intermediate transfer belt 6, but for example, the image density sensor 400 measures the patch image formed on each photosensitive drum 1. It is good also as a structure which carries out. That is, the image density sensor 400 measures the image for measurement carried on the photosensitive drum 1 (or the intermediate transfer belt 6), which is an image carrier.

Further, although the image forming apparatus 100 of this embodiment is configured to include the CPU 313, the image processing unit 110, and the CPU 120, the number of processors is not limited to this. A configuration including a processor for controlling the image processing unit 110 may be employed, or a configuration in which the CPU 313 controls the printer 101 without the CPU 120 may be employed. Alternatively, each function of the printer controller 300 may be controlled by an individual ASIC.

A reader 101 printer 300 printer controller 400 image density sensor

Claims (4)

image forming means having a developer containing developer containing toner and carrier, and forming an image on a sheet using the developer in the developer;
a storage means;
a sensor for detecting the toner density of the developer in the developing device;
an image carrier on which an image for measurement formed by the image forming means is carried;
measuring means for measuring the measurement image on the image carrier;
The image forming conditions for causing the image forming means to form a pattern image on a sheet, acquiring read data relating to the pattern image output from a reading device, and controlling the density of the image formed by the image forming means are set as described above. a first generation means for generating based on read data;
causing the image forming means to form a first image for measurement based on the image forming conditions generated by the first generating means; causing the measuring means to measure the first image for measurement; a control means for storing the measurement result of the image for measurement as a reference density in the storage means;
determining an amount of density variation from the reference density based on the detection result of the sensor, and calculating a predicted density of an image formed by the image forming means based on the reference density and the density variation stored in the storage means; a second generation means for determining and generating the image forming conditions based on the predicted density;
When the number of sheets on which images are formed by the image forming means reaches a predetermined number, the image forming means is caused to form a second image for measurement, the measuring means is caused to measure the second image for measurement, and the and correction means for correcting the reference density based on the measurement result of the second measurement image by the measurement means. the sensor outputs a detection value that varies according to the toner concentration;
The generation means determines the amount of density variation based on the detection value output from the sensor and a reference detection value output from the sensor when the reference density is stored in the storage means. The image forming apparatus according to claim 1, characterized by: further comprising conversion means for converting image data based on conversion conditions;
The image forming means forms the image based on the image data converted by the converting means,
2. The image forming apparatus according to claim 1, wherein the image forming conditions include the conversion conditions. The conversion means converts an image signal included in the image data based on the conversion condition,
4. The image forming apparatus according to claim 3 , wherein said generator determines the amount of density variation for each of a plurality of different image signal values based on the detection result of said sensor.

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