Image forming apparatus

Abstract

To determine respective image forming conditions for a plurality of target maximum densities with good efficiency and accuracy.SOLUTION: An image forming apparatus forms a test image on an image carrier or a sheet, and detects the density of the test image. The image forming apparatus determines a first image forming condition according to which a first maximum density can be achieved and a second image forming condition according to which a second maximum density can be achieved, from the relationship between N densities detected from N toner patterns included in the test image and N image forming conditions set for forming the respective N toner patterns.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a calibration technique for an image forming apparatus. [Background technology]

[0002] An image forming apparatus forms a test image so that the density of an image formed by the image forming apparatus is a desired density, and adjusts image forming conditions based on the results of reading the test image. This is called calibration.

[0003] Incidentally, one image forming apparatus may be used for different purposes. The different purposes include, for example, both printing of printed matter with image quality required in a general office and printing of high-quality catalogs. For example, for printed matter with image quality required in a general office, image forming conditions that suppress the consumption of toner (or ink) are used. For example, for high-quality catalogs, image forming conditions that increase the consumption of toner and improve the color gamut of printed matter rather than suppressing the consumption of toner are used. Therefore, in an image forming apparatus that can be used for different purposes, in order to form images with different target densities, it is necessary to control switching of image forming conditions according to the target densities. Patent Document 1 proposes correcting the image forming conditions for each page when the target densities are different for each page. Patent Document 2 proposes forming a test image using a plurality of different image forming conditions (exposure amount, charging bias voltage, developing bias voltage) and adjusting the image forming conditions so that the target maximum density can be achieved. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-44740 A [Patent Document 2] JP 2018-132544 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the technology of Patent Document 1, a test image is actually formed between pages to adjust the image forming conditions for one target maximum density, and the first image forming conditions are reused to adjust the image forming conditions for the other target maximum density. A test image is not formed between pages for the image forming conditions for the other target maximum density. Therefore, even if the image forming conditions are controlled to the image forming conditions for the other target maximum density, the maximum density of the image formed by the image forming device may not be the target maximum density of the other. In the technology of Patent Document 2, calibration of the image forming conditions is performed for each target maximum density. When there are N target maximum densities, N calibrations are required. Therefore, it takes a long time to complete all the calibrations.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to determine image forming conditions for each of a plurality of target maximum densities efficiently and accurately. [Means for solving the problem]

[0007] The present invention relates to, for example, A photoconductor; a charging means for charging the photoconductor using a charging voltage; an exposure unit that irradiates the photoconductor with light of a set exposure amount to form an electrostatic latent image; a developing means for developing the electrostatic latent image with toner by using a developing voltage to form a toner image; an acquisition unit for acquiring a density of a test image formed on the photoconductor, the test image transferred from the photoconductor to an intermediate transfer body, or the test image formed on a sheet; a determining unit for determining a plurality of image forming conditions capable of achieving a plurality of different maximum densities based on the density, The test image includes N toner patterns formed under different image forming conditions, The determining means is An image forming device is provided that is configured to determine a first image forming condition capable of achieving a first maximum density and a second image forming condition capable of achieving a second maximum density from the relationship between N densities detected from the N toner patterns and N image forming conditions set for forming each of the N toner patterns. Effect of the Invention

[0008] According to the present invention, it is possible to determine image forming conditions for each of a plurality of target maximum densities efficiently and accurately. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating an image forming apparatus. [Diagram 2] A diagram illustrating an image forming station [Diagram 3] FIG. 1 is a diagram illustrating an image reading device. [Figure 4] A diagram explaining a control circuit. [Diagram 5] A diagram explaining the target maximum density and image formation conditions for each mode [Figure 6] Diagram explaining a concentration sensor [Figure 7] Diagram explaining test images [Figure 8] FIG. 1 is a diagram illustrating a concentration conversion table. [Figure 9] Flowchart showing maximum density control [Figure 10] A diagram showing conditions for creating a toner pattern. [Figure 11] A diagram explaining the Vc conversion table [Figure 12] Diagram showing how to calculate development contrast [Figure 13] FIG. 1 is a diagram illustrating the effects of an embodiment and a comparative example. [Figure 14] Diagram explaining the test chart [Figure 15] Flowchart showing maximum density control [Figure 16] Diagram explaining the user interface [Figure 17] FIG. 1 is a diagram illustrating the relationship between measured density values ​​and image forming conditions. [Figure 18] Diagram explaining the functions of a CPU DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0011] <Example 1> [Image forming device] The image forming apparatus 100 shown in FIG. 1 is an electrophotographic color multifunction machine that employs a contact charging method and a two-component contact development method. The image forming apparatus 100 has an exposure device 3 and four image forming stations Pa, Pb, Pc, and Pd. The exposure device 3 deflects laser beams La, Lb, Lc, and Ld output from a light source 31 using a rotary polygon mirror 32, and supplies the laser beams La, Lb, Lc, and Ld to the image forming stations Pa, Pb, Pc, and Pd. The image forming station Pa forms a yellow (Y) toner image based on the laser beam La and transfers it to the intermediate transfer belt 11. The image forming station Pb forms a magenta (M) toner image based on the laser beam Lb and transfers it to the intermediate transfer belt 11. The image forming station Pc forms a cyan (C) toner image based on the laser beam Lc and transfers it to the intermediate transfer belt 11. The image forming station Pd forms a black (K) toner image based on the laser light Ld and transfers it to the intermediate transfer belt 11. The intermediate transfer belt 11 conveys a color image formed by superimposing the yellow (Y), magenta (M), cyan (C), and black (K) toner images to a secondary transfer roller 12.

[0012] The sheet cassette 14 stores a large number of sheets P. The feed rollers 15 feed the sheets P from the sheet cassette 14 to a conveying path. In the conveying path, a plurality of conveying roller pairs 16 convey the sheets P to the secondary transfer roller 12.

[0013] The secondary transfer roller 12 forms a secondary transfer nip by contacting with the intermediate transfer belt 11. When the sheet P passes through the secondary transfer nip, the toner image is transferred from the intermediate transfer belt 11 to the sheet P.

[0014] The fixing device 9 fixes the toner image onto the sheet P. The discharge section 17 has, for example, a pair of discharge rollers, and discharges the sheet P to the outside of the image forming apparatus 100.

[0015] The image reading device 110 reads an original and generates image data. The operation unit 120 receives instructions input by a user and displays messages to the user.

[0016] The density sensor 50 is disposed so as to face the image transport surface of the intermediate transfer belt 11, and detects the density (optical density) of the toner image transferred to the image transport surface of the intermediate transfer belt 11. For example, the image forming apparatus 100 performs calibration of a target maximum density (hereinafter simply referred to as maximum density) based on the density detected from a test image. In other words, the image forming conditions are adjusted so that the maximum density of the toner image formed on the sheet P (image density when the density signal (image printing rate) is 100%) becomes a target value.

[0017] [Image forming station] 2 shows a schematic cross section of the image forming stations Pa to Pd. The four image forming stations Pa, Pb, Pc, and Pd have the same structure. Around the photosensitive drum 1, which is an image carrier, there are arranged a charging roller 2, an exposure device 3, a developing device 4, and a primary transfer roller 7a. The photosensitive drum 1, the charging roller 2, the developing sleeve 41, and the primary transfer roller 7 rotate in the directions indicated by the arrows.

[0018] A charging bias voltage Vd is applied to the charging roller 2 from a high-voltage power supply 101, and uniformly charges the surface of the photosensitive drum 1. An exposure device 3 irradiates the surface of the photosensitive drum 1 with laser light L modulated according to image data, and forms an electrostatic latent image corresponding to the image data.

[0019] The developing device 4 reversely develops the toner image by attaching toner to the electrostatic latent image. The developing device 4 has a container 40 for storing toner, a stirring screw 42 for stirring the toner and carrier, and a developing sleeve 41 arranged opposite the photosensitive drum 1. The container 40 stores, for example, a two-component developer in which non-magnetic toner and magnetic carrier are mixed at a predetermined ratio. A developing bias voltage Vdc is applied to the core of the developing sleeve 41 from a high-voltage power source 102. The developing bias voltage Vdc is a voltage that promotes the development of the toner image.

[0020] As the photosensitive drum 1 rotates, the toner image is transported to the primary transfer nip. The primary transfer nip is formed by the contact between the primary transfer roller 7 and the photosensitive drum 1. A high-voltage power supply 103 applies a primary transfer bias voltage Vpr to the primary transfer roller 7. This promotes the primary transfer of the toner image from the photosensitive drum 1 to the intermediate transfer belt 11.

[0021] The both ends of the core of the charging roller 2 are rotatably held by bearing members (not shown). Furthermore, both ends of the core are urged toward the photosensitive drum 1 by a pressure spring 21. That is, the charging roller 2 is pressed against the surface of the photosensitive drum 1 with a predetermined pressure. As a result, the charging roller 2 rotates following the rotation of the photosensitive drum 1. The charging bias voltage Vd is, for example, an oscillating voltage in which a DC voltage and an AC voltage are superimposed. For example, the waveform of the AC voltage is a sine wave. The frequency of the AC voltage is 1.3 kHz. The peak-to-peak voltage Vpp of the AC voltage is 1.5 kV. The DC voltage is, for example, -600 V. In this case, the surface potential of the photosensitive drum 1 becomes -600 V (dark potential), which is the same as the DC voltage applied to the charging roller 2.

[0022] The developing device 4 uses a negative non-magnetic toner, for example. The developing sleeve 41 is a non-magnetic developer carrier. A part of the outer circumferential surface of the developing sleeve 41 is exposed to the outside of the developing device 4. The closest distance (SD gap) between the developing sleeve 41 and the photosensitive drum 1 is, for example, 260 μm. The opposing portion between the photosensitive drum 1 and the developing sleeve 41 can be called a developing portion. The developing bias voltage Vdc is an oscillating voltage in which a DC voltage and an AC voltage are superimposed. The DC voltage is, for example, −450 V. The frequency of the AC voltage is 8.0 kH. The peak-to-peak voltage Vpp of the AC voltage is 1.8 kV. The waveform of the AC voltage is a square wave. The electrostatic latent image is inverted and developed by an electric field generated between the developing bias Vdc and the electrostatic latent image formed on the surface of the photosensitive drum 1.

[0023] The primary transfer bias voltage Vpr is a voltage of positive polarity, which is opposite to the charge polarity (negative polarity) of the toner. For example, the primary transfer bias voltage Vpr is +1 kV.

[0024] In addition, when detecting the density of the toner image formed on the photosensitive drum 1, the density sensor 50 is provided facing the surface of the photosensitive drum 1. That is, the density sensor 50 is disposed between the developing device 4 and the primary transfer nip.

[0025] [Image reader] 3 shows image reading device 110. Image reading device 110 includes a first mirror unit 301, a second mirror unit 302, an image sensor 303, a lens 304, a motor 305, a size sensor 306, and a home position sensor 307. First mirror unit 301 includes an illumination light source 311 and a first mirror 312. Second mirror unit 302 includes a second mirror 313 and a third mirror 314. First mirror unit 301 and second mirror unit 302 are driven by motor 305 to move in the +Z direction and the -Z direction.

[0026] When the original 390 is placed on the platen glass 310, the motor 305 rotates, and the first mirror unit 301 and the second mirror unit 302 move to the home position. The home position sensor 307 detects that the first mirror unit 301 and the second mirror unit 302 have moved to the home position. Next, the illumination light source 311 is turned on and irradiates the reading surface of the original 390 with light. While the first mirror unit 301 and the second mirror unit 302 move in the Z direction, the first mirror 312, the second mirror 313, and the third mirror 314 guide the light from the original 390 to the lens 3054. The lens 304 forms an image of the light on the light receiving surface of the image sensor 303. The image sensor 303 converts the light into an electrical signal.

[0027] [Block diagram] 4 is a schematic functional block diagram showing a control circuit 400 of the image forming apparatus 100. The CPU 401 is a processor (processing circuit) that controls each unit of the image forming apparatus 100 in accordance with a control program. The CPU 401 also includes a built-in memory 490 that stores data.

[0028] The density signal generating unit 402 includes a circuit that converts image data supplied from the print image processing unit 414 into a density signal (laser control signal) and supplies it to the exposure device 3. The density signal generating unit 402 also includes a generating unit that generates a density signal of a test image used to determine image formation conditions capable of achieving a target maximum density. The exposure device 3 drives a laser element based on the density signal sent from the density signal generating unit 402, and outputs laser beams La to Ld.

[0029] The reading control unit 406 includes a circuit that controls ON / OFF of the illumination light source 311 of the image reading device 110 and driving of the motor 305 in accordance with a command signal from the CPU 401. The read image processing unit 405 includes a circuit that acquires an electrical signal from the image sensor 303 of the image reading device 110, generates an image signal, and sends it to the CPU 401. For example, the read image processing unit 405 converts the electrical signal into an image signal using a lookup table LUTid.

[0030] Motor control unit 407 operates various motors in accordance with command signals from CPU 401. These include a motor that drives feed roller 15, a motor that drives transport roller pair 16, a motor that drives image forming station P, a motor that drives intermediate transfer belt 11, and a motor that drives fixing device 9. High voltage control unit 408 controls high voltage power supplies 101, 102, and 103 in accordance with command signals from CPU 401.

[0031] The CPU 401 is electrically connected to the I / F unit 409 and the timer 410. The CPU 401 is connected to the operation unit 120 through the I / F unit 409. The operation unit 120 has a display device 411 and an input device 412. The display device 411 is a liquid crystal display or an organic EL display. The input device 412 can include a keyboard, a touch sensor, and the like. The operation unit 120 may be an external terminal such as a personal computer connected to the image forming apparatus 100.

[0032] The CPU 401 is also electrically connected to the controller 413 and the print image processing unit 414. The CPU 401 receives image information 415 through the controller 413. The image information 415 is received, for example, from a PC 450 such as a host computer. PC is an abbreviation for personal computer. The CPU 401 processes the image information 415 in the print image processing unit 414 to generate image data, and outputs the image data to the density signal generating unit 402. As a result, an image corresponding to the image information 415 is formed on the sheet P. The print image processing unit 414, for example, develops the image information 415 into a bitmap image, or converts the color space of the image information 415 (e.g., RGB->YMCK). The density signal generating unit 402 corrects the gradation characteristics of the image data using a gamma correction table, or binarizes the image data using a predetermined dither matrix.

[0033] [How to change the target maximum density for each job] As explained at the beginning, the maximum density for production printing is higher than the maximum density for office printing, and in other cases, users may wish to switch the maximum density for each job.

[0034] 5 is a table 500 showing the relationship between the target maximum density (mode) and the image forming conditions. The table 500 is stored in the memory 490, for example.

[0035] A printer driver compatible with image forming apparatus 100 is executed in PC 450. The printer driver selects mode A or mode B for each job and instructs image forming apparatus 100 to execute the print job. When mode A is selected, PC 450 adds Target A (=1.50) to image information 415 as the target maximum density. When mode B is selected, PC 450 adds Target B (=1.60) to image information 415 as the target maximum density. Image information 415 including the target maximum density is passed to CPU 401 via controller 413.

[0036] The CPU 401 processes the received image information 415 in the print image processing unit 414. As a result, image forming conditions (e.g., exposure amount LPW, charging bias voltage Vd, and developing bias voltage Vdc) are set so that image conditions (developing contrast Vc) corresponding to the target maximum density are obtained. For example, assume that identification information of mode A or Target A is added to the image information 415. In this case, the CPU 401 or the print image processing unit 414 refers to the table 500 and acquires the charging bias voltage Vd_A, developing bias voltage Vdc_A, and exposure amount LPW_A associated with Target A. The CPU 401 sets the charging bias voltage Vd_A to the high voltage power supply 101 through the high voltage control unit 408. The CPU 401 sets the developing bias voltage Vdc_A to the high voltage power supply 102 through the high voltage control unit 408. Furthermore, the CPU 401 sets the exposure amount LPW_A to the exposure device 3.

[0037] Identification information of mode B or Target B may be added to the image information 415. In this case, the CPU 401 or the print image processing unit 414 refers to the table 500 and acquires the charging bias voltage Vd_B, the developing bias voltage Vdc_B, ​​and the exposure amount LPW_B associated with Target B. The CPU 401 sets the charging bias voltage Vd_B to the high voltage power supply 101 through the high voltage control unit 408. The CPU 401 sets the developing bias voltage Vdc_B to the high voltage power supply 102 through the high voltage control unit 408. Furthermore, the CPU 401 sets the exposure amount LPW_B to the exposure device 3.

[0038] The print image processing unit 414 may use a different gamma correction table (LUT) for each maximum target density. The print image processing unit 414 may use the same gamma correction table even if the maximum target density is different. Here, it is assumed that the same gamma correction table is used for mode A and mode B. Note that there are cases where different gamma correction tables are used for mode A and mode B. In this case, a gamma correction table is created using the image formation conditions associated with mode A, and another gamma correction table is created using the image formation conditions associated with mode B.

[0039] Here, two target maximum concentrations are illustrated, but this is merely an example. The number of target maximum concentrations may be three or more.

[0040] [Concentration sensor] FIG. 6 is a schematic diagram showing the density sensor 50. The density sensor 50 shown in FIG. 6 is a specular reflection type sensor that detects specularly reflected light from the toner pattern PT. The light emitting element 601 is an element (e.g., a light emitting diode) that outputs light toward a predetermined measurement position. The light receiving element 602 is an element (e.g., a photodiode) that receives specularly reflected light from the toner pattern PT or the intermediate transfer belt 11 that passes the measurement position. The density sensor 50 further has an IC 603 that controls the amount of light emitted (amount of irradiation light) of the light emitting element 601 as one of the irradiation conditions. IC is an abbreviation for integrated circuit.

[0041] The light emitting element 601 is disposed so that the optical axis of the light emitting element 601 is at an angle of 45 degrees with respect to the normal line of the intermediate transfer belt 11. The light receiving element 602 is disposed so as to be linearly symmetrical with the light emitting element 601 with respect to the normal line of the intermediate transfer belt 11. The light receiving element 602 outputs a current according to the light receiving result (reflected light level). The IC 603 converts this current into a voltage, and further converts the voltage into a digital value and transmits it to the CPU 401.

[0042] 6 shows an example in which one toner pattern PT included in a test image passes through a measurement position. The print image processing unit 414 has a conversion table that converts the output value (brightness value) of the density sensor 50 into the density value of the toner pattern PT. Therefore, the CPU 401 passes the output value of the density sensor 50 to the print image processing unit 414 and converts it into a density value using the print image processing unit 414. Such a conversion process may be executed by the CPU 401. The conversion table is created in advance in accordance with the output characteristics of the density sensor 50 and is stored in a storage device or memory 490 in the print image processing unit 414.

[0043] The density sensor 50 may be a diffuse reflection type sensor that receives diffusely reflected light. A specular reflection type sensor can detect yellow, magenta, cyan, and black toners. However, when the image printing rate of the toner pattern PT approaches 100%, the detection accuracy may decrease. On the other hand, a diffuse reflection type sensor can detect yellow, magenta, and cyan toners even when the image printing rate is 100%. However, a diffuse reflection type sensor cannot detect black toner.

[0044] If manufacturing costs allow, the density sensor 50 may include both a specular reflection type sensor and a diffuse reflection type sensor, making it possible to accurately detect the toner patterns of yellow, magenta, cyan, and black even when the image printing rate is 100%.

[0045] [Maximum Density Control] Generally, density correction is roughly divided into maximum density control, which adjusts the development contrast Vc through the exposure amount LPW, the charging bias voltage Vd, the development bias voltage Vdc, etc., and gradation correction control, which corrects the input image data with a gamma correction table. This embodiment relates to maximum density control when there are multiple target maximum densities. In particular, the image forming apparatus 100 determines multiple image forming conditions that can respectively achieve multiple target maximum densities at once by maximum density control.

[0046] FIG. 7 shows a test image 700 for correcting the development contrast so as to achieve the target maximum density. The test image 700 includes N toner patterns PT_Yi formed by yellow toner and N toner patterns PT_Mi formed by magenta toner. Furthermore, the test image 700 includes N toner patterns PT_Ci formed by cyan toner and N toner patterns PT_Ki formed by black toner. i is an integer from 1 to N. The density sensor 50 detects the toner patterns PT passing through the measurement position. In this example, N is 5. The minimum value of N is 2. The larger N is, the higher the control accuracy is, but the longer the control time is. Therefore, N may be determined so as to achieve the control accuracy or control time targeted in the design.

[0047] An arrow F1 indicates the rotation direction of the intermediate transfer belt 11. The size of each toner pattern PT is, for example, 25 mm×25 mm. N toner patterns PT are formed for each color, but the image forming conditions used to form each toner pattern PT are different. For example, when forming N toner patterns PT, N combinations of exposure amount LPW, charging bias voltage Vd, and development bias voltage Vdc are prepared in advance. Note that each of the N combinations corresponds one-to-one to the N development contrasts Vc. In this example, five toner patterns PT are formed using five development contrasts Vc1, Vc2, Vc3, Vc4, and Vc5. Thus, the test image 700 has a total of 20 toner patterns PT.

[0048] Here, the image printing rates (density gradations) of the 20 toner patterns PT are all the same. As described above, if the image printing rate of the toner patterns PT is too high, it becomes difficult for the regular reflection type density sensor 50 to detect the toner patterns PT with high accuracy. Therefore, in the first embodiment, the image printing rate of the toner patterns PT is set to 80%. However, the target maximum density is the optical density when the image printing rate is 100%. Therefore, the CPU 401 needs to convert the detection result of the toner pattern PT formed at an image printing rate of 80% to the detection result of the toner pattern PT formed at an image printing rate of 100%. A conversion table for density conversion is created in advance and stored in the memory 490. The CPU 401 refers to this conversion table and converts the detection result of the toner pattern PT formed at an image printing rate of 80% to the detection result of the toner pattern PT formed at an image printing rate of 100%.

[0049] 8 is a graph showing the relationship between the density when the image printing rate is 80% and the density when the image printing rate is 100%, which have been obtained in advance. An approximation curve may be found from a plurality of plots previously obtained by experiment, and a function or conversion table representing this approximation curve may be created and stored in memory 490. Alternatively, another unmeasured point may be found by interpolation calculation from two measurement points.

[0050] For example, to achieve the maximum target density TargetA (=1.50) at 100% image printing rate, the density should be 1.20 at 80% image printing rate (dashed line). Similarly, to achieve the maximum target density TargetB (=1.60) at 100% image printing rate, the density should be 1.30 at 80% image printing rate (dashed line).

[0051] 9 is a flowchart showing maximum density control executed by CPU 401 according to a control program. When a user or serviceman inputs an instruction to execute maximum density control from operation unit 120, CPU 401 executes the following processes. Alternatively, CPU 401 executes the following processes when the cumulative number of image forming operations reaches or exceeds a threshold value. The following processes are executed independently for each color of YMCK.

[0052] In step S901, the CPU 401 starts up maximum density control. For example, the CPU 401 starts up a program module that is stored in the memory 490 and is responsible for maximum density control.

[0053] In S902, the CPU 401 transmits a command to form the toner pattern PT to the density signal generating unit 402, thereby forming a test image 700 on the intermediate transfer belt 11. In accordance with the command, the density signal generating unit 402 outputs a density signal for forming the test image 700, and sets image forming conditions for each toner pattern PT in the exposure device 3 and the high-voltage power supplies 101 and 102.

[0054] 10 shows the development contrast Vc of each toner pattern PT and the combination of the charging bias voltage Vd, the developing bias voltage Vdc, and the exposure amount LPW that achieves it. This combination is stored in advance in the memory 490. For example, the charging bias voltage Vd1 is -500V. Vd2 is -600V. Vd3 is -700V.

[0055] The developing bias voltage Vdc is determined taking into consideration the fog removing potential Vfog (=150V). Vdcj = Vdj + Vfog (1) where j is an integer between 1 and 3. In this example, Vfog is 150V, so Vdc1 is -350V. Vdc2 is -450V. Vdc3 is -550V.

[0056] The exposure amount LPW is converted into the surface light amount on the photosensitive drum 1. For example, LPW1 is 0.16 μJ / cm2. LPW2 is 0.24 μJ / cm2. LPW3 is 0.32 μJ / cm2. The above values ​​are all merely examples.

[0057] FIG. 11 shows a Vc conversion table 1100 representing the development contrast Vc corresponding to the combination of the charging bias voltage Vd and the exposure amount LPW. The Vc conversion table 1100 is created in advance according to the characteristics of the photosensitive drum 1, and is stored in the print image processing unit 414 or the memory 490. In the first embodiment, Vc1 is the development contrast corresponding to the combination of LPW1 (=0.16 μJ / cm2) and Vd1 (−500V). Therefore, as the arrow indicates, Vc1 is 90V. By the same procedure, Vc2 is 160V. Vc3 is 230V. Vc4 is 301V. Vc5 is 370V.

[0058] In S903, the CPU 401 detects the density of the toner pattern PT using the density sensor 50. As described above, the CPU 401 refers to the brightness-density conversion table held in the memory 490 and converts the output value of the density sensor 50 into a density value.

[0059] In S904, the CPU 401 obtains a development contrast Vc_A capable of achieving Target A and a development contrast Vc_B capable of achieving Target B. For example, a development contrast Vc_A is obtained in which the target maximum density is 1.50 when the image printing rate is 100% and the target maximum density is 1.20 when the image printing rate is 80%. Similarly, a development contrast Vc_B is obtained in which the target maximum density is 1.60 when the image printing rate is 100% and the target maximum density is 1.30 when the image printing rate is 80%.

[0060] 12 shows the relationship between the density values ​​of the five toner patterns PT acquired in step S903 and the development contrast Vc. The five plots have coordinates representing the development contrasts Vc1 to Vc5 set to generate the five toner patterns PT1 to PT5 and the density values ​​D1 to D5 acquired from the toner patterns PT1 to PT5, respectively.

[0061] The CPU 401 obtains the two density values ​​Di and Di+1 that are closest to Target A among the density values ​​D1 to D5 acquired from the toner patterns PT1 to PT5. In this example, the two density values ​​that are closest to Target A are D1 and D2. Therefore, the CPU 401 interpolates between the coordinates (Vc1, D1) and (Vc2, D2) to calculate the development contrast Vc_A that corresponds to Target A. As a result, Vc_A is calculated to be 131V.

[0062] The CPU 401 obtains the two density values ​​Di and Di+1 that are closest to Target B among the density values ​​D1 to D5 acquired from the toner patterns PT1 to PT5. In this example, the two density values ​​that are closest to Target B are D2 and D3. Therefore, the CPU 401 interpolates between the coordinates (Vc2, D2) and (Vc3, D3) to calculate the development contrast Vc_B that corresponds to Target B. As a result, Vc_B is calculated to be 179V.

[0063] In this manner, in the first embodiment, a development contrast Vc_A capable of achieving Target A and a development contrast Vc_B capable of achieving Target B are obtained by one maximum density control. Both development contrasts Vc_A and Vc_B are calculated from the test image 700, and therefore have higher accuracy than in the past. In addition, two development contrasts Vc_A and Vc_B are calculated from one test image 700, so that the control time is unlikely to increase.

[0064] In S905, the CPU 401 obtains an image forming condition A capable of achieving a development contrast Vc_A and an image forming condition B capable of achieving a development contrast Vc_B. In the first embodiment, the exposure amount LPW of the image forming condition A and the exposure amount LPW of the image forming condition B are set to be the same. Therefore, the CPU 401 determines the image forming conditions according to the following procedure. The reason why the exposure amount of the image forming condition A and the exposure amount of the image forming condition B are set to be the same is as follows. If the exposure amount LPW is different even though the potential setting is the same, the difference in gamma characteristics between the multiple image forming conditions becomes large. On the other hand, if the exposure amount LPW is the same but the potential setting is different, the difference in gamma characteristics between the multiple image forming conditions becomes small. Therefore, in the first embodiment, a common (same) gamma correction table is used for the image forming condition A and the image forming condition B. This eliminates the need to create a gamma correction table for each image forming condition, and the time required to create the gamma correction table is reduced.

[0065] (i) The CPU 401 obtains the charging bias voltage Vd and the exposure amount LPW of the image forming condition A from the development contrast Vc_A. The CPU 401 obtains the charging bias voltage Vd and the exposure amount LPW corresponding to the development contrast Vc_A by linearly interpolating between the coordinates of two image forming conditions close to the coordinates of the Target A. As described above, the density values ​​close to the Target A are D1 and D2. According to FIG. 10, it can be seen that the toner pattern PT1 is formed using the charging bias voltage Vd1, and the toner pattern PT2 is formed using the charging bias voltage Vd1. Therefore, the charging bias voltage Vd_A is determined to be Vd1 (=-500V). Similarly, according to FIG. 10, it can be seen that the toner pattern PT1 is formed using the exposure amount LPW1, and the toner pattern PT2 is formed using the exposure amount LPW2. According to FIG. 11, LPW1 is 0.16 μJ / cm2, and LPW2 is 0.24 μJ / cm2. Therefore, the CPU 401 determines the exposure amount LPW_A to be 0.21 μJ / cm 2 by interpolating between LPW1 and LPW2.

[0066] The developing bias voltage Vdc_A is determined to be −350 V from equation (1).

[0067] (ii) The CPU 401 substitutes the exposure amount LPW_A for the exposure amount LPW_B of the image forming condition B. That is, the exposure amount LPW_B becomes 0.21 μJ / cm 2 .

[0068] 11, the CPU 401 obtains the charging bias voltage Vd_B corresponding to the exposure amount LPW_B. That is, the charging bias voltage Vd_B for the exposure amount LPW_B (=0.21 μJ / cm2) at which the development contrast Vc_B is 179 V is obtained from the Vc conversion table 1100. As a result, the charging bias voltage Vd_B is calculated to be −575 V.

[0069] The developing bias voltage Vdc_B is determined to be −425 V from equation (1).

[0070] In S906, the CPU 401 stores image forming condition A and image forming condition B in the memory 490. The image forming condition A includes a development contrast Vc_A, a charging bias voltage Vd_A, a development bias voltage Vdc_A, and an exposure amount LPW_A. The image forming condition B includes a development contrast Vc_B, a charging bias voltage Vd_B, a development bias voltage Vdc_B, ​​and an exposure amount LPW_B. Note that, for the image forming condition B, a difference amount ΔVc of the development contrast Vc_B with respect to the development contrast Vc_A may be stored in the memory 490 instead of the development contrast Vc_B.

[0071] In the first embodiment, it is assumed that the exposure amount LPW_A under the image forming condition A is the same as the exposure amount LPW_B under the image forming condition B. However, the exposure amount LPW_A under the image forming condition A may be different from the exposure amount LPW_B under the image forming condition B. In this case, the procedure (ii) is replaced with the procedure (i) for the image forming condition B as well. In other words, the procedure (i) used to obtain the image forming condition A is also applied to the image forming condition B.

[0072] [effect] According to the first embodiment, it is possible to determine the image forming conditions for each of a plurality of target maximum densities by only executing the maximum density control once. Therefore, it is possible to obtain the image forming conditions for each of a plurality of target maximum densities without increasing the control time.

[0073] 13 shows the number of executions of the maximum density control in the comparative example and the number of executions of the maximum density control in the embodiment 1. The comparative example shows that one execution of the maximum density control is required to determine the image forming conditions for one target maximum density. Therefore, in the comparative example, N executions of the maximum density control are required to determine the image forming conditions for N target maximum densities.

[0074] On the other hand, in the first embodiment, one maximum density control is required to determine the image forming conditions for N target maximum densities. Therefore, in the first embodiment, it is possible to reduce the control time compared to the comparative example.

[0075] <Example 2> In the first embodiment, N image forming conditions that correspond one-to-one to N target maximum densities are determined by one maximum density control. It is difficult for the regular reflection type density sensor 50 to accurately detect the density of the toner pattern PT when the image printing rate is 100%. Therefore, in the first embodiment, the image forming conditions are obtained by setting the image printing rate to 80%. That is, the image forming conditions are determined based on the relationship between the density when the image printing rate is 80% and the density when the image printing rate is 100%. If the relationship between the density when the image printing rate is 80% and the density when the image printing rate is 100% deviates from the previously set relationship, the accuracy of determining the image forming conditions decreases.

[0076] Therefore, in the second embodiment, the image reading device 110 detects the density of the toner pattern PT by reading a test image formed on a sheet P. Therefore, image forming conditions capable of achieving a target maximum density using the toner pattern when the image printing rate is 100% are determined. Therefore, the determination accuracy of the second embodiment is expected to be higher than that of the first embodiment. The only difference between the second embodiment and the first embodiment is the density detection method in the maximum density control. Therefore, the description of the first embodiment is used for the description of the parts common to the first and second embodiments.

[0077] [Test Chart] FIG. 14 shows a test chart 1400 used in maximum density control in the second embodiment. The test chart 1400 is a sheet P on which a test image is formed. The test image includes a yellow toner pattern PT_Y, a mazeta toner pattern PT_M, a cyan toner pattern PT_C, and a black toner pattern PT_K. Each toner pattern PT is formed by a 100% density signal (image printing rate). The vertical length of the toner pattern PT is, for example, 8 mm. The horizontal length is, for example, 16 mm.

[0078] The test chart 1400 includes 60 toner patterns PT. That is, there are 15 toner patterns PT for each color of toner. The 15 toner patterns PT correspond to 15 combinations of five exposure amounts LPW1 to LPW5 and three charging bias voltages Vd1 to Vd3. As shown in formula (1), the three charging bias voltages Vd1 to Vd3 correspond to three developing bias voltages Vdc1 to Vdc3.

[0079] As shown in Fig. 14, five toner patterns PT are lined up along the main scanning direction, and the five toner patterns PT are formed by different exposure amounts LPW1 to LPW5, respectively. The exposure amount LPW1 is 0.16μJ / cm2 when converted into the surface light amount on the photosensitive drum 1. Similarly, the exposure amount LPW2 is 0.20μJ / cm2. The exposure amount LPW3 is 0.24μJ / cm2. The exposure amount LPW4 is 0.28μJ / cm2. The exposure amount LPW5 is 0.32μJ / cm2.

[0080] Three toner patterns PT for each color are aligned along the sub-scanning direction (the conveying direction of the sheet P). The charging bias voltage Vd1 is a DC voltage of -500V. The developing bias voltage Vdc1 is -350V. The primary transfer bias voltage Vpr1 is +1050V.

[0081] The charging bias voltage Vd2 is a DC voltage of −600 V. The developing bias voltage Vdc1 is −450 V. The primary transfer bias voltage Vpr2 is +950 V.

[0082] The charging bias voltage Vd2 is a DC voltage of −700 V. The developing bias voltage Vdc1 is −550 V. The primary transfer bias voltage Vpr3 is +850 V.

[0083] As described above, a sine wave AC voltage having a frequency of 1.3 kHz and a peak-to-peak voltage Vpp of 1.5 kV is superimposed on the charging bias voltage Vd. A square wave AC voltage having a frequency of 8.0 kHz and a peak-to-peak voltage Vpp of 1.8 kV is superimposed on the developing bias voltage Vdc. The CPU 401 sequentially changes the combination of the exposure conditions and the potential conditions based on the timer value of the timer 410. In this way, the test chart 1400 is formed.

[0084] 15 is a flow chart showing the maximum density control in the embodiment 2. The CPU 401 executes the following processes according to a control program stored in the ROM area of ​​the memory 490.

[0085] In step S1501, the CPU 401 starts up maximum density control. For example, the CPU 401 starts up a program module that is stored in the memory 490 and is responsible for maximum density control.

[0086] 16A shows a user interface 1600 displayed on the operation unit 120. A button 1601 is a button for instructing the CPU 401 to create a test chart 1400. A cancel button 1602 is a button for instructing the CPU 401 to end maximum density control without creating a test chart 1400. When it is detected that a user or a service person has touched the button 1601, the CPU 401 advances the process from S1501 to S1502.

[0087] In S1502, the CPU 401 controls the image forming apparatus 100 to create the test chart 1400. A user or a serviceman may specify the type of the sheet P (e.g., plain paper, thick paper, thin paper) to be subjected to the maximum density control through the operation unit 120. The CPU 401 reads out the image forming conditions associated with the specified type of the sheet P from the memory 490 and sets them in the image forming apparatus 100. The image forming conditions include, for example, the exposure amount LPW, the charging bias voltage Vd, the developing bias voltage Vdc, and the primary transfer bias voltage Vpr. The CPU 401 causes the feed roller 15 and the conveying roller pair 16 to convey the sheet P through the motor control unit 407. Meanwhile, the CPU 401 controls the density signal generating unit 402 to output a density signal corresponding to the test chart 1400 to the exposure device 3. As a result, the image forming stations Pa to Pd form toner images and transfer them to the intermediate transfer belt 11. Furthermore, the secondary transfer roller 12 transfers the toner image of the test chart 1400 to the sheet P. The fixing device 9 fixes the toner image onto the sheet P, and the sheet P is discharged outside the image forming apparatus 100. In this way, the test chart 1400 is completed.

[0088] In S1503, the CPU 401 displays guidance on the operation unit 120. Fig. 16(B) shows a user interface 1610 for displaying a guidance message 1611. The guidance message 1611 includes a message urging the user to place the test chart 1400 discharged to a sheet tray or the like on the platen glass 310 or the like. A button 1612 is a button for instructing the image reading device 110 to read the test chart 1400. A cancel button 1613 is a button for instructing the CPU 401 to close the user interface 1610 without reading the test chart 1400.

[0089] In S1504, the CPU 401 controls the image reading device 110 to read the test chart 1400. The reading resolution of the image reading device 110 is, for example, 600 dpi, and the bit depth is 8 bits. The image reading device 110 outputs an electrical signal (RGB signal) that is the reading result of the test chart 1400 to the read image processing unit 405.

[0090] In S1505, the CPU 401 obtains the density of the toner pattern PT based on the result of reading the test chart 1400. For example, the CPU 401 controls the read image processing unit 405 to convert the RGB signals of 60 toner patterns PT into density values. The read image processing unit 405 converts the RGB signals into density values ​​using a brightness-density conversion table LUTid stored in the internal memory or the memory 490.

[0091] Fig. 17 shows the measurement results (density value of the toner pattern PT) for one of the colors yellow, magenta, cyan, and black. Since there are 15 combinations of image forming conditions (toner patterns PT) for one color, there are 15 measurement results. In Fig. 17, five exposure amounts LPW are arranged horizontally. Three charging bias voltages Vd are arranged vertically. Therefore, there are 15 combinations of image forming conditions.

[0092] The measurement results enclosed in parentheses in FIG. 17 are not used to determine the development contrast Vc. In other words, the development contrast Vc is determined using the seven measurement results enclosed in thick lines in FIG. 17. Incidentally, the amount of change in the line width of a thin line depending on differences in exposure conditions is greater than the amount of change in the line width of a thin line depending on differences in potential conditions. Therefore, by determining the development contrasts Vc_A and Vc_B under the same exposure conditions as much as possible, a common line width can be obtained in modes A and B. In order to expect such an effect, seven measurement results (image formation conditions) are selected.

[0093] In S1506, the CPU 401 obtains a development contrast Vc_A capable of achieving Target A and a development contrast Vc_B capable of achieving Target B. For example, a development contrast Vc_A is obtained that provides a target maximum density of 1.50 when the image printing rate is 100%. Similarly, a development contrast Vc_B is obtained that provides a target maximum density of 1.60 when the image printing rate is 100%.

[0094] Seven development contrasts Vc1 to Vc7 are obtained from the seven density values ​​shown in Fig. 17. For example, Vc1 = 90V, Vc2 = 125V, Vc3 = 160V, Vc4 = 230V, Vc5 = 300V, Vc6 = 335V, and Vc7 = 370V. The specific method of determining these is the same as in the first embodiment. Furthermore, Vc_A = 153V and Vc_B = 208V are determined by linear interpolation similar to that in the first embodiment.

[0095] In this way, in the second embodiment, the development contrasts Vc_A and Vc_B that can realize different target maximum densities are determined by one maximum density control. Therefore, the control time is not likely to be long. Moreover, since the development contrasts Vc_A and Vc_B are both determined from the test chart 1400 that is actually formed, the determination accuracy is also high.

[0096] In S1507, the CPU 401 obtains image formation conditions A that can achieve the development contrast Vc_A and image formation conditions B that can achieve the development contrast Vc_B. Similar to Example 1, in Example 2, the image formation conditions A and the image formation conditions B are determined by the same method. As a result, a charging bias voltage Vd_A = -500 V, a development bias Vdc_A = -350 V, and an exposure amount LPW_A = 0.23 μJ / cm2 are obtained. The exposure amount LPW_B of the image formation conditions B is the same as the exposure amount LPW_A. Further, referring to the Vc conversion table 1100 shown in FIG. 11, the charging bias voltage Vd_B corresponding to the exposure amount LPW_B is obtained. The charging bias voltage Vd_B = -590 V. The development bias voltage Vdc_B = -440 V.

[0097] In S1508, the CPU 401 stores the image formation conditions A and B in the memory 490. Then, the CPU 401 displays a user interface 1620 as illustrated in FIG. 16(C) on the operation unit 120. The user interface 1620 includes a message indicating that the maximum density control has been completed. Further, the user interface 1620 has a return button 1621. The return button 1621 is a button that instructs the CPU 401 to close the user interface 1620.

[0098] [Effect] Example 2 also brings the same effects as Example 1. Further, in Example 2, compared with Example 1, the maximum density control is executed using the toner pattern PT with an image printing rate of 100%. Therefore, the control accuracy of Example 2 can be higher than the control accuracy of Example 1.

[0099] <Function of CPU> FIG. 18 shows a plurality of functions implemented by the CPU 401 according to the control program. As described above, some of these functions may be implemented in the printed image processing unit 414, the density signal generation unit 402, or the read image processing unit 405, etc. This is because the control time is shortened by executing predetermined control with a dedicated integrated circuit separated from the CPU 401.

[0100] 18, the functions described above the dashed line are used when forming an image on a sheet P based on any image data prepared by the user. The functions described below the dashed line are functions (calibration functions) for creating or updating image formation conditions and look-up tables (LUTs).

[0101] The maximum density switching unit 1801 switches the target maximum density corresponding to the mode identification information based on the mode identification information (e.g., mode i) added to the image information. As described above, the target maximum density of mode A is Target A, and the target maximum density of mode B is Target B. In this manner, the relationship between mode i and the target maximum density Target_i may be stored in the memory 490. As described in the first embodiment, the mode identification information may directly indicate the target maximum density.

[0102] The condition selection unit 1802 reads out the image formation condition i corresponding to the target maximum density from the memory 490, and sets it in the exposure device 3 and the high voltage power supplies 101, 102, etc. Therefore, the image formation condition is changed according to the mode designated by the user.

[0103] A gradation correction unit 1803 corrects the gradation characteristics of the input image data using an LUT (gamma correction table) stored in the memory 490, and outputs the output image data. As a result, the gradation characteristics of the image formed on the sheet P match the gradation characteristics of the image on the original. The LUT is switched according to the type of the sheet P. The LUT is periodically updated by an LUT creation unit 1830.

[0104] The maximum density control unit 1810 executes the maximum density control described in the embodiments 1 and 2. The test control unit 1811 controls the image forming apparatus 100 to form the test image 700 on the intermediate transfer belt 11 and to form the test chart 1400.

[0105] The density acquisition unit 1812 includes a conversion unit 1813 that converts the output value of the toner pattern PT detected by the density sensor 50 into a density value. A conversion unit 1814 converts the RGB signal output by the image reading device 110 reading the test chart 1400 into a YMCK density value, because density control is performed for each color.

[0106] The contrast determination unit 1815 determines the development contrast Vc_i corresponding to each of a plurality of target maximum densities based on the density value D of the toner pattern PT. As shown in Fig. 12, the development contrast Vc_j corresponding to Target_j is determined from a graph showing the relationship between the development contrast Vci used to generate the toner pattern PTi and the density value Di detected from the toner pattern PTi.

[0107] A condition determination unit 1816 determines an image forming condition j corresponding to the development contrast Vc_j. The condition determination unit 1816 determines an image forming condition j corresponding to the development contrast Vc_j by referring to the Vc conversion table shown in FIG. 11. A Vd determination unit 1817 determines a charging bias voltage Vdj corresponding to the development contrast Vc_j by referring to the Vc conversion table. A Vdc determination unit 1818 determines a development bias voltage Vdcj from the charging bias voltage Vdj based on the formula (1). An LPW determination unit 1819 determines an exposure amount LPWj corresponding to the development contrast Vc_j by referring to the Vc conversion table. Note that the multiple exposure amounts to be determined may all be equal.

[0108] The storage unit 1820 stores the image forming conditions in association with the mode identification information or the target maximum density in the memory 490. In this way, the condition selection unit 1802 acquires appropriate image forming conditions from the memory 490 based on the mode identification information or the target maximum density.

[0109] <Technical ideas derived from examples> [Item 1] A first image forming condition capable of achieving a first maximum density and a second image forming condition capable of achieving a second maximum density may be determined from the relationship between the N densities obtained from the N toner patterns and the N image forming conditions set for forming each of the N toner patterns. This makes it possible to efficiently and accurately determine the image forming conditions (development contrast) for each of the multiple target maximum densities.

[0110] [Item 2] The N toner patterns may be formed by setting different development contrasts. In this case, a first development contrast capable of achieving a first maximum density and a second development contrast capable of achieving a second maximum density may be obtained from the relationship between the N densities acquired from the N toner patterns and the N development contrasts set for forming each of the N toner patterns. Furthermore, a first image forming condition capable of achieving the first development contrast and a second image forming condition capable of achieving the second development contrast may be obtained by referring to a plurality of known image forming conditions capable of achieving a plurality of specific development contrasts obtained in advance. As described with reference to FIG. 11, the Vc conversion table 1100 is an example of a plurality of known image forming conditions. This allows the image forming conditions (excluding the development contrasts) for each of a plurality of target maximum densities to be determined efficiently and accurately.

[0111] [Item 3] The charging bias voltage is an example of a charging voltage. The developing bias voltage is an example of a developing voltage. As described in the first embodiment, by making the exposure amount LPW_A and the exposure amount LPW_B equal, the image forming conditions are determined in a shorter time.

[0112] [Item 4] By substituting the exposure amount LPW_A for the exposure amount LPW_B, the image forming conditions are determined in a shorter time.

[0113] [Item 5] The predetermined coefficient may be a voltage set to reduce the toner fogging phenomenon, which makes it possible to easily obtain the development voltage.

[0114] [Item 6] The Vc conversion table 1100 may be stored in a storage device such as the memory 490. When a specific development contrast is not included in the Vc conversion table 1100, the CPU 401 may obtain the exposure amount and charging voltage corresponding to the specific development contrast by an interpolation calculation.

[0115] [Item 7] The first and second exposure amounts may be different from each other. In this case, the control time becomes longer, but the image forming conditions can still be determined accurately and in a short time.

[0116] [Item 8] The development contrast may be determined by an interpolation calculation, which makes it possible to determine the development contrast with a small number of measurement results and a small amount of calculation.

[0117] [Item 9] As explained in the first embodiment, by making the exposure amount LPW_A and the exposure amount LPW_B equal, it becomes possible for modes A and B to use a common gamma correction table (LUT).

[0118] [Item 10] The production print mode is an example of the first mode, and the office print mode is an example of the second mode. In this way, the maximum density may differ between production prints and office prints. In such cases, this embodiment is effectively used. These modes are merely examples. There may be three or more modes.

[0119] [Item 11] As described in the first embodiment, the concentration sensor 50 is an example of the detection means.

[0120] [Item 12] The regular reflection type density sensor 50 cannot accurately detect the density of a toner pattern formed at an image printing rate of 100%. Therefore, a test image is formed at an image printing rate of a predetermined percentage (e.g., 80%) that is lower than 100%. In this case, however, the detection result of the test image formed with a density signal of the predetermined percentage must be converted into the detection result of a test image formed with a density signal of 100%. The conversion unit 1813 may be responsible for such conversion processing.

[0121] [Item 13] Alternatively, a test image may be formed on a sheet with an image forming value of 100, read, and the read result may be converted to density. By using the image reading device 110 in this way, it is possible to create a test chart with a 100% density signal.

[0122] [Item 14] A message may be output to prompt the operator to input an instruction to output a test image and to read the sheet on which the test image is fixed. For example, manual labor is required to supply the test chart 1400 from the image forming apparatus 100 to the image reading apparatus 110. As shown in Fig. 16(B), displaying the message makes it possible to smoothly determine the image formation conditions.

[0123] The invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0124] 1: photosensitive drum, 2: charging roller, 3: exposure device, 4: developing device, 401: CPU

Claims

1. A photoconductor; a charging means for charging the photoconductor using a charging voltage; an exposure unit that irradiates the photoconductor with light of a set exposure amount to form an electrostatic latent image; a developing means for developing the electrostatic latent image with toner by using a developing voltage to form a toner image; an acquisition unit for acquiring a density of a test image formed on the photoconductor, the test image transferred from the photoconductor to an intermediate transfer body, or the test image formed on a sheet; a determining unit for determining a plurality of image forming conditions capable of achieving a plurality of different maximum densities based on the density, The test image includes N toner patterns formed under different image forming conditions, The determining means is The image forming device is configured to determine a first image forming condition capable of achieving a first maximum density and a second image forming condition capable of achieving a second maximum density from the relationship between the N densities obtained from the N toner patterns and the N image forming conditions set for forming each of the N toner patterns.

2. The N toner patterns are formed by setting different development contrasts, The determining means is determining a first development contrast capable of achieving a first maximum density and a second development contrast capable of achieving a second maximum density from a relationship between the N densities obtained from the N toner patterns and the N development contrasts set for forming the N toner patterns, respectively; determining a first image forming condition capable of achieving the first development contrast and a second image forming condition capable of achieving the second development contrast by referring to a plurality of known image forming conditions capable of achieving a plurality of specific development contrasts that have been previously determined; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured as follows.

3. the first image forming condition includes a first charging voltage, a first exposure amount, and a first developing voltage; the second image forming conditions include a second charging voltage, a second exposure amount, and a second developing voltage; The determining means is determining a first exposure amount and a first charging voltage capable of achieving the first development contrast from a plurality of combinations of exposure amounts and charging voltages capable of achieving the plurality of specific development contrasts determined in advance, and further determining the first development voltage by applying a predetermined coefficient to the first charging voltage; determining, from the plurality of combinations, the second charging voltage capable of achieving the second development contrast in combination with the second exposure amount equal to the first exposure amount, and further determining the second development voltage by applying the predetermined coefficient to the second charging voltage; 3. The image forming apparatus according to claim 2, wherein the image forming apparatus is configured as follows.

4. 4. The image forming apparatus according to claim 3, wherein the determining unit is configured to determine the second amount of exposure by substituting the first amount of exposure for the second amount of exposure.

5. 4. The image forming apparatus according to claim 3, wherein the predetermined coefficient is a voltage set to reduce toner fogging.

6. The developing device further includes a storage means for storing a conversion table that holds a plurality of development contrasts corresponding to combinations of different exposure amounts and different charging voltages, The determining means is find two development contrasts close to the first development contrast in the conversion table, and interpolate combinations of exposure amounts and charging voltages corresponding to the two development contrasts close to the first development contrast to obtain the first exposure amount and the first charging voltage capable of achieving the first development contrast; 4. The image forming apparatus according to claim 3, wherein the image forming apparatus is configured as follows.

7. the first image forming condition includes a first charging voltage, a first exposure amount, and a first developing voltage; the second image forming conditions include a second charging voltage, a second exposure amount, and a second developing voltage; The determining means is determining a first exposure amount and a first charging voltage capable of achieving the first development contrast by referring to a plurality of combinations of the exposure amount and the charging voltage capable of achieving the predetermined specific development contrast, and further determining the first development voltage by applying a predetermined coefficient to the first charging voltage; determining the second exposure amount and the second charging voltage capable of achieving the second development contrast by referring to the plurality of combinations, and further determining the second development voltage by applying the predetermined coefficient to the second charging voltage; 3. The image forming apparatus according to claim 2, wherein the image forming apparatus is configured as follows.

8. The determining means is selecting two densities that are close to the first maximum density from the N densities obtained from the N toner patterns; determining the first development contrast capable of achieving the first maximum density by interpolating between two development contrasts corresponding to the two densities close to the first maximum density; selecting two densities that are close to the second maximum density from the N densities obtained from the N toner patterns; 3. The image forming apparatus according to claim 2, wherein the second development contrast capable of achieving the second maximum density is obtained by interpolating between two development contrasts corresponding to the two densities close to the second maximum density.

9. The method further includes a gradation correction unit that performs gradation correction on any image data prepared by a user using the gradation correction conditions, 4. The image forming apparatus according to claim 3, wherein the gradation correction means is configured to use the same gradation correction conditions when the user specifies a first mode using the first maximum density and when the user specifies a second mode using the second maximum density.

10. the first maximum concentration is a maximum concentration for a first mode; 2. The image forming apparatus of claim 1, wherein the second maximum density is a maximum density for a second mode different from the first mode.

11. 3. The image forming apparatus according to claim 2, wherein the acquiring means comprises a detecting means for detecting specularly reflected light from the test image formed on the photoconductor or the test image transferred to the intermediate transfer body.

12. a supply means capable of supplying to said exposure means a density signal taking a value between 0% and 100% in accordance with input image data, said supply means supplying to said exposure means a density signal of a predetermined percentage lower than 100% when forming said test image; a conversion unit that converts the density of the test image formed using the density signal of the predetermined percentage and detected by the detection unit into the density of the test image formed using a density signal of 100%, 12. The image forming apparatus according to claim 11, wherein the determining unit is configured to determine the first developing contrast and the second developing contrast by using the density output from the converting unit.

13. a primary transfer means for transferring the toner image to an intermediate transfer body; a secondary transfer means for transferring the toner image from the intermediate transfer body to a sheet; a fixing means for fixing the toner image onto the sheet; and an image reading means for reading a test image, which is the toner image fixed on the sheet, 2. The image forming apparatus according to claim 1, wherein said acquiring means includes a converting means for converting the read result of said image reading means into a density.

14. 14. The image forming apparatus according to claim 13, further comprising an output unit that outputs a message prompting an operator to input an instruction to output the test image and to have the image reading unit read the sheet on which the test image is fixed.

15. A photoconductor; a charging means for charging the photoconductor using a charging voltage; an exposure unit that irradiates the photoconductor with light of a set exposure amount to form an electrostatic latent image; a developing means for developing the electrostatic latent image with toner by using a developing voltage to form a toner image; a transfer means for transferring the toner image to an intermediate transfer body; a detection means for detecting the density of a test image formed on the photoreceptor or the test image transferred to an intermediate transfer body; a determination unit for determining image forming conditions capable of achieving a plurality of different maximum densities based on the density, the image forming conditions including the charging voltage, the exposure amount, and the developing voltage; The test image includes N toner patterns formed by setting different development contrasts, The determining means is determining a first development contrast capable of achieving a first maximum density and a second development contrast capable of achieving a second maximum density from a relationship between N densities detected from the N toner patterns and N development contrasts set for forming the N toner patterns, respectively; determining a first image forming condition capable of achieving the first development contrast and a second image forming condition capable of achieving the second development contrast by referring to a plurality of image forming conditions capable of achieving a plurality of specific development contrasts that have been determined in advance, respectively; The image forming apparatus is configured as follows.

16. A photoconductor; a charging means for charging the photoconductor using a charging voltage; an exposure unit that irradiates the photoconductor with light of a set exposure amount to form an electrostatic latent image; a developing means for developing the electrostatic latent image with toner by using a developing voltage to form a toner image; a primary transfer means for transferring the toner image to an intermediate transfer body; a secondary transfer means for transferring the toner image from the intermediate transfer body to a sheet; a fixing means for fixing the toner image onto the sheet; an image reading means for reading a test image, which is the toner image fixed on the sheet; a conversion means for converting a reading result of the image reading means into a density; a determination unit for determining image forming conditions capable of achieving a plurality of different maximum densities based on the density, the image forming conditions including the charging voltage, the exposure amount, and the developing voltage; The test image includes N toner patterns formed by setting different development contrasts, The determining means is determining a first development contrast capable of achieving a first maximum density and a second development contrast capable of achieving a second maximum density from a relationship between N densities detected from the N toner patterns and N development contrasts set for forming the N toner patterns, respectively; determining a first image forming condition capable of achieving the first development contrast and a second image forming condition capable of achieving the second development contrast by referring to a plurality of image forming conditions capable of achieving a plurality of specific development contrasts that have been determined in advance, respectively; The image forming apparatus is configured as follows.

Images