JP3729023B2 - Image forming apparatus and image forming method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus and an image forming method for forming different color toner images and forming a color image by superimposing the multiple color toner images.
[0002]
[Prior art]
In this type of image forming apparatus, the image density may change due to fatigue and aging of the photoconductor and toner, changes in temperature and humidity around the apparatus, and the like. Therefore, many techniques have been proposed for stabilizing the image density by appropriately adjusting density control factors that affect the image density of the toner image, such as a charging bias, a developing bias, and an exposure amount. For example, in the invention described in Japanese Patent Application Laid-Open No. 11-84855, image density is stabilized by appropriately adjusting the developing bias. That is, in this prior art, patch images are formed on the intermediate transfer member while changing the developing bias, and the image density of each patch is detected. Based on these detection values, an optimum developing bias is determined, and the toner image density is adjusted.
[0003]
The patch image pattern used at this time includes a first yellow patch image, a first magenta patch image, a first cyan patch image, a first black patch image, a second yellow patch image from the image writing position. The second magenta patch image, the second cyan patch image, the second black patch image,... Are formed in this order. As a specific patch creation procedure, first, first, second,... Yellow patch images are formed on the intermediate transfer member while changing the developing bias. Thereafter, a magenta patch image, a cyan patch image, and a black patch image are sequentially formed. When the creation of all the patch images is completed, the image density of these patch images is collectively detected.
[0004]
[Problems to be solved by the invention]
By the way, when the patch preparation conditions (development bias in the above-described conventional example) are changed as described above, the fog generation conditions in which fog and background stains (hereinafter simply referred to as “fogging”) occur may be set. . In particular, when it is necessary to change the patch creation condition over a relatively wide range, the patch creation condition is set as the fog generation condition, and the possibility of occurrence of fog increases.
[0005]
If the patch creation condition is set as the fog generation condition in this manner, the image base portion is stained until the next patch creation condition is changed, and the density adjustment of the toner image cannot be performed with high accuracy. For example, when the development bias is changed and set to form the second yellow patch image after the first yellow patch image is created, if the changed development bias enters the fog generation condition, The magenta patch image, the first cyan patch image, and the first black patch image are soiled. Therefore, the first magenta patch image, the first cyan patch image, and the first black patch image are formed in the fog portion after the yellow patch image, and the density of the patch images of other toner colors is accurately set. It cannot be detected.
[0006]
The present invention has been made in view of the above problems, and for each toner color, an image that can determine the optimum value of the density control factor required for adjusting the image density of the toner image to the target density with high accuracy. An object of the present invention is to provide a forming apparatus and an image forming method.
[0007]
[Means for Solving the Problems]
  An image forming apparatus according to the present invention is an image forming apparatus that forms toner images of different colors and superimposes the toner images of multiple colors to form a color image. An image carrier that carries an image, and density detection means that detects an image density of a patch image formed on the image carrier;A control means capable of changing and setting the concentration control factor within a predetermined variable band, and setting the range for changing the concentration control factor within the variable band in two steps, a wide range and a narrow range;It has.The control means executes the following first patch density detection process for each color while gradually changing the density control factor at a first interval within a wide range, and also detects the first patch density detection. Based on the image density detected by the process, after obtaining the value of the density control factor necessary for adjusting the image density of the toner image of each color to the target density as a provisional value, the following second patch density detection process is executed. At the same time, based on the image density detected by the second patch density detection process, the optimum value of the density control factor necessary for adjusting the image density of each color toner image to the target density is determined.Here, in the first patch density detection process, a plurality of toner images are formed on the image carrier as patch images while changing a density control factor that affects the image density of the toner image. The plurality of patch images are cleaned and removed from the image carrier.In the second patch density detection process, a plurality of toner images are patched onto the image carrier while gradually changing density control factors within a narrow range including the provisional value for all toner colors. After the formation, the density of each patch image is collectively detected by the density detecting means.
[0008]
  The image forming method according to the present invention is an image forming method in which a plurality of different color toner images are formed, and a color image is formed by superimposing the plurality of color toner images, in order to achieve the above object. Necessary for adjusting the image density of the toner image to the target density based on the first step of executing the first patch density detection process for each color and the image density detected by the first patch density detection process Concentration control factorsTemporarily find the valueAnd the second stepThe third step of executing the second patch density detection process and the density necessary for adjusting the image density of each color toner image to the target density based on the image density detected by the second patch density detection process A fourth step of determining an optimum value of the control factor;It has.
[0009]
In these inventions, for each toner color, creation of a patch image on the image carrier, detection of the density of the patch image, and cleaning removal of the patch image from the image carrier are performed in this order. Therefore, even if fog occurs at the time of creating the patch image, the image carrier is cleaned before creating the patch image for the next toner color, and the influence of fog is completely eliminated. That is, a patch image is created on an image carrier that is always free of dirt for each toner color.
[0010]
By the way, when the optimum value of the density control factor is determined as described above, it is slightly different from the actual color image forming procedure. That is, the procedure for determining the optimum value of the density control factor described above involves creating patch images for each color and removing the cleaning. By continuously forming toner images of the respective toner colors, the color images can be obtained by superimposing them. This is different from the actual image forming procedure for obtaining an image. Therefore, in order to obtain an optimum value with higher accuracy, the optimum value of the density control factor is provisionally obtained as described above, and the second patch density detection process is executed and detected by the second patch density detection process. Based on the obtained image density, the optimum value of the density control factor necessary for adjusting the image density of each color toner image to the target density may be finally obtained to match the actual color image forming procedure. . Here, in the second patch density detection process, a plurality of toner images are patched onto the image carrier while changing density control factors stepwise within a narrow range including the provisional value for all toner colors. After the formation, the density of each patch image is collectively detected by the density detecting means.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
A. Overall configuration of image forming apparatus
FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This image forming apparatus forms a full color image by superposing four color toners of yellow (Y), cyan (C), magenta (M), and black (K), or uses only black (K) toner. This is an apparatus for forming a monochrome image. In this image forming apparatus, when an image signal is given to the main controller 11 of the control unit 1 from an external device such as a host computer, the engine controller 12 controls each part of the engine unit E in response to a command from the main controller 11. Thus, an image corresponding to the image signal is formed on the sheet S.
[0012]
In the engine unit E, a toner image can be formed on the photosensitive member 21 of the process unit 2. That is, the process unit 2 includes a photosensitive member 21 that can rotate in the direction of the arrow in FIG. Developing units 23Y, 23C, 23M, and 23K, and a cleaning unit 24 are respectively disposed. The charging roller 22 is applied with a high voltage from the charging bias generator 121 and contacts the outer peripheral surface of the photoconductor 21 to uniformly charge the outer peripheral surface.
[0013]
Then, laser light L is irradiated from the exposure unit 3 toward the outer peripheral surface of the photosensitive member 21 charged by the charging roller 22. As shown in FIG. 2, the exposure unit 3 is electrically connected to an image signal switching unit 122, and a laser beam L is applied to the photosensitive member 21 in accordance with an image signal given through the image signal switching unit 122. An electrostatic latent image corresponding to the image signal is formed on the photosensitive member 21 by scanning exposure. For example, based on a command from the CPU 123 of the engine controller 12, when the image signal switching unit 122 is in conduction with the patch creation module 124, a patch image signal output from the patch creation module 124 is given to the exposure unit 3. Thus, a patch latent image is formed. On the other hand, when the image signal switching unit 122 is electrically connected to the CPU 111 of the main controller 11, the laser beam L is applied to the photosensitive member 21 in accordance with an image signal supplied from an external device such as a host computer via the interface 112. Then, an electrostatic latent image corresponding to the image signal is formed on the photosensitive member 21 by scanning exposure.
[0014]
The electrostatic latent image thus formed is developed with toner by the developing unit 23. That is, in this embodiment, as the developing unit 23, a yellow developing unit 23Y, a cyan developing unit 23C, a magenta developing unit 23M, and a black developing unit 23K are arranged along the photoconductor 21 in this order. Has been. These developing units 23Y, 23C, 23M, and 23K are configured so as to be able to come into contact with and separate from the photosensitive member 21, and in response to a command from the engine controller 12, the four developing units 23Y, 23M, 23C, One of the developing devices 23B selectively contacts the photoconductor 21, and a high voltage is applied by the developing bias generator 125 to apply toner of the selected color to the surface of the photoconductor 21 to thereby provide the photoconductor. The electrostatic latent image on 21 is revealed. Here, as a voltage to be applied to each developing device, a DC voltage may be simply applied, or an AC voltage may be superimposed.
[0015]
The toner image developed by the developing unit 23 is primarily transferred onto the intermediate transfer belt 41 of the transfer unit 4 in the primary transfer region R1 located between the black developing device 23K and the cleaning unit 24. The structure of the transfer unit 4 will be described in detail later.
[0016]
A cleaning unit 24 is disposed at a position advanced in the circumferential direction (in the direction of the arrow in FIG. 1) from the primary transfer region R1, and scrapes off toner remaining on the outer peripheral surface of the photoreceptor 21 after the primary transfer. Drop it.
[0017]
Next, the configuration of the transfer unit 4 will be described. In this embodiment, the transfer unit 4 includes rollers 42 to 47, an intermediate transfer belt 41 stretched over the rollers 42 to 47, and an intermediate toner image transferred to the intermediate transfer belt 41 on the sheet S. And a secondary transfer roller 48 for next transfer. A primary transfer voltage is applied to the intermediate transfer belt 41 from a transfer bias generator 126. When a color image is transferred onto the sheet S, the color toner images formed on the photosensitive member 21 are superimposed on the intermediate transfer belt 41 to form a color image, and the paper supply / discharge unit 6 supplies the color image. The sheet S is taken out from the cassette 61, the manual feed tray 62, or an additional cassette (not shown) by the paper portion 63 and conveyed to the secondary transfer region R2. Then, a color image is secondarily transferred to the sheet S to obtain a full color image. When a monochrome image is transferred to the sheet S, only the black toner image is formed on the intermediate transfer belt 41 on the photosensitive member 21, and is conveyed to the secondary transfer region R2 as in the case of a color image. Transfer to the sheet S to obtain a monochrome image.
[0018]
Note that the toner remaining on the outer peripheral surface of the intermediate transfer belt 41 after the secondary transfer is removed by the belt cleaner 49. The belt cleaner 49 is disposed so as to face the roller 46 with the intermediate transfer belt 41 interposed therebetween, and the cleaner blade comes into contact with the intermediate transfer belt 41 at an appropriate timing and remains attached to the outer peripheral surface thereof. Scrape off the toner.
[0019]
Further, a patch sensor PS (density detecting means) for detecting the density of the patch image formed on the outer peripheral surface of the intermediate transfer belt 41 as described later is disposed in the vicinity of the roller 43, and the intermediate transfer. A synchronization reading sensor RS for detecting the reference position of the belt 41 is disposed.
[0020]
Returning to FIG. 1, the description of the configuration of the engine unit E will be continued. The sheet S on which the toner image has been transferred by the transfer unit 4 is disposed on the downstream side of the secondary transfer region R2 along a predetermined paper feed path (two-dot chain line) by the paper feed unit 63 of the paper feed / discharge unit 6. The toner image on the sheet S conveyed to the fixing unit 5 is fixed on the sheet S. Then, the sheet S is further conveyed to the paper discharge unit 64 along the paper feed path 630.
[0021]
The paper discharge unit 64 has two paper discharge paths 641a and 641b. One paper discharge path 641a extends from the fixing unit 5 to the standard paper discharge tray, and the other paper discharge path 641b is a paper discharge path 641a. Substantially parallel to the paper feed portion 66 and the multi-bin unit. Three pairs of rollers 642 to 644 are provided along these paper discharge paths 641a and 641b, and the fixed sheet S is discharged toward the standard paper discharge tray or the multibin unit side, or the other side. In addition, the sheet is conveyed to the refeed unit 66 side in order to form an image.
[0022]
As shown in FIG. 1, the refeed unit 66 feeds the sheet S reversely conveyed from the paper discharge unit 64 as described above along the refeed path 664 (two-dot chain line). The sheet is conveyed to the gate roller pair 637 and is composed of three refeed roller pairs 661 to 663 arranged along the refeed path 664. In this manner, the sheet S conveyed from the paper discharge unit 64 is returned to the gate roller pair 637 along the refeed path 664 so that the non-image forming surface of the sheet S moves the intermediate transfer belt 41 in the paper supply unit 63. The image can be secondarily transferred to the surface.
[0023]
In FIG. 2, reference numeral 113 denotes an image memory provided in the main controller 11 for storing an image given from an external device such as a host computer via the interface 112, and reference numeral 127 controls the engine unit E. Is a RAM for temporarily storing control data to be executed, a calculation result in the CPU 123, and the like, and a reference numeral 128 is a ROM for storing a calculation program executed by the CPU 123.
[0024]
B. Density adjustment operation in image forming apparatus
Next, an image density adjustment operation in the image forming apparatus configured as described above will be described.
[0025]
B-1. First embodiment
FIG. 3 is a flowchart showing the density adjustment operation in the image forming apparatus of FIG. In this image forming apparatus, as shown in the figure, it is determined in step S1 whether or not it is necessary to update and set the developing bias and the charging bias by executing a density adjustment operation. For example, the bias setting may be started when an image can be formed after the main power supply of the image forming apparatus main body is turned on. Further, the continuous use time may be measured by a timer (not shown) provided in the apparatus main body, and the bias setting may be started every several hours.
[0026]
When “YES” is determined in step S1 and the bias setting is started, steps S2 and S3 are executed to calculate the optimum developing bias and set it as the developing bias (step S4). Subsequently, step S5 is executed to calculate the optimum charging bias and set it as the charging bias (step S6). In this way, the development bias and the charging bias are optimized. Hereinafter, the contents of the development bias calculation process (step S3) and the charging bias calculation process (step S5) will be described in detail.
[0027]
FIG. 4 is a flowchart showing the contents of the developing bias calculation process according to the first embodiment. FIG. 5 is a schematic diagram showing the processing contents of FIG. In this development bias calculation process (step S3), the color for creating the patch image is set to the first color, for example, yellow (step S31). Then, the developing bias is set in four stages within the predetermined range with the charging bias set in advance in step S2 (step S32). For example, in this embodiment, the entire variable band (Vb01 to Vb10) of the developing bias that can be supplied to the developing unit 23 by the developing bias generator 125 is set as a wide range, and 4 of the wide range (Vb01 to Vb10) are set. Points Vb01, Vb04, Vb07, and Vb10 are set as development biases.
[0028]
With such a bias setting, four yellow solid images (FIG. 6) are sequentially formed on the photosensitive member 21, and as shown in FIG. 7A, these images are formed on the intermediate transfer belt 41 in a predetermined arrangement order. The yellow patch image PI1 (Y) is transferred to the outer peripheral surface to form a first patch image (step S33). Here, in this embodiment, the yellow patch images PI1 (Y) are arranged on the intermediate transfer belt 41 functioning as the image carrier of the present invention at a relatively wide interval, thereby ensuring a stable time for bias switching. ing. Therefore, each patch image can be reliably formed with the set bias set in step S32.
[0029]
Each yellow patch image PI1 (Y) transferred to the intermediate transfer belt 41 passes through the patch sensor PS as the intermediate transfer belt 41 rotates, and the image density of the yellow patch image PI1 (Y) is adjusted by the patch sensor PS. Measurement is performed (step S34). When each yellow patch image PI1 (Y) passes through the patch sensor PS and moves to the belt cleaner 49, the yellow cleaner image PI1 (Y) on the intermediate transfer belt 41 is removed by cleaning by the belt cleaner 49. (Step S34). As described above, in this embodiment, while the intermediate transfer belt 41 is rotated once, patch image formation, image density measurement, and cleaning removal are continuously performed for each yellow patch image PI1 (Y). Yes. Of course, the patch image formation, the image density measurement, and the cleaning removal may be performed for each yellow patch image PI1 (Y) while the intermediate transfer belt 41 is rotationally moved over one turn. This also applies to “bias calculation processing in a wide range” described later.
[0030]
In the next step S35, it is determined whether or not patch images have been generated for all patch generation colors. While it is determined “NO”, the patch generation color is set to the next color (step S36). By repeating S32 to S34, as shown in FIGS. 7B to 7D, patch image formation, image density measurement, and cleaning are performed in the order of cyan (C), magenta (M), and black (K). Removal is performed continuously.
[0031]
On the other hand, if “YES” is determined in the step S35, a developing bias corresponding to the target density is obtained (step S37), and this is temporarily stored in the RAM 127 as the optimum developing bias. Here, when the measurement result (image density) matches the target density, the development bias corresponding to the image density may be set as the optimum development bias. As shown in FIG. 4, the optimum developing bias can be obtained by linear interpolation or averaging processing based on data D (Vb04) and D (Vb07) sandwiching the target density.
[0032]
Returning to FIG. 3, the optimum developing bias calculated as described above is read from the RAM 127 and set as the developing bias (step S4). Subsequently, an optimum charging bias is calculated (step S5) and set as a charging bias (step S6). Hereinafter, the charging bias calculation process (step S5) will be described in detail with reference to FIGS.
[0033]
FIG. 8 is a flowchart showing the contents of the charging bias calculation process according to the first embodiment. In this charging bias calculation process (step S5), the color for creating the patch image is set to the first color, for example, yellow (step S51). Then, the charging bias is set in four stages within a predetermined range including the predetermined value set in advance in step S2 or the immediately preceding optimum charging bias (step S52). For example, when the predetermined value or the immediately preceding optimum charging bias is between charging biases Va05 and Va06 as shown in FIG. 9A, four points Va04, Va05, Va06, and Va07 are set as charging biases.
[0034]
When four types of charging bias are set for the yellow color as described above, each yellow halftone image (FIG. 10) is formed on the photoconductor 21 while the charging bias is gradually increased from the lowest value Va04. These are sequentially formed and transferred to the outer peripheral surface of the intermediate transfer belt 41 to form a yellow patch image PI2 (Y) as a second patch image (FIG. 11A: step S53).
[0035]
In the next step S54, it is determined whether or not the second patch image has been generated for all the patch generation colors, and while it is determined “NO”, the patch generation color is set to the next color (step S55). Steps S52 and S53 are repeated, and the second patch is formed on the outer peripheral surface of the intermediate transfer belt 41 in the order of cyan (C), magenta (M), and black (K) as shown in FIGS. 11 (b) to 11 (d). Images PI2 (C), PI2 (M), and PI2 (K) are further formed.
[0036]
On the other hand, if “YES” is determined in the step S54, the image density of 16 (= 4 types × 4 colors) patch images PI2 (Y), PI2 (C), PI2 (M), PI2 (K) is determined by the patch sensor. Measurement is performed collectively with PS (step S56). The patch images PI2 (Y), PI2 (C), PI2 (M), and PI2 (K) thus measured for density are cleaned and removed by the belt cleaner 49.
[0037]
Subsequently, in step S57, a charging bias corresponding to the target density is obtained. Here, if the measurement result (image density) matches the target density, the charging bias corresponding to the image density may be set as the optimum charging bias. As shown in FIG. 5, the optimum charging bias can be obtained by linear interpolation based on data D (Va05) and D (Va06) sandwiching the target density.
[0038]
When the optimum charging bias is obtained for all the patch creation colors, the process proceeds to step S6 in FIG. 3, and the optimum charging bias obtained as described above is stored in the RAM 127, and from the RAM 127 in the normal image forming process. Set as readout and charging bias.
[0039]
As described above, in this embodiment, in calculating the optimum developing bias, a patch image is created on the intermediate transfer belt (image carrier) 41 for each toner color (step S32), and the density detection of the patch image ( Step S34) and cleaning removal of the patch image from the intermediate transfer belt 41 (step S34) are performed in this order. As described above, since the first patch density detection process including patch image creation, patch image density detection, and cleaning removal is performed for each toner color, fogging is performed when a patch image of a certain toner color is created. Even if this occurs, the intermediate transfer belt 41 is cleaned by the belt cleaner 49 before creating a patch image for the next toner color, and the influence of fog is completely eliminated. Therefore, a patch image is always created on the intermediate transfer belt 41 that is free of contamination for each toner color, and the optimum developing bias can be determined with high accuracy.
[0040]
In this embodiment, in calculating the optimum charging bias, as shown in FIG. 11, patch images PI2 (Y), PI2 (C), PI2 (M), and PI2 (K) of all toner colors are used. After the image is created on the intermediate transfer belt 41, the image density of each patch image PI2 (Y), PI2 (C), PI2 (M), PI2 (K) is measured. Similarly, a patch image is created on the intermediate transfer belt (image carrier) 41 for each toner color (step S53), the density of the patch image is detected (step S56), and the patch image from the intermediate transfer belt 41 is cleaned. The removal may be performed in this order.
[0041]
However, in this embodiment, continuous creation of patch images and batch measurement of image density are performed in the charging bias calculation process for the following reasons. The first reason is that the charging bias calculation process is executed after setting the developing bias to the optimum developing bias obtained in step S3 as described above (step S4). This is because the possibility of occurrence is low. The second reason is that when a color image is actually formed, only the first toner color (yellow in this embodiment) is transferred to the cleaned intermediate transfer belt 41, but the remaining toner colors are already transferred to the intermediate transfer belt. The toner image is transferred to the intermediate transfer belt 41 with another color toner image remaining on the toner image 41. Therefore, it is preferable to obtain the charging bias in a state close to the actual image forming procedure.
[0042]
B-2. Second embodiment
By the way, in an actual image forming apparatus, the state of the engine unit E varies greatly depending on the operation state of the apparatus. For example, while the image forming process is continuously executed, the state change of the engine unit E is relatively small, but the possibility that the state of the engine unit E is largely changed when the power is turned on is relatively high. .
[0043]
Therefore, if the density adjustment can be performed in the processing mode according to the state, the density adjustment can be performed efficiently and with high accuracy. For example, the optimum charging bias and the optimum developing bias change according to fatigue and change with time of the photoreceptor and toner, but the changes have a certain degree of continuity. Therefore, when the density adjustment is repeatedly performed, the density adjustment can be performed with higher accuracy if the density adjustment is performed based on the density control factor obtained by the previous density adjustment. On the other hand, when the power is turned on, it is difficult to predict the state of the engine unit, and it is necessary to change the concentration control factor within a relatively wide range to determine the optimum value.
[0044]
Therefore, in the second embodiment, basically, as in the first embodiment, the development bias calculation process is performed to obtain the optimum development bias, which is set as the development bias, and the charging bias calculation process is performed. Although the optimum charging bias is obtained, the development bias processing and the charging bias processing different from the first embodiment are executed in consideration of the above points. Each will be described in detail below.
[0045]
B-2-1. Development bias calculation processing
FIG. 12 is a flowchart showing the contents of the developing bias calculation process according to the second embodiment. In this development bias calculation process (step S3), first, one of the first and second process modes is selected as a process mode according to the operation status of the apparatus (step S301). In the first processing mode, as will be described later, the development bias is changed within a wide range (the entire development bias variable region) to obtain a provisional value of the optimum development bias. Further, based on the provisional value, a narrow range (about 1 / 3) determines the optimum developing bias while changing the developing bias, and is suitable when the state of the engine unit E cannot be predicted. On the other hand, in the second processing mode, as will be described later, the optimum developing bias is determined while changing the developing bias within a narrow range (about 1/3 of the variable region) including the previous optimum developing bias. This is suitable when there is little change in the state of the part E. In this embodiment, the specific selection determination in step S301 is performed based on the following criteria.
[0046]
(1) At power-on → 1st processing mode
When the power is turned on, the state of the engine unit E cannot be predicted at all, so the optimum developing bias is determined while changing the developing bias in the entire developing bias variable region.
[0047]
(2) When returning from sleep and the sleep time is less than the predetermined time → the second processing mode
In the case of returning from sleep, the state of the engine unit E may have changed greatly. However, if the sleep time is short, it is estimated that the state of the engine unit E is small, so the previous optimum development The optimum developing bias is determined while changing the developing bias within a narrow range including the bias (about 1/3 of the variable region).
[0048]
(3) When returning from sleep and the fixing temperature of the fixing unit 5 is equal to or higher than a predetermined temperature → second processing mode
In the case of returning from sleep, the state of the engine unit E may have changed greatly. However, if the fixing device that is a heat source in the fixing unit 5 is kept at a high temperature, the state of the engine unit E Since it is estimated that the change is small, the optimum developing bias is determined while changing the developing bias within a narrow range (about 1/3 of the variable region) including the previous optimum developing bias.
[0049]
(4) When returning from sleep (except cases (2) and (3) above) → First processing mode
Other than the above (2) and (3), the state of the engine unit E may have changed significantly when returning from sleep. Therefore, the optimum development is performed while changing the development bias in the entire development bias variable region. Determine the bias.
[0050]
(5) During continuous image formation → Second processing mode
When image formation is continuously performed, it is unlikely that the state of the engine unit E will change significantly from the previous density adjustment, so a narrow range including the previous optimum development bias (about 1/3 of the variable region). The optimum developing bias is determined while changing the developing bias in ().
[0051]
When the first processing mode is selected based on the above criteria, the first development bias calculation process (steps S311 to S313, S302) is executed to determine the optimum development bias, while the second processing mode is selected. Is selected, the second developing bias calculation process (steps S321, S322, S302) is executed to determine the optimum developing bias. In the following, description will be given separately.
[0052]
B-2-1-1. First developing bias calculation process (first processing mode)
In the first developing bias calculation process, as shown in FIG. 12, patch images for all colors (in this embodiment, four colors of yellow (Y), cyan (C), magenta (M), and black (K)) are used. (Step S311), the process proceeds to step S312 to form a plurality of patch images while gradually changing the developing bias in a relatively wide range and at relatively wide intervals. Based on the density of each patch image, a development bias necessary to obtain an optimum image density is provisionally obtained. The processing contents will be described in detail with reference to FIGS. 13 and 14.
[0053]
FIG. 13 is a flowchart showing the contents of the bias calculation process in the wide range of FIG. FIG. 14 is a schematic diagram showing the processing content of FIG. 13 and the content of bias calculation processing in a narrow range, which will be described later. In this calculation process, the color for creating the first patch image is set to the first color, for example, yellow (step S312a). Then, the developing bias is set in four stages at a relatively wide interval (first interval) within a wide range with the charging bias set in advance in step S2 (step S312b). For example, in this embodiment, the entire developing bias variable band (Vb01 to Vb10) that can be supplied to the developing unit 23 by the developing bias generator 125 is set as a wide range, and 4 of the wide ranges (Vb01 to Vb10) are set. Points Vb01, Vb04, Vb07, and Vb10 are set as development biases. Thus, in this embodiment, the first interval W1 is
W1 = Vb10−Vb07 = Vb07−Vb04 = Vb04−Vb01
It is said.
[0054]
With such a bias setting, four yellow solid images (FIG. 6) are sequentially formed on the photosensitive member 21, and as shown in FIG. 7A, these images are formed on the intermediate transfer belt 41 in a predetermined arrangement order. The yellow patch image PI1 (Y) is transferred to the outer peripheral surface to form the first patch image (step S312c). Here, in this embodiment, the yellow patch images PI1 (Y) are arranged on the intermediate transfer belt 41 functioning as the image carrier of the present invention at a relatively wide interval, thereby ensuring a stable time for bias switching. ing. Therefore, each patch image can be reliably formed with the set bias set in step S32.
[0055]
Each yellow patch image PI1 (Y) transferred to the intermediate transfer belt 41 passes through the patch sensor PS as the intermediate transfer belt 41 rotates, and the image density of the yellow patch image PI1 (Y) is adjusted by the patch sensor PS. Measurement is performed (step S312d). When each yellow patch image PI1 (Y) passes through the patch sensor PS and moves to the belt cleaner 49, the yellow cleaner image PI1 (Y) on the intermediate transfer belt 41 is removed by cleaning by the belt cleaner 49. (Step S312d). As described above, in this embodiment, while the intermediate transfer belt 41 is rotated once, patch image formation, image density measurement, and cleaning removal are continuously performed for each yellow patch image PI1 (Y). Yes.
[0056]
In the next step S312e, it is determined whether or not patch images have been generated for all patch generation colors. While it is determined “NO”, the patch generation color is set to the next color (step S312f). By repeating S312b to S312d, as shown in FIGS. 7B to 7D, patch image formation, image density measurement, and cleaning are performed in the order of cyan (C), magenta (M), and black (K). Removal is performed continuously.
[0057]
On the other hand, if “YES” is determined in the step S312e, a developing bias corresponding to the target density is obtained, and this is temporarily stored in the RAM 127 as a temporary bias. Here, when the measurement result (image density) matches the target density, the development bias corresponding to the image density may be a provisional bias, and when they do not match, the result is shown in FIG. As shown, the provisional bias can be obtained by linear interpolation or averaging processing based on data D (Vb04) and D (Vb07) sandwiching the target density.
[0058]
When the provisional bias is obtained in this way, the bias calculation process (1) in the narrow range of FIG. 12 is executed. FIG. 15 is a flowchart showing the contents of the bias calculation process (1) in the narrow range of FIG. In this calculation process, as in the previous calculation process (step S312), the color for creating the patch image is set to the first color, for example, yellow (step S313a). Then, the developing bias is set in four stages at intervals (second intervals) narrower than the first interval W1 within the narrow range including the provisional bias obtained at step S312 with the charging bias set in advance at step S2. (Step S313b). For example, in this embodiment, about 1/3 of the development bias variable band (Vb01 to Vb10) is set as a narrow range, and the provisional bias is between the development biases Vb05 and Vb06 as shown in FIG. In this case, the four points Vb04, Vb05, Vb06, and Vb07 are set as developing biases ((c) in the figure). Thus, in this embodiment, the second interval W2 is
W2 = Vb07-Vb06 = Vb06-Vb05 = Vb05-Vb04
It is said.
[0059]
With such a bias setting, four yellow solid images (FIG. 6) are sequentially formed on the photosensitive member 21 and further transferred onto the outer peripheral surface of the intermediate transfer belt 41 as shown in FIG. One patch image PI1 (Y) is formed (step S313c). Then, until it is determined in step S313d that patch images have been created for all patch creation colors, the patch creation color is set to the next color (step S313e), and steps S313b and S313c are repeated to repeat the steps (b) to (b) in FIG. As shown in d), the first patch images PI1 (C), PI1 (M), PI1 (K) are formed on the outer peripheral surface of the intermediate transfer belt 41 in the order of cyan (C), magenta (M), and black (K). Will continue to form.
[0060]
When 16 (= 4 types × 4 colors) first patch images PI1 (Y), PI1 (C), PI1 (M), and PI1 (K) are thus formed on the intermediate transfer belt 41, the patch at the head position is formed. The image density of the first patch image is measured by the patch sensor PS in order from the image (step S313f). Subsequently, in step S313g, a developing bias corresponding to the target density is obtained. Here, when the measurement result (image density) matches the target density, the development bias corresponding to the image density may be a provisional bias, and when they do not match, the result is shown in FIG. As shown, the optimum developing bias can be obtained by linear interpolation based on data D (Vb05) and D (Vb06) sandwiching the target density.
[0061]
When the optimum development bias has been obtained for all the patch creation colors, the process proceeds to step S302 in FIG. 12, and the optimum development bias obtained as described above is stored in the RAM 127, and the charging bias is calculated later. In a normal image forming process, it is read from the RAM 127 and set as a developing bias.
[0062]
As described above, also in the first developing bias calculation process (first processing mode), a patch image is created on the intermediate transfer belt (image carrier) 41 for each toner color as in the first embodiment. Since (Step S312c), density detection of the patch image (Step S312d), and cleaning removal of the patch image from the intermediate transfer belt 41 (Step S312d) are performed in order, the same effects as the first embodiment are obtained. are doing. That is, even if fog occurs when a patch image of a certain toner color is created, the intermediate transfer belt 41 is cleaned before creating a patch image for the next toner color, and the influence of fog is completely eliminated. Therefore, a patch image is always created on the intermediate transfer belt 41 that is free from contamination for each toner color, and the optimum developing bias can be determined with high accuracy.
[0063]
In the second embodiment, after obtaining the provisional value of the development bias, a plurality of patches are obtained while gradually changing the development bias (density control factor) within a narrow range including the provisional value for all toner colors. After the images PI1 (Y), PI1 (C), PI1 (M), and PI1 (K) are formed on the intermediate transfer belt (image carrier) 41, each patch image PI1 (Y), PI1 (C), PI1 The concentrations of (M) and PI1 (K) are collectively detected by the patch sensor PS. As described above, by performing the “second patch density detection process” of the present invention, the optimum developing bias can be finally obtained under the same conditions as the actual image forming procedure, which is higher than in the first embodiment. The optimum developing bias can be obtained with high accuracy.
[0064]
In the first development bias calculation process (first process mode), a development bias necessary for obtaining an image having a target density in a wide range and at a first interval W1 is provisionally obtained, and further includes a provisional bias. The developing bias necessary for obtaining the target density is determined by setting the developing bias in a narrow range and at a finer interval (second interval) W2, and this is finally set as the optimum developing bias. Therefore, the following effects can be obtained.
[0065]
For example, when the main power supply of the main body of the image forming apparatus is turned on, the state of the engine unit E cannot be predicted at all as described above. It is necessary to decide. Therefore, it is possible to divide the development bias variable band (Vb01 to Vb10) into a plurality of narrow ranges and execute the same processing as the bias calculation processing (1) in each narrow range to obtain the optimum development bias. However, this comparative example has a problem that the number of steps increases in proportion to the number of divisions, and it takes time to calculate the optimum developing bias. Conversely, if the number of divisions is reduced, the above problem can be solved, but the bias interval within one division range becomes wider than the second bias interval W2, and as a result, the calculation accuracy of the optimum developing bias is reduced. Another problem is that the image density cannot be accurately adjusted to the target density.
[0066]
On the other hand, in the present embodiment, the development bias is tentatively obtained by the bias calculation process (step S312) in a wide range as described above, and further in a narrow range near the provisional bias and fine. Since the optimum developing bias is calculated by changing the developing bias at the interval (second interval) W2, the optimum developing bias can be obtained in a shorter time and with higher accuracy than in the comparative example.
[0067]
Further, the development γ characteristic indicating the toner amount with respect to the development bias, that is, the change in image density, changes greatly according to the environmental condition, the durability condition, and the like, and is non-linear. The processing mode) has the excellent effects described below.
[0068]
FIG. 17 is a graph showing a typical example of development γ characteristics. As shown in the figure, even if the image forming apparatus has a development γ characteristic A under a certain environmental condition or the like, if the environmental condition or the like changes, the development γ characteristic of the image forming apparatus changes according to the change. The initial development γ characteristic A changes to the development γ characteristic B. In particular, the slope of the development γ characteristic is easily affected by the environmental conditions, and the slope changes greatly.
[0069]
Therefore, in the case of the development γ characteristic A, if the optimum development bias of the image forming apparatus is the value Vb (A) but changes to the development γ characteristic B due to a slight change in environmental conditions, the optimum development bias. The value greatly changes to the value Vb (B). Therefore, if such development γ characteristics are taken into consideration, it is inevitably necessary to widen the development bias variable band, and as described above, the first processing mode according to the present invention is applied to the calculation of the optimum development bias. Is more suitable.
[0070]
Further, the effect becomes more remarkable in an image forming apparatus using non-magnetic one-component toner among various toners. Hereinafter, the reason will be described in detail. In consideration of controllability of the toner concentration with respect to the carrier, non-magnetic one-component toner has been adopted in recent years. The image forming apparatus using the one-component toner has a feature that the charge amount of the toner is easily changed depending on the environment and the durability condition as compared with the image forming apparatus using the two-component toner. This is because the charge amount is relatively stable because the two-component toner has a large contact area with the carrier mixed with the toner, whereas the carrier for controlling the charge amount does not exist for the one-component toner. This is because the toner is charged only by the charging mechanism inside the developing device, and the contact area between the charging mechanism and the toner is much smaller than the contact area between the two-component toner and the carrier. Therefore, it can be said that it is even more preferable to apply the present invention to an image forming apparatus using non-magnetic one-component toner.
[0071]
Further, in order to improve the transferability of the toner, the amount of the external additive added to the toner may be larger than a general amount, for example, 1.5% or more. Also in this case, the usefulness of the present invention becomes remarkable. If this is the case, this external additive is also easily affected by the environment. If the amount of this external additive is 1.5% or more, the effect appears clearly, and the development γ characteristics change greatly due to changes in environmental conditions. Thus, it can be said that it is even more preferable to apply the present invention to an image forming apparatus using such toner.
[0072]
Note that, in an image forming apparatus that employs an intermediate transfer method, such as the image forming apparatus according to the present embodiment, an improvement in transferability is further demanded. There is a tendency to increase as compared with the forming apparatus, and it can be said that the usefulness of the present invention is also exhibited in this respect.
[0073]
In summary, when the present invention is applied to an image forming apparatus and an image forming method using a toner that is a non-magnetic one component and contains 1.5% or more of an external additive, an excellent effect, that is, a toner image is obtained. The effect that the optimum value of the density control factor necessary for adjusting the image density to the target density can be determined more accurately and efficiently becomes more remarkable.
[0074]
B-2-1-2. Second developing bias calculation process (second processing mode)
By the way, in this embodiment, when the second processing mode is selected in step S301 in FIG. 12, the second developing bias calculation process is executed to determine the optimum developing bias. This is because in the case of 2), (3) and (5), the state change of the engine part E is estimated to be small. That is, the optimum charging bias and the optimum developing bias change according to fatigue and change with time of the photoreceptor and toner, but the changes have a certain degree of continuity. Therefore, in the case of the above criteria (2), (3) and (5), the optimum developing bias can be predicted based on the immediately preceding image density measurement result (step S313f or step S322g described later). Therefore, in the development bias calculation process (step S3) according to this embodiment, if it is determined that the above-described determination criteria (2), (3) and (5) are satisfied, the process is simplified as follows. In addition, the optimum developing bias is accurately calculated.
[0075]
In the second developing bias calculation process, setting is made to form patch images for all colors (four colors of yellow (Y), cyan (C), magenta (M), and black (K) in this embodiment). (Step S321), the process proceeds to Step S322 to execute the bias calculation process (2) in a narrow range to obtain the optimum developing bias without obtaining the provisional bias. The processing contents will be described below with reference to FIG.
[0076]
FIG. 18 is a flowchart showing the contents of the bias calculation process (2) in the narrow range of FIG. FIG. 19 is a schematic diagram showing the processing content of FIG. This calculation process is greatly different from the bias calculation process (1) in the narrow range described above. In the calculation process (1) of FIG. 15, the charging bias is set to a predetermined value and a narrow range including a provisional bias is included. While four types of development bias are set in the range (step S313b), in this bias calculation process (2), the optimum charging bias obtained by the previous image density measurement and stored in the RAM 127 is charged. In addition to being set as the bias, four types of development bias in a narrow range including the optimum development bias stored in the RAM 127 are set (step S322b), and other configurations are the same. Therefore, the description of the same configuration is omitted here.
[0077]
As described above, in the second processing mode, four types of development biases are set in a narrow range using the immediately preceding image density measurement result (previous optimum development bias) and at the second interval without obtaining a provisional bias. Since the optimum development bias is obtained by forming each color patch image, the optimum development bias can be obtained in a shorter time as compared with the first processing mode (step S312 + step S313).
[0078]
The second embodiment is common to the invention described in, for example, Japanese Patent Application Laid-Open No. 10-239924 in terms of optimizing the developing bias and the charging bias. However, the optimum developing bias is more accurate than this conventional technique. It has a unique effect that it can be obtained. The reason will be described. In this prior art, three sets of development bias and charging bias are stored in advance, and a patch image is formed by each of these three development biases. Therefore, in order to cover a range in which the developing bias can change, that is, a range almost equal to the developing bias variable band, the three developing biases must be set at relatively wide intervals.
[0079]
On the other hand, in the present embodiment, the development bias is changed within a narrow range including the immediately preceding optimum development bias in the development bias variable band (Vb01 to Vb10). The developing bias interval (second interval) is narrower than that of the prior art. As a result, the optimum developing bias can be calculated with higher accuracy. Note that simply narrowing the range for changing the development bias makes it difficult to calculate the optimum development bias accurately because the optimum development bias to be obtained is out of the range, but in this embodiment, the optimum Since a narrow range is set around the development bias, the probability of such a problem occurring is extremely small.
[0080]
The optimum development bias thus obtained is updated to the latest one by rewriting the optimum development bias already stored in the RAM 127 (step S302 in FIG. 12). Returning to FIG. 3, the optimum development bias calculated as described above is read from the RAM 127 and set as the development bias. Subsequently, an optimum charging bias is calculated (step S5) and set as a charging bias (step S6).
[0081]
Furthermore, according to the second embodiment, the first and second processing modes are prepared in advance to determine the optimum developing bias, and the first processing mode or the second processing mode is set according to the operation state of the apparatus. Since it is selectively executed, the most appropriate processing mode can be selected and executed according to the operation status, and the optimum value of the developing bias, which is one of the density control factors, is determined efficiently and with high accuracy. can do.
[0082]
B-2-2. Optimal charging bias calculation process
FIG. 20 is a flowchart showing the contents of the charging bias calculation process according to the second embodiment. In this charging bias calculation process (step S5), as in the case of the development bias calculation process, first, one of the third and fourth processing modes is selected as the processing mode in accordance with the operation status of the apparatus (step S5). S501). In the third processing mode, as will be described later, a plurality of patch images are formed while changing the charging bias within a narrow range (about 1/3 of the variable region) including a preset default value, and the density of each patch image is determined. Is used to determine the charging bias necessary for obtaining the optimum image density, and is suitable when the state of the engine unit E cannot be predicted. On the other hand, in the fourth processing mode, as will be described later, the optimum charging bias is determined while changing the charging bias within a narrow range (about 1/3 of the variable region) including the previous optimum charging bias. This is suitable when the state change of the part E is small. In this embodiment, the specific selection determination in step S501 is executed based on the following criteria.
[0083]
(1) When power is turned on → Third processing mode
When the power is turned on, the state of the engine part E cannot be predicted at all. Therefore, the optimum charging bias is determined while changing the charging bias within a narrow range (about 1/3 of the variable region) including a preset default value. To do.
[0084]
(2) When returning from sleep and the sleep time is less than the predetermined time → Fourth processing mode
In the case of return from sleep, the state of the engine unit E may have changed greatly. However, if the sleep time is short, it is estimated that the state change of the engine unit E is small. The optimum charging bias is determined while changing the charging bias within a narrow range including the bias (about 1/3 of the variable region).
[0085]
(3) When returning from sleep and the fixing temperature of the fixing unit 5 is equal to or higher than a predetermined temperature → the fourth processing mode
In the case of returning from sleep, the state of the engine unit E may have changed greatly. However, if the fixing device that is a heat source in the fixing unit 5 is kept at a high temperature, the state of the engine unit E Since the change is estimated to be small, the optimum charging bias is determined while changing the charging bias within a narrow range (about 1/3 of the variable region) including the previous optimum charging bias.
[0086]
(4) When returning from sleep (except cases (2) and (3) above) → Third processing mode
Other than the above (2) and (3), the state of the engine unit E may have changed greatly when returning from sleep. Therefore, a narrow range including a preset default value (approximately 1 of the variable region). In (3), the optimum charging bias is determined while changing the charging bias.
[0087]
(5) During continuous image formation → Fourth processing mode
When image formation is continuously performed, it is unlikely that the state of the engine unit E will change significantly from the previous density adjustment, so a narrow range including the previous optimum charging bias (about 1/3 of the variable region). The optimum charging bias is determined while changing the charging bias in ().
[0088]
When the third processing mode is selected based on the above criteria, the first charging bias calculation process (steps S511, S512, and S502) is executed to determine the optimum charging bias, while the fourth processing mode is selected. Is selected, the second charging bias calculation process (steps S521, S522, S502) is executed to determine the optimum charging bias. In the following, description will be given separately.
[0089]
B-2-2-1. First charging bias calculation processing (third processing mode)
In the first charging bias calculation process, as shown in FIG. 20, patch images for all colors (in this embodiment, four colors of yellow (Y), cyan (C), magenta (M), and black (K)) are used. (Step S511), the process proceeds to step S512, and the charging bias is set in four stages at relatively narrow intervals within a narrow range that includes a preset default value. A plurality of patch images are formed while changing, and a charging bias necessary to obtain an optimum image density is obtained based on the density of each patch image.
[0090]
FIG. 21 is a flowchart showing the processing content in step S512, that is, the content of the bias calculation processing (3) in the narrow range of FIG. In this calculation process, the color for creating the patch image is set to the first color, for example, yellow (step S512a). Then, the charging bias is set in four stages at a relatively narrow interval (third interval) within the narrow range including the predetermined value set in advance in step S2 (step S512b). Thus, unlike the development bias calculation process, the charging bias calculation process executes only the calculation process in the narrow range without performing the calculation process in the wide range. In this embodiment, about 1/3 of the variable band (Va01 to Va10) of the charging bias is set as a narrow range. For example, the default value or the immediately preceding optimum charging bias is as shown in FIG. When the charging bias is between Va05 and Vb06, the four points Va04, Va05, Va06, and Va07 are set as the charging bias. Thus, in this embodiment, the third interval W3 is
W3 = Va07-Va06 = Va06-Va05 = Va05-Va04
It is said.
[0091]
When four types of charging bias are set for the yellow color as described above, each yellow halftone image (FIG. 10) is formed on the photoconductor 21 while the charging bias is gradually increased from the lowest value Va04. These are sequentially formed and transferred to the outer peripheral surface of the intermediate transfer belt 41 to form the second patch image PI2 (Y) (FIG. 11 (a): Step S512c).
[0092]
In the next step S512d, it is determined whether or not the second patch image has been generated for all the patch generation colors, and while it is determined “NO”, the patch generation color is set to the next color (step S512e). Steps S512b to S512d are repeated, and the second patch is formed on the outer peripheral surface of the intermediate transfer belt 41 in the order of cyan (C), magenta (M), and black (K) as shown in FIGS. 11 (b) to 11 (d). Images PI2 (C), PI2 (M), and PI2 (K) are further formed.
[0093]
On the other hand, if “YES” is determined in step S512d, the image density of 16 (= 4 types × 4 colors) patch images PI2 (Y), PI2 (C), PI2 (M), and PI2 (K) are determined as patch sensors. Measure with PS (step S512f). Subsequently, in step S512g, a charging bias corresponding to the target density is obtained. Here, if the measurement result (image density) matches the target density, the charging bias corresponding to the image density may be set as the optimum charging bias. As shown in FIG. 5, the optimum charging bias can be obtained by linear interpolation based on data D (Va05) and D (Va06) sandwiching the target density.
[0094]
When the optimum charging bias is obtained for all the patch creation colors, the process proceeds to step S502, where the optimum charging bias obtained as described above is stored in the RAM 127, read out from the RAM 127 and charged in a normal image forming process. Set as bias.
[0095]
B-2-2-2. Second charging bias calculation process (fourth processing mode)
In this embodiment, based on the same reason as in the development bias calculation process, when the fourth processing mode is selected in step S501 in FIG. 20, the second charging bias calculation process is executed to determine the optimum charging bias. .
[0096]
In the second charging bias calculation process, setting is made to form patch images for all colors (four colors of yellow (Y), cyan (C), magenta (M), and black (K) in this embodiment). (Step S521), the process proceeds to Step S522 to execute a bias calculation process (4) in a narrow range to obtain an optimum charging bias (Step S522).
[0097]
FIG. 22 is a flowchart showing the contents of the bias calculation process (4) in the narrow range of FIG. This calculation process is greatly different from the bias calculation process (3) in the narrow range described above, in the calculation process (3) of FIG. While the bias is set (step S512b), in this bias calculation process (4), four types of charging in a narrow range are performed based on the charging bias obtained by the previous image density measurement and stored in the RAM 127. The bias is set (step S515b), and other configurations are the same. Therefore, the description of the same configuration is omitted here.
[0098]
When the optimum developing bias is obtained for all the patch creation colors, the process proceeds to step S502, where the optimum charging bias obtained as described above is stored in the RAM 127, read out from the RAM 127 and charged in the normal image forming process. Set as bias.
[0099]
As described above, the third and fourth processing modes are prepared in advance to determine the optimum charging bias, and the third processing mode or the fourth processing mode is selectively executed according to the operation state of the apparatus. Therefore, the most appropriate processing mode can be selected and executed according to the operation state, and the optimum value of the charging bias, which is one of the density control factors, can be determined efficiently and with high accuracy.
[0100]
The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the first and second embodiments, the density adjustment of the toner image is performed by performing the development bias calculation process and the charging bias calculation process. However, when only one of the calculation processes is performed, A plurality of patch images are formed on the intermediate transfer belt 41 while changing the density control factor, for example, the exposure amount and the transfer bias, and the density of each patch image is detected by the patch sensor PS to adjust the density of the toner image. The present invention can also be applied to an image forming apparatus to be performed. In these image forming apparatuses as well, in the same manner as in the above-described embodiment, patch images are created on the intermediate transfer belt (image carrier) 41 for each toner color, patch image density detection, and patches from the intermediate transfer belt 41 are used. By performing the cleaning removal of the image in this order, it is possible to determine the optimum value of the density control factor such as the developing bias, the charging bias, the transfer bias, and the exposure amount with high accuracy while suppressing the influence of the fog.
[0101]
In the above embodiment, the second processing mode is selectively executed based on the expectation that the state change of the engine part E is small in the case of the determination criteria (2), (3) and (5). However, there may be a case where the state change becomes larger than expected and the optimum developing bias cannot be determined in the second processing mode. In order to appropriately cope with such a case, as shown in FIG. 23, it is determined that the optimum developing bias could not be calculated for all patch creation colors in the second processing mode (step S323). Then, the process may proceed to step S312 to further execute the first processing mode. By doing so, it is possible to determine the optimum developing bias with high accuracy in a flexible manner even when the state of the engine section E changes greatly.
[0102]
In the above embodiment, about 1/3 of the development bias variable band (Va01 to Va10) is set as the narrow range. However, the width of the narrow range is not limited to this, but this width is As the width becomes wider, the meaning of using the narrow range is lessened, and the calculation accuracy of the optimum development bias is lowered. Moreover, although the narrow ranges in the first and second processing modes have the same width, it is not essential that they are the same, and they may be set to be different from each other. The same applies to the case where the charging bias is in a narrow range.
[0103]
The image forming apparatus according to the above embodiment is a printer that forms an image given from an external device such as a host computer via an interface 112 on a sheet such as copy paper, transfer paper, paper, and an OHP transparent sheet. However, the present invention can be applied to all electrophotographic image forming apparatuses such as copying machines and facsimile machines.
[0104]
Furthermore, in the above embodiment, the toner image on the photosensitive member 21 is transferred to the intermediate transfer belt 41 functioning as an image carrier, and this toner image is used as a patch image to detect the image density and based on the detection result. The optimum development bias and optimum charging bias are calculated, but transfer media other than the intermediate transfer belt (transfer drum, transfer belt, transfer sheet, intermediate transfer drum, intermediate transfer sheet, reflective recording sheet, transmissive memory sheet, etc.) The present invention can also be applied to an image forming apparatus that forms a patch image by transferring a toner image to the toner image. Also, instead of forming a patch image on the transfer medium, a patch sensor that detects the density of the patch image on the photoconductor is provided, and this patch sensor detects the image density of each patch image on the photoconductor, and the detection result The optimum developing bias and optimum charging bias may be calculated based on the above. In this case, the photoreceptor corresponds to the “image carrier” of the present invention.
[0105]
【The invention's effect】
As described above, according to the present invention, for each toner color, creation of a patch image on the image carrier, detection of the density of the patch image, and cleaning removal of the patch image from the image carrier are performed in this order. Therefore, it is possible to create a patch image on an image carrier that is always free of contamination for each toner color. Therefore, even if fog occurs when creating a patch image of a certain toner color, the image carrier is cleaned before creating the patch image for the next toner color, and the influence of fog can be completely eliminated. For each toner color, the optimum value of the density control factor necessary for adjusting the image density of the toner image to the target density can be determined with high accuracy.
[0106]
In addition, the value obtained as described above is used as a provisional value, and the second patch density detection process is executed, and the image density of each color toner image is determined based on the image density detected by the second patch density detection process. If the optimum value of the density control factor required to adjust to the target density is finally obtained, the final optimum value is obtained under conditions that match the actual color image formation procedure. The optimum value can be determined with higher accuracy.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention.
2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG.
FIG. 3 is a flowchart showing a density adjustment operation in the image forming apparatus of FIG. 1;
FIG. 4 is a flowchart showing the contents of development bias calculation processing according to the first embodiment.
FIG. 5 is a schematic diagram showing the processing content of FIG. 4;
FIG. 6 is a diagram illustrating a first patch image.
FIG. 7 is a diagram showing a first patch image formation order in the first embodiment.
FIG. 8 is a flowchart showing the content of a charging bias calculation process according to the first embodiment.
FIG. 9 is a schematic diagram showing the processing content of FIG. 8;
FIG. 10 is a diagram illustrating a second patch image.
FIG. 11 is a diagram showing a second patch image formation order in the first embodiment.
FIG. 12 is a flowchart showing the contents of development bias calculation processing according to the second embodiment.
13 is a flowchart showing the contents of bias calculation processing in a wide range in FIG.
14 is a schematic diagram showing the processing content of FIG. 13 and the content of bias calculation processing in a narrow range, which will be described later.
15 is a flowchart showing the contents of bias calculation processing (1) in the narrow range of FIG.
FIG. 16 is a diagram illustrating a first patch image formation order in the second embodiment.
17 is a graph showing changes in development γ characteristics accompanying changes in environmental conditions and the like in the image forming apparatus of FIG.
FIG. 18 is a flowchart showing the contents of bias calculation processing (2) in the narrow range of FIG.
FIG. 19 is a schematic diagram showing the processing content of FIG. 18;
FIG. 20 is a flowchart showing the content of a charging bias calculation process according to the second embodiment.
FIG. 21 is a flowchart showing the contents of bias calculation processing (3) in the narrow range of FIG. 20;
22 is a flowchart showing the contents of bias calculation processing (4) in the narrow range of FIG.
FIG. 23 is a diagram showing another embodiment of the image forming method according to the present invention.
[Explanation of symbols]
1 ... Control unit (control means)
4. Transfer unit (transfer means)
12 ... Engine controller (control means)
21 ... Photoconductor
22: Charging roller (charging means)
23. Developing section (developing means)
23Y, 23C, 23M, 23K ... developing device (developing means)
41. Intermediate transfer belt (transfer medium, image carrier)
121: Charging bias generator
123 ... CPU (control means)
125: Development bias generator
127 ... RAM (storage means)
PS ... Patch sensor (Density detection means)

Claims (7)

In an image forming apparatus that forms toner images of different colors from each other and forms a color image by superimposing the toner images of the colors.
An image carrier for carrying a patch image;
Density detecting means for detecting the image density of a patch image formed on the image carrier;
A control means that can change and set the concentration control factor within a predetermined variable band, and can set the range for changing the concentration control factor within the variable band in two steps, a wide range and a narrow range;
The control means includes
For each color, the following first patch density detection process is performed while changing the density control factor stepwise at a first interval within a wide range, and the image density detected by the first patch density detection process After obtaining the value of the density control factor necessary for adjusting the image density of the toner image of each color to the target density based on the
The following second patch density detection process is executed, and density control factors necessary for adjusting the image density of each color toner image to the target density based on the image density detected by the second patch density detection process An image forming apparatus characterized by determining an optimum value.
In the first patch density detection process, a plurality of toner images are formed on the image carrier as patch images while changing a density control factor that affects the image density of the toner image, and the density of each patch image is set. After the detection by the density detection means, the plurality of patch images are removed by cleaning from the image carrier.
In the second patch density detection process, a plurality of toner images are formed on the image carrier as patch images while stepwise changing density control factors within a narrow range including the provisional value for all toner colors. Thereafter, the density of each patch image is collectively detected by the density detecting means.   The image forming apparatus according to claim 1, wherein the control unit changes the density control factor in a stepwise manner at a second interval narrower than the first interval in the second patch density detection process. A photoconductor, a charging unit that charges the surface of the photoconductor, and a developing unit that exposes the electrostatic latent image formed on the surface of the photoconductor with toner to form a toner image,
The photoconductor functions as the image carrier,
The image forming apparatus according to claim 1, wherein the control unit determines an optimum value of at least one of a developing bias applied to the developing unit and a charging bias applied to the charging unit as a density control factor. Functions as a photosensitive member, a charging unit that charges the surface of the photosensitive member, a developing unit that exposes an electrostatic latent image formed on the surface of the photosensitive member with toner to form a toner image, and the image carrier And a transfer means for transferring the toner image on the photoconductor to the transfer medium.
The image forming apparatus according to claim 1, wherein the control unit determines an optimum value of at least one of a developing bias applied to the developing unit and a charging bias applied to the charging unit as a density control factor.   The image forming apparatus according to claim 1, wherein a toner image is formed using a non-magnetic one-component toner.   The image forming apparatus according to claim 1, wherein a toner image is formed using a toner containing 1.5% or more of an external additive. In an image forming method of forming toner images of different colors from each other and forming a color image by superimposing the toner images of the colors.
The density control factor that affects the image density of the toner image can be changed within a predetermined variable band, and the range in which the density control factor is changed within the variable band can be set in two stages, a wide range and a narrow range. And
A first step of executing the following first patch density detection process for each color;
A second step of tentatively obtaining a value of a density control factor necessary for adjusting the image density of each color toner image to a target density based on the image density detected in the first step;
A third step of executing the following second patch density detection process;
And a fourth step of determining an optimum value of a density control factor necessary for adjusting the image density of each color toner image to a target density based on the image density detected in the third step. Image forming method.
The first patch density detection process forms a plurality of toner images on the image carrier as patch images while gradually changing density control factors at a first interval within a wide range. After the density is detected by the density detection means, the plurality of patch images are removed from the image carrier by cleaning.
In the second patch density detection process, a plurality of toner images are formed on the image carrier as patch images while stepwise changing density control factors within a narrow range including the provisional value for all toner colors. Thereafter, the density of each patch image is collectively detected by the density detecting means.

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