JP2007163802A - Image forming device and image concentration control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce down time and amounts of consumed materials in an image forming device having various image forming modes in relative to a technology which adjusts the concentration and gradation each time changing the image forming modes. <P>SOLUTION: The image forming device includes an imaging forming section and a concentration controller. The imaging forming section forms images in either one of the various image forming modes different in their processing speed. The concentration controller applies either one of the image forming modes and controls the image concentration in the image forming section. Above all, the concentration controller makes concentration control in a first image forming mode in frequencies different from in a second image forming mode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

  In general, an image forming apparatus using an electrophotographic image forming process is likely to vary in image density depending on various conditions such as a use environment and the number of prints. In particular, in a color image forming apparatus that performs color printing by superposing a plurality of color toner images, when the image density of each color varies, the color balance (so-called color) varies.

Therefore, many of recent color image forming apparatuses detect the toner amount of a test image formed on an image carrier and control the image density according to the detection result (Patent Document 1).
JP-A-11-65237

  By the way, the image forming apparatus has a plurality of image forming modes having different process speeds. As these image forming modes, for example, there are a normal speed mode for performing standard printing, a low speed mode having a lower process speed than the normal speed mode, and the like. The low speed mode is used when printing an OHT (overhead transparency) sheet or cardboard.

  In general, when the image forming mode changes, the image density characteristic also changes. Therefore, in order to obtain a good color balance in all image forming modes, it is necessary to perform image density control for each image forming mode.

  However, when image density control is performed for all of many image forming modes, the time required for image density control becomes very long. That is, the time during which an image cannot be formed (downtime) increases, which is not preferable. In addition, consumables such as toner will be consumed more than necessary.

  Therefore, an object of the present invention is to solve at least one of such problems and other problems. Other issues can be understood throughout the specification.

  The image forming apparatus according to the present invention includes an image forming unit and a density control unit. The image forming unit forms an image in any of a plurality of image forming modes having different process speeds. The density control unit applies any one of the plurality of image forming modes to control the image density in the image forming unit. In particular, the density control unit makes the execution interval of the image density control under the first image forming mode different from the execution interval of the image density control under the second image forming mode.

  According to the present invention, the execution interval of image density control under the first image formation mode is different from the execution interval of image density control under the second image formation mode. That is, every time the image density control is not executed under all image forming modes, downtime is reduced. Further, the total toner consumption consumed by the image density control is reduced.

  An embodiment of the present invention is shown below. Of course, the individual embodiments described below will be helpful in understanding various concepts such as the superordinate concept, intermediate concept and subordinate concept of the present invention. Further, the technical scope of the present invention is determined by the scope of the claims, and is not limited by the following individual embodiments.

  FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment. The multicolor image forming apparatus 100 employs an electrophotographic system for the image forming unit 101.

  The recording material cassette 102 stores a plurality of recording materials P. The paper feed roller 103 picks up and feeds the recording material P from the recording material cassette 102 one by one. The fed recording material P is conveyed to the registration roller pair 104. Further, the recording material P is fed to the image forming unit 101 by the registration roller pair 104 at a predetermined timing.

  Note that the image forming unit 101 includes four image forming stations for forming images of developers of different colors on the recording material P. In this example, yellow, magenta, cyan, and black toners are used as developers.

  The photosensitive drum 105 is a kind of image carrier, and its surface is uniformly charged by a charging roller 106 that receives power from a high-voltage power supply circuit (FIG. 2). The exposure device 107 irradiates the surface of the photosensitive drum 105 with the light beam L. Thereby, an electrostatic latent image is formed on the surface of the photosensitive drum 105. Thus, the exposure apparatus 107 has a function of forming an electrostatic latent image.

  The developing roller 108 visualizes the electrostatic latent image using a developer such as toner and forms a toner image. The toner image on the photosensitive drum 105 is transferred to the recording material P by the transfer roller 109.

  An electrostatic adsorption conveyance belt (hereinafter referred to as ETB) 110 is interposed between the photosensitive drum 105 and the transfer roller 109. The ETB 110 is stretched between the drive roller 111 and the tension roller 112. The ETB 110 is rotated by the drive roller 111. The ETB 110 conveys the recording material P to each image forming station while adsorbing the recording material P. The ETB 110 functions as an image carrier during density adjustment and gradation adjustment.

  The recording material P onto which the toner images of different colors are sequentially transferred at each image forming station is conveyed to the fixing nip portion. The fixing nip portion includes a pressure roller 113 and a heating device 114. The unfixed toner image is heated and pressurized at the fixing nip portion and fixed on the recording material P. Thereafter, the recording material P is discharged out of the image forming apparatus 100 by a discharge roller 115.

  The density detection sensor 120 detects the density of the test image formed on the ETB 110. In density adjustment and gradation adjustment, the ETB 110 also functions as an image carrier that carries a test image. Note that the test image may be called a test patch, a patch pattern, a pattern image, a patch image, or the like.

  The image forming apparatus 100 includes a plurality of image forming modes having different process speeds. Such image forming modes include, for example, a normal speed mode and a low speed mode. The process speed in the normal speed mode is higher than the process speed in the low speed mode.

  The process speed in the normal speed mode is generally determined based on plain paper such as PPC (plain paper copy) paper that is most frequently used. On the other hand, the process speed in the low-speed mode is determined based on, for example, an OHT sheet or cardboard. This is because in the OHT sheet, it is preferable to reduce the fixing speed in order to improve the toner permeability.

  Further, since the heat capacity of the thick paper is larger than that of the plain paper, the thick paper needs more heat than the plain paper in order to fix the toner. Therefore, for thick paper, it is preferable to increase the amount of heat applied per unit time by slowing the fixing speed.

  For this reason, the process speed in the low speed mode is generally about 1/2 to 1/4 of the process speed in the normal speed mode. In the experiment described below, the process speed in the normal speed mode is 100 mm / sec, and the process speed in the low speed mode is 50 mm / sec.

  By the way, in an electrophotographic image forming apparatus, density characteristics and gradation characteristics fluctuate depending on environmental conditions such as temperature and humidity in which the apparatus is used and the degree of consumption of the image forming station. In order to correct this variation, image density control is required.

  The image forming apparatus 100 forms a test image of each color on the ETB 110 and reads it with the density detection sensor 120. The image forming apparatus 100 adjusts parameters (eg, process conditions and γ correction table) such as a charging bias corresponding to the density and an exposure light amount corresponding to the gradation based on the acquired density data. As a result, the maximum density characteristic and gradation characteristic of each color are optimized.

  FIG. 2 is a block diagram illustrating an example of a control unit according to the embodiment. The image forming controller 200 is a control unit for processing a job received from the PC 220. The engine controller 210 is a control unit that controls the image forming unit 101 and the like. Any controller can be composed of a CPU, RAM, ROM, ASIC, or the like.

  A raster image processor (RIP) 201 develops page description language data received from the PC 220 into a bitmap image in RGB format. The image processing unit 202 performs color matching processing and color separation processing on the bitmap image. The γ correction unit 203 executes γ correction on the CMYK format data output from the image processing unit. In general, it is known that the γ characteristic of the image forming unit 101 changes according to the environment in which the image forming apparatus 100 is used, the number of printed sheets, and the like. Therefore, a desired gradation can be obtained by γ correction. Note that the γ correction unit 203 performs γ correction using the γ correction table 205.

  The halftone processing unit 204 performs halftone processing such as halftone processing on the image data after γ correction. The image signal output from the halftone processing unit 204 is input to the exposure control circuit 211 in the engine controller 210. The exposure control unit 211 controls the amount of exposure light output from the exposure apparatus 107 according to the input image signal. In this way, the exposure device 107 forms an electrostatic latent image on the surface of the photosensitive drum 105.

  The control unit 212 comprehensively controls each unit of the engine controller 210 and each unit connected to the engine controller 210. According to the present embodiment, the control unit 212 changes the execution intervals of a plurality of image density control modes. The control unit 212 executes different image density control modes for the normal speed mode and the low speed mode.

  The storage unit 214 is a ROM or RAM for storing control programs and various data. The high voltage power supply circuit 215 applies a high voltage of several hundred volts to the charging roller 106 and the developing roller 108 based on the process conditions (charging conditions and developing conditions) determined by the image density control.

  The conveyance control circuit 216 drives the photosensitive drum 105 and the driving roller 111 according to the process speed designated by the control unit 212.

  FIG. 3 is a diagram for explaining an example of the concentration detection sensor according to the embodiment. Here, an optical sensor is employed as an example of the density detection sensor 120. A light emitting element 301 such as an LED and a light receiving element 302 such as a photodiode are attached to the housing 300. Light irradiated by the light emitting element 301 is incident on the measurement object B at an angle θ and is reflected by the measurement object B. The light receiving element 302 faces the measurement object B at an angle ψ, and detects both regular reflection light and diffuse reflection light from the measurement object B. Usually θ and ψ are equal, for example, 30 °.

  The detection principle of the test image with this optical sensor will be described. The light beam emitted from the light emitting element 301 is reflected by the ETB 110 serving as a base and detected by the light receiving element 302. When a test image is formed on the ETB 110, the background where the toner is present is hidden, and the amount of reflected light is reduced. Accordingly, the amount of reflected light gradually decreases as the amount of toner in the test image increases. Based on the relationship between the toner density and the amount of reflected light, the density of the test image can be obtained.

  FIG. 4 is a diagram illustrating the relationship between the output value from the density detection sensor 120 and the toner amount. The vertical axis represents the output value (voltage) of the concentration detection sensor 120. The horizontal axis represents the image forming density (corresponding to the toner amount). Note that the maximum output voltage of the concentration detection sensor 120 is assumed to be 5V.

  In FIG. 4, a curve A represents output characteristics when the density detection sensor 120 is not soiled and the ETB 110 is free from soiling and gloss reduction. On the other hand, the curve B shows the output characteristics when the density detection sensor 120 is dirty.

  Comparing the two, it can be understood that the output voltage is decreased as compared with the curve A. As described above, when the surface of the concentration detection sensor 120 or the ETB 110 becomes dirty, the output voltage decreases. Therefore, it is desirable to correct the output of the density detection sensor 120 using the output value (background output value) from the density detection sensor 120 obtained by detecting the ETB 110 in the absence of toner. Specifically, the output value related to the test image may be normalized with the background output value of the ETB 110 (the output value of density 0 in FIG. 4). The background output value is detected in the first round of the ETB 110, and the density of the test image is detected in the second round.

<Image density control>
Here, Dmax control and Dhalf control will be described as an example of image density control. The Dmax control is a process for adjusting process conditions such as a developing bias and a charging bias to a suitable state. Dhalf control is processing for adjusting the density gradation characteristics of an image to a suitable state. The Dhalf control is executed using the process conditions determined by the Dmax control.

<Dmax control>
FIG. 5 is a flowchart illustrating an example of Dmax control according to the embodiment. In step S <b> 501, the control unit 212 performs background measurement of the ETB 110 using the density detection sensor 120. Of course, no toner image is formed on the ETB 110. Note that the number of measurement positions and the number of measurement positions related to the background measurement are the same as the number of test image formation positions and the number of test images used for image density control.

  In step S <b> 502, the control unit 212 controls the image forming unit 101 to form a test image on the ETB 110. At this time, the control unit 212 reads out the image data of the test image from the storage unit 214 and sends it to the image forming controller 200.

  FIG. 6 is a diagram illustrating an example of a Dmax control test image formed on the ETB. On the ETB 110, three 8 mm square test images are formed at 12 mm intervals for each color. Therefore, a total of 12 test images are formed. The three test images for each color have different development biases. Note that a houndstooth pattern with a printing rate of 50% is used as the test image. As is well known, the houndstooth pattern is a pattern in which dots having a density of 100% and 0% are alternately repeated. The correspondence between each test image and the development bias is as follows. Ym1, Mm1, Cm1, Km1 = −210V. Ym2, Mm2, Cm2, Km2 = −260V. Ym3, Mm3, Cm3, Km3 = -310. That is, the control unit 212 sets these development biases in the high voltage power supply circuit 215.

  In step S <b> 503, the control unit 212 detects the amount of reflected light from the test image using the density detection sensor 212. In step S504, the control unit 212 converts the detected amount of reflected light into density data.

  For example, the control unit 212 divides the output value from the density detection sensor 120 for the test image by the background output value. Thereby, the output value from the density detection sensor 120 is normalized. Next, the control unit 212 converts the normalized output value (the amount of reflected light) into density data using a density conversion table stored in the storage unit 214.

  In step S505, the control unit 212 adjusts the process conditions based on the acquired density data. Here, only cyan density adjustment will be described, but magenta, yellow, and black are also adjusted in the same manner.

  FIG. 7 is a diagram showing the correspondence between density and development bias. The horizontal axis represents the development bias. The vertical axis represents density data detected by the density detection sensor 120. The plot in the figure represents density data for each test image of Cm1, Cm2, and Cm3. In this embodiment, as an example, the density target value for Dmax control is set to 0.6.

  Here, the control unit 212 compares the density data of each test image with the target density value, and calculates a developing bias for obtaining the target density value. According to FIG. 7, the target density value 0.6 is between Cm1 and Cm2. Therefore, the control unit 212 linearly interpolates between Cm1 and Cm2, and obtains the developing bias from a linear equation obtained by linear interpolation. In the example of FIG. 7, the developing bias is −240V.

  The above is the Dmax control according to the present embodiment. In this example, the developing bias is used as the process condition, but the present invention is not limited to this. For example, process conditions such as a charging bias and an exposure amount may be employed.

<Dhalf control>
FIG. 8 is a flowchart illustrating an example of Dhalf control according to the embodiment. In step S <b> 801, the control unit 212 performs background measurement of the ETB 110 using the concentration detection sensor 120. Of course, no toner image is formed on the ETB 110. Note that the number of measurement positions and the number of measurement positions related to the background measurement are the same as the number of test image formation positions and the number of test images used for image density control.

  In step S <b> 802, the control unit 212 controls the image forming unit 101 to form a test image on the ETB 110. At this time, the control unit 212 reads out the image data of the test image from the storage unit 214 and sends it to the image forming controller 200.

  FIG. 9 is a diagram illustrating an example of a test image for Dhalf control formed on the ETB. Corresponding to the position where the density detection sensor 120 is disposed, eight 8 mm square test images are formed at intervals of 2 mm for each color. Therefore, a total of 32 test images are formed. Further, the background measurement of the ETB 110 is executed at the positions where the 32 test images are formed.

  The control unit 212 forms eight test images having different printing rates (density gradation degrees) for each of Y, M, C, and K. The correspondence between each test image and the printing rate is as follows. Yh1, Mh1, Ch1, Kh1 = 12.5%. Yh2, Mh2, Ch2, Kh2 = 25%. Yh3, Mh3, Ch3, Kh3 = 37.5%. Yh4, Mh4, Ch4, Kh4 = 50%. Yh5, Mh5, Ch5, Kh5 = 62.5%. Yh6, Mh6, Ch6, Kh6 = 75%. Yh7, Mh7, Ch7, Kh7 = 87.5%. Yh8, Mh8, Ch8, Kh8 = 100%.

  In step S <b> 803, the control unit 212 detects the amount of reflected light from the test image using the density detection sensor 120. In step S804, the control unit 212 converts the detected amount of reflected light (output value from the density detection sensor 120) into density data. The conversion processing to density data is as described in step S504. In step S805, the control unit 212 executes gradation control (gradation adjustment) based on the acquired density data.

  FIG. 10 is a diagram for explaining an example of gradation adjustment according to the embodiment. Here, only cyan tone adjustment will be described, but tone adjustment is performed in the same manner for magenta, yellow, and black. In FIG. 10, the horizontal axis represents image data. The vertical axis represents density data detected by the density detection sensor 120. Each plot in the figure represents density data for each test image of Ch1, Ch2, Ch3, Ch4, Ch5, Ch6, Ch7, and Ch8.

  Here, the straight line T represents a target gradation characteristic for image density control. In the present embodiment, the target gradation characteristic T is determined so that the relationship between the image data and the density data is a proportional relationship. A curve γ represents a gradation characteristic in a state where gradation adjustment is not performed. The density data obtained from the test image is only Ch1, Ch2, Ch3, Ch4, Ch5, Ch6, Ch7, and Ch8. Therefore, the curve γ is obtained by performing spline interpolation on these density data.

  A curve D represents a gradation correction table (eg, γ correction table) calculated by this control. A γ correction table is calculated by obtaining a point that is symmetric with respect to the target gradation characteristic T from each point of the curve γ. The calculation of the γ correction table may be executed by either the control unit 212 or the γ correction unit 203. At the time of image formation, the γ correction unit 203 corrects image data using the γ correction table 205. Thereby, a target gradation characteristic is obtained.

<Execution control for multiple image density control modes>
As described above, the image forming apparatus 100 has two print modes, a normal speed mode for forming an image on plain paper and a low speed mode for forming an image on thick paper.

  By the way, according to the difference in process speed, dark attenuation and light attenuation in the photosensitive drum are different. Of course, the development characteristics are different. Therefore, it is preferable that the image density control is executed individually for each of the normal speed mode and the low speed mode.

  However, if image density control is executed for each image forming mode every time, downtime increases. Therefore, in this embodiment, the downtime and the toner consumption are reduced by making the execution interval of the image density control corresponding to each image forming mode different.

  FIG. 11 is a flowchart showing image density control according to the first embodiment. In step S1101, the control unit 212 determines whether it is time to execute image density control in the normal speed mode. The image density control mode executed in the normal speed mode is referred to as an image density control mode for plain paper. The image density control includes the above-described Dmax control and Dhalf control.

  FIG. 12 is a diagram showing the relationship between the number of images formed in the normal speed mode and the variation in gradation characteristics. ○ indicates that there is no problem in the gradation characteristics. Δ indicates that a slight problem occurs in the gradation characteristics. X indicates that a significant problem has occurred in the gradation characteristics. According to FIG. 12, it can be seen that there is a problem in the gradation characteristics when the number of formed images exceeds 150.

  FIG. 13 is a diagram showing the relationship between the number of images formed in the low-speed mode and the variation in gradation characteristics. According to FIG. 13, it can be seen that there is a problem in the gradation characteristics when the number of formed images is 250 to 300. Further, comparing FIG. 12 with FIG. 13, it can be seen that the gradation characteristics in the low speed mode are relatively more stable than the gradation characteristics in the normal speed mode. Therefore, the execution interval of the image density control in the low speed mode may be longer than the execution interval of the image density control in the normal speed mode.

  In the present embodiment, the execution timing of the image density control is executed when a change in gradation characteristics is expected. For example, the execution timing is as follows.

1. 1. When the image forming apparatus 100 is powered on 2. When the developing device or the photosensitive drum 105 is replaced. 3. When the period during which the image forming apparatus 100 is not used exceeds a predetermined threshold (eg, 6 hours). When the number of images formed reaches a predetermined threshold (eg, 100 sheets in the normal speed mode, 230 sheets in the low speed mode).

  The control unit 212 counts the number of image formations, and stores the counted number of image formations in the storage unit 214. It is assumed that the threshold value for each image forming mode is also stored in the storage unit 214. If it is not the execution timing as a result of the determination, the process proceeds to step S1103. On the other hand, at the execution timing, in step S1102, the control unit 212 executes image density control in the normal speed mode.

  In step S1103, the control unit 212 determines whether it is time to execute image density control in the low speed mode. The image density control mode executed in the low speed mode is referred to as an image density control mode for cardboard. As described above, the execution interval of the image density control executed in the low speed mode may be relatively longer than the execution interval of the image density control executed in the normal speed mode. This is because the execution interval of image density control executed in the normal speed mode must be relatively shorter than the execution interval of image density control executed in the low speed mode.

  As a result of the determination, if it is not the execution timing, the control unit 212 ends the image density control based on this flowchart. On the other hand, at the execution timing, in step S1104, the control unit 212 executes image density control in the low speed mode.

  According to this embodiment, the execution interval of the image density control under the normal speed mode is different from the execution interval of the image density control under the low speed operation mode. That is, since image density control is not executed every time under all image forming modes, downtime associated with image density control is reduced. Further, the total toner consumption consumed by the image density control is reduced as compared with the case where the image density control is executed every time under all image forming modes.

  Further, the process speed in the low speed mode is lower than the process speed in the normal speed mode. In this case, as shown in FIGS. 12 and 13, the image density characteristic under the low speed mode is more durable than the image density characteristic under the normal speed mode. Therefore, the control unit 212 can make the execution interval of the image density control under the low speed mode longer than the execution interval of the image density control under the normal speed mode. Thereby, downtime and toner consumption can be suitably reduced.

[Second Embodiment]
In the first embodiment, for image density control to be executed individually for each of a plurality of image forming modes, the downtime and the like are improved by making the execution interval different for each image forming mode. In the second embodiment, although image density control is executed in a certain image forming mode, even when image density control is not executed in another image forming mode, the latter color balance is suitably maintained. With the goal.

  By the way, the user may be able to designate the start of image density control execution for each image forming mode from an operation unit (not shown). For example, if the user changes the execution of the image density control from “possible” to “no”, the image density control is not executed at all until the user changes to “possible” next time. In this case, the image density control execution interval may be undesirably long. That is, the image forming conditions determined when the image density control was executed last time are continuously used. Of course, it goes without saying that the color balance shifts as the number of formed images increases.

  FIG. 14 is a flowchart showing image density control according to the second embodiment. In step S1401, the control unit 212 determines whether image density control has been executed under the normal speed mode.

  If it has been executed, the process advances to step S1402, and the control unit 212 selects the first table. This first table is used to determine the image forming condition for the normal speed mode from the result of the image density control executed in the normal speed mode. It is assumed that the first table is stored in the storage unit 214 in advance. The control unit 212 determines the image forming conditions for the normal speed mode based on the selected first table.

  In step S1403, the control unit 212 determines whether image density control has been executed under the low speed mode. If it has been executed, the process advances to step S1404 to select the third table. This third table is used for determining the image forming conditions for the low speed mode from the result of the image density control executed in the low speed mode. It is assumed that the third table is stored in the storage unit 214 in advance. The control unit 212 determines image forming conditions for the low speed mode based on the selected third table.

  On the other hand, if it is determined in step S1403 that the image density control is not performed in the low speed mode, the process proceeds to step S1410. In step S1410, the control unit 212 selects the fourth table. The fourth table is used to determine the image forming conditions for the low speed mode from the result of the image density control executed under the normal speed mode. It is assumed that the fourth table is also stored in the storage unit 214 in advance. The control unit 212 determines the image forming conditions for the low speed mode based on the selected fourth table.

  On the other hand, if it is determined in step S1401 that the image density control is not executed under the normal speed mode, the process proceeds to step S1420. In step S1420, the control unit 212 executes image density control under the low speed mode.

  In step S1421, the control unit 212 selects the second table and the third table. This second table is used to determine the image forming conditions for the normal speed mode from the result of the image density control executed in the low speed mode. It is assumed that the second table is also stored in the storage unit 214 in advance. The control unit 212 determines image forming conditions for the normal speed mode based on the selected second table. Further, the control unit 212 determines the image forming conditions for the low speed mode based on the selected third table.

  Note that the second and fourth tables are tables for predicting or estimating the image forming conditions for the other image forming mode from the execution result of the image density control under the one image forming mode. Therefore, the accuracy of control may be lower than when the first and third tables are used. However, even if the image density control execution interval under a specific image forming mode becomes inappropriately long, the color balance and the like can be suitably maintained to some extent. However, it is desirable that the image density control under at least one image forming mode is executed periodically.

  According to the second embodiment, even when the execution interval of image density control under a specific image forming mode becomes inappropriately long, color balance and the like can be suitably maintained. In other words, the color balance under a specific image forming mode can be suitably maintained by using the execution result of the image density control under another image forming mode that is appropriately executed.

[Other Embodiments]
You may combine the concept of 1st Embodiment mentioned above and the concept of 2nd Embodiment in the range which does not contradict. For example, in step S1102, the control unit 212 may select the fourth table in order to determine the image forming conditions for the low speed mode. In step S1104, the control unit 212 may select the second table in order to determine the image forming conditions for the normal speed mode. In this way, the execution interval of image density control under each image forming mode can be made longer than each execution interval in the first embodiment.

  Note that the present invention does not depend on the image forming method. For example, the present invention can be applied to an image forming apparatus using an intermediate transfer member. The present invention can also be suitably applied to an image forming apparatus that forms a color image using a single photosensitive drum (image carrier).

1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment. It is a block diagram which shows an example of the control part which concerns on embodiment. It is a figure for demonstrating an example of the density | concentration detection sensor which concerns on embodiment. FIG. 4 is a diagram illustrating a relationship between an output value from a density detection sensor 120 and a toner amount. It is a flowchart which shows an example of Dhalf control which concerns on embodiment. It is a figure which shows an example of the test image for Dmax control formed on ETB. FIG. 6 is a diagram illustrating a correspondence relationship between density and development bias. It is a flowchart which shows an example of Dhalf control which concerns on embodiment. It is a figure which shows an example of the test image for Dhalf control formed on ETB. It is a figure for demonstrating an example of the gradation adjustment which concerns on embodiment. 5 is a flowchart illustrating image density control according to the first embodiment. It is a figure which shows the relationship between the image formation number in normal speed mode, and the fluctuation | variation of a gradation characteristic. It is a figure which shows the relationship between the image formation number in low speed mode, and the fluctuation | variation of a gradation characteristic. It is a flowchart which shows the image density control which concerns on 2nd Embodiment.

Claims (6)

An image forming unit that forms an image in any of a plurality of image forming modes having different process speeds;
A density control unit that applies any one of the plurality of image forming modes and executes image density control in the image forming unit;
The density control unit is configured such that, among the plurality of image forming modes, the execution interval of the image density control under the first image forming mode is different from the execution interval of the image density control under the second image forming mode. An image forming apparatus characterized by comprising:   When the process speed of the second image forming mode is lower than the process speed of the first image forming mode, the density control unit performs the image density control execution interval under the second image forming mode. The image forming apparatus according to claim 1, wherein the image forming apparatus is set to be longer than an execution interval of the image density control in the first image forming mode.   When the image density control is executed under the first image forming mode, the density control unit is configured to perform an image for the second image forming mode that has not been executed based on the result of the image density control. The image forming apparatus according to claim 1, wherein a forming condition is determined. A first table and a second table for determining image forming conditions used in the first image forming mode, and a third table for determining image forming conditions used in the second image forming mode. A storage unit for storing the table and the fourth table;
When the image density control is executed under the first image forming mode, the first table and the fourth table are selected, and the image density control is executed under the second image forming mode. And a selection unit for selecting the second table and the third table.
The first table is a table for determining an image forming condition for the first image forming mode from a result of the image density control acquired under the first image forming mode. The table is a table for determining image forming conditions for the first image forming mode from the result of the image density control acquired under the second image forming mode, and the third table is , A table for determining an image forming condition for the second image forming mode from a result of the image density control acquired under the second image forming mode, and the fourth table is the first table. 4. The image form according to claim 3, wherein the image shape is a table for determining an image forming condition for the second image forming mode from a result of the image density control acquired under one image forming mode. Apparatus. An image carrier for carrying an image;
A density detecting unit that detects the density of the test image formed on the image carrier by the image forming unit;
The image forming apparatus according to claim 1, wherein the density control unit executes the image density control according to density data of the detected test image. Forming an image in any of a plurality of image forming modes having different process speeds;
Applying one of the plurality of image forming modes to perform image density control,
The image density control execution interval under the first image formation mode is different from the image density control execution interval under the second image formation mode among the plurality of image formation modes. Concentration control method.

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