JP2003223023A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device and an image forming method by which the optimum value of density control factor exerting influence on the image density of a toner image is obtained in a mode corresponding to consecutive image forming so as to be able to efficiently decide the optimum value. <P>SOLUTION: Two processing modes having the different number of steps from each other are previously prepared. In a 1st processing mode, the provisional value of optimum developing bias is obtained by changing developing bias in a wide range (entire variable area of developing bias), and further the optimum developing bias is decided while changing the developing bias in a narrow range (about 1/3 of the variable area) based on the provisional value. In a 2nd processing mode, the optimum developing bias is decided while changing the developing bias in the narrow range (about 1/3 of the variable area) including the previous optimum developing bias. Then, at the consecutive image forming time, the optimum developing bias is decided by selectively performing the 2nd processing mode having the smaller number of steps. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and an image forming method for optimizing a density control factor affecting image density.

[0002]

2. Description of the Related Art In this type of image forming apparatus, the image density may change due to fatigue of the photoconductor and toner, a change over time, and a change in temperature and humidity around the apparatus. Therefore, conventionally, a density control factor that affects the image density of the toner image, such as a charging bias, a developing bias,
Many techniques have been proposed for stabilizing the image density by appropriately adjusting the exposure amount and the like. For example, there is one in which the image density is stabilized by appropriately adjusting the charging bias and the developing bias (see Patent Document 1). That is,
In the conventional technique described in Patent Document 1, the reference patch image is formed on the photoconductor while changing the charging bias and / or the developing bias, and the image density of each reference patch is detected. Then, the optimum charging bias and developing bias are determined based on these detected values, and the density of the toner image is adjusted. In this specification, for convenience of description, a plurality of patch images are formed, the densities of the patch images are detected, and the image density of the toner image is adjusted to the target density based on the image densities. A series of processing contents of determining the optimum value of the required concentration control factor is called a "processing mode".

Further, this processing mode is executed at the following timing. That is, after the main power supply of the image forming apparatus main body is turned on, it is considered that the image forming state is reached, for example, the fixing temperature has reached a specified temperature or just after that. When the timer is set in, the density adjustment is periodically performed, for example, every two hours.

[0004]

[Patent Document 1] Japanese Patent Application Laid-Open No. 10-239924 (

~

(FIG. 9)

[0005]

By the way, in the above-mentioned conventional apparatus, in order to increase the accuracy of the optimum value, for example, the interval for changing the charging bias and / or the developing bias is narrowed to increase the number of reference patches to be created. Can be considered. However, as the number of reference patches created increases, the number of steps increases, which takes time to calculate the optimum value, resulting in inefficiency.

Further, in an actual image forming apparatus, the state of the engine section (image forming means) greatly differs depending on the operating condition of the apparatus. For example, while the image forming process is continuously executed, the state of the engine unit is relatively small, but the state of the engine unit is highly likely to be greatly changed when the power is turned on.

Therefore, if the density can be adjusted in the processing mode according to the state, the density can be adjusted efficiently and with high accuracy. For example, the optimum charging bias and the optimum developing bias change depending on the fatigue of the photoconductor and the toner, the change over time, and the like, but the changes have some continuity. Therefore, when the density adjustment is repeatedly performed, the density adjustment can be performed more accurately if the density adjustment is performed based on the density control factor obtained by the immediately preceding 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.

However, in the prior art, since the processing mode is single and fixed, there is room for improvement in terms of efficiency and accuracy. In particular, when image formation is performed intermittently, the state of the engine unit is unlikely to change significantly, and it is expected that the amount of deviation from the density control factor obtained by the immediately preceding density adjustment will be small. Therefore, it is preferable to find the optimum value of the density control factor corresponding to this, but in the prior art, it is not considered at all whether the timing for finding the optimum value is during continuous image formation or other times. The optimum value was uniformly sought.

The present invention has been made in view of the above problems, and finds an optimum value of a density control factor that affects the image density of a toner image in a mode corresponding to continuous image formation, and efficiently determines the optimum value. An object of the present invention is to provide an image forming apparatus and an image forming method capable of performing the above.

[0010]

One aspect of the present invention is as follows.
An image forming apparatus and an image forming method for optimizing a density control factor that affects an image density at a predetermined timing, and is configured as follows to achieve the above object. This image forming apparatus has a first processing mode for optimizing a density control factor in a plurality of steps and a second processing mode for optimizing a density control factor in a number of steps smaller than the number of steps in the first processing mode. The processing mode can be selectively executed, and the second processing mode is selectively executed when the predetermined timing is the time of continuous image formation. Further, in this image forming method, as the processing mode for optimizing the density control factor that affects the image density, there are a first processing mode for optimizing the density control factor in a plurality of steps and a first processing mode. And a second processing mode for optimizing the density control factor with a number of steps smaller than the number of steps of
It is characterized in that the second processing mode is executed.

In the invention thus constituted, the density control is performed with the first processing mode and the number of steps smaller than the first processing mode as the processing mode for optimizing the density control factor affecting the image density. And a second processing mode for optimizing the factors. When the timing for optimizing the density control factor is continuous image formation, it is expected that the state of the apparatus is unlikely to change significantly. Therefore, the number of steps in the two processing modes is small. The second processing mode is selectively executed. In the second processing mode, the density control factor is optimized in a smaller number of steps than in the first processing mode, and the processing is simpler than when the first processing mode is selected. Therefore, it becomes possible to efficiently determine the optimum value of the concentration control factor.

Another aspect of the present invention is an image forming apparatus and an image forming method for setting a density control factor affecting image density to an optimum value at a predetermined timing. It is configured like. This image forming apparatus sets the density control factor based on the optimum value set immediately before when the predetermined timing is the time of continuous image formation, and when the predetermined timing is not the time of continuous image formation. Is characterized in that the concentration control factor is set independently of the immediately preceding optimum value. In addition, this image forming method includes a step of determining whether or not the predetermined timing is during continuous image formation, and in the case of continuous image formation, the density control based on the optimum value set immediately before. While setting the factor, when the predetermined timing is not during continuous image formation, a step of setting the density control factor regardless of the immediately preceding optimum value is provided.

In the invention thus constructed, the density control factor is not uniformly set at a predetermined timing as in the prior art, but first, it is determined whether or not the predetermined timing is for continuous image formation. After determining, the concentration control factor is set in a manner according to the determination result, so that the concentration control factor can be set efficiently. That is, since it is unlikely that the state of the apparatus will change significantly during continuous image formation, it is possible to optimize the density control factor by setting the density control factor based on the optimum value that was set immediately before. It is possible to efficiently determine the value.

[0014]

BEST MODE FOR CARRYING OUT 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. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This image forming apparatus includes yellow (Y), cyan (C), magenta (M),
This is an apparatus for forming a full-color image by superposing four color toners of black (K) or forming a monochrome image using only the toner of black (K). 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 section E in response to a command from the main controller 11. Then, an image corresponding to the image signal is formed on the sheet S.

As described above, in the engine section E which functions as an image forming means, a toner image can be formed on the photoconductor 21 of the image carrier unit 2. That is, the image carrier unit 2 includes a photoconductor 21 rotatable in the direction of the arrow in FIG. 1, and further, around the photoconductor 21 along the rotation direction thereof, a charging roller 22 as a charging unit and a developing unit. Developing units 23Y, 23C, 23M and 23K, and a cleaning unit 24 are arranged. A high voltage is applied to the charging roller 22 from the charging bias generator 121, and the charging roller 22 contacts the outer peripheral surface of the photoconductor 21 to uniformly charge the outer peripheral surface.

Then, the laser beam L is emitted from the exposure unit 3 toward the outer peripheral surface of the photoconductor 21 charged by the charging roller 22. This exposure unit 3 is shown in FIG.
As shown in FIG. 2, the photoconductor 21 is electrically connected to the image signal switching unit 122, and the laser beam L is scanned and exposed on the photoconductor 21 in accordance with the image signal given through the image signal switching unit 122. An electrostatic latent image corresponding to the image signal is formed on 21. For example, the CPU 1 of the engine controller 12
When the image signal switching unit 122 is in conduction with the patch creating module 124 based on a command from the H.23, the patch image signal output from the patch creating module 124 is given to the exposure unit 3 to form a latent patch image. To be done.
On the other hand, the image signal switching unit 122 is the main controller 11
When it is electrically connected to the CPU 111, the laser light L emits the laser light L in accordance with the image signal given from the external device such as the host computer through the interface 112.
An electrostatic latent image corresponding to an image signal is formed on the photoconductor 21 by scanning and exposing the same.

The electrostatic latent image thus formed is developed by the developing unit 23.
The toner is developed by. That is, in this embodiment, as the developing unit 23, a developing unit 23Y for yellow, a developing unit 23C for cyan, a developing unit 23M for magenta, and a developing unit 23K for black are arranged in this order along the photoreceptor 21. Has been done. These developing devices 23Y, 23
C, 23M, and 23K are respectively configured to come into contact with and separate from the photoconductor 21, and in accordance with a command from the engine controller 12, the four developing units 23Y, 23M, and
One of the developing units 23C and 23K selectively selects the photoconductor 2
1 and a high voltage is applied by the developing bias generator 125 to apply toner of a selected color to the surface of the photoconductor 21 to visualize the electrostatic latent image on the photoconductor 21.

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 unit 23K and the cleaning unit 24. The transfer unit 4
The structure of will be described in detail later.

Further, from the primary transfer region R1 in the circumferential direction (see FIG.
The cleaning unit 24 is arranged at a position advanced in the direction of the arrow) to scrape off the toner remaining on the outer peripheral surface of the photoconductor 21 after the primary transfer.

Next, the structure of the transfer unit 4 will be described. In this embodiment, the transfer unit 4 includes rollers 4
2 to 47, an intermediate transfer belt 41 wound around each of the rollers 42 to 47, and a secondary transfer roller 48 that secondarily transfers the intermediate toner image transferred to the intermediate transfer belt 41 onto the sheet S. ing. A primary transfer voltage is applied to the intermediate transfer belt 41 from the transfer bias generator 126. When a color image is transferred to the sheet S, the toner images of the respective colors formed on the photoconductor 21 are superposed on the intermediate transfer belt 41 to form a color image, and the paper feeding / discharging unit 6 is fed. The sheet S is taken out from the cassette 61, the manual feed tray 62 or an additional cassette (not shown) by the paper section 63, and the secondary transfer area R2
Transport to. Then, a color image is secondarily transferred onto this sheet S to obtain a full-color image. Further, when a monochrome image is transferred to the sheet S, only the black toner image is formed on the photoconductor 21 on the intermediate transfer belt 41, and the black toner image is conveyed to the secondary transfer region R2 in the same manner as in the case of the color image. And transferred to the sheet S to obtain a monochrome image.

After the secondary transfer, the toner remaining on the outer peripheral surface of the intermediate transfer belt 41 is removed by the belt cleaner 49. This belt cleaner 4
9 is arranged to face the roller 46 with the intermediate transfer belt 41 interposed therebetween, and a cleaner blade comes into contact with the intermediate transfer belt 41 at an appropriate timing to scrape off the toner remaining on the outer peripheral surface of the cleaner blade. Drop it.

A patch sensor PS for detecting the density of the patch image formed on the outer peripheral surface of the intermediate transfer belt 41 is arranged near the roller 43 as described later, and the intermediate transfer belt 41 is also provided. A reading sensor for synchronization RS for detecting the reference position of is arranged.

Returning to FIG. 1, the description of the structure of the engine section E will be continued. The sheet S to which the toner image has been transferred by the transfer unit 4 is arranged downstream of the secondary transfer region R2 along a predetermined paper feed path (two-dot chain line) by the paper feed section 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.

The paper discharge section 64 has two paper discharge paths 641.
a, 641b, and one discharge path 641a extends from the fixing unit 5 to the standard discharge tray, and
The other sheet discharging path 641b extends between the sheet re-feeding unit 66 and the multi-bin unit substantially parallel to the sheet discharging path 641a. 3 along these paper discharge paths 641a and 641b
A pair of roller pairs 642 to 644 is provided, and the sheet S having been fixed is discharged toward the standard discharge tray or the multi-bin unit side, and a re-feed unit for forming an image on the other side as well. It is transported to the 66 side.

As shown in FIG. 1, the re-feeding section 66 is
The sheet S reversely conveyed from the paper discharge unit 64 as described above is fed along the re-feed path 664 (two-dot chain line) to the paper feed unit 63.
Of the three re-feeding roller pairs 6 arranged along the re-feeding path 664.
61 to 663. In this way, the paper output unit 6
The sheet S conveyed from the sheet No. 4 is returned to the gate roller pair 637 along the sheet re-feeding path 664, so that the sheet feeding unit 6
3, the non-image forming surface of the sheet S is the intermediate transfer belt 4
The image can be secondarily transferred to the surface of the sheet by facing the direction 1.

In FIG. 2, reference numeral 113 indicates an interface 11 from an external device such as a host computer.
2 is an image memory provided in the main controller 11 for storing an image given via
Reference numeral 7 is a control data or CPU for controlling the engine section E.
Reference numeral 128 is a RAM for temporarily storing the calculation result and the like in 123, and reference numeral 128 is a ROM for storing the calculation program executed by the CPU 123.

B. Image Density Adjusting Operation in Image Forming Apparatus Next, an image density adjusting operation in the image forming apparatus configured as described above will be described.

FIG. 3 is a flow chart showing the density adjusting 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 perform the density adjustment operation to update and set the developing bias and the charging bias. For example, the bias setting may be started when an image can be formed after the main power of the image forming apparatus main body is turned on. Further, a continuous use time may be measured by a timer (not shown) provided in the apparatus body, and bias setting may be started every several hours.

When "YES" is determined in this step S1 and 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). Further, subsequently, step S5 is executed to calculate the optimum charging bias and set it as the charging bias (step S
6). In this way, the development bias and the charging bias are optimized. Hereinafter, the developing bias calculation process (step S3) and the charging bias calculation process (step S5)
The contents of each will be described in detail.

B-1. Developing Bias Calculation Processing FIG. 4 is a flowchart showing the contents of the developing bias calculation processing of FIG. In the developing bias calculation process (step S3), first, one of the first and second process modes is selected as the process mode according to the operation status of the apparatus (step S301). In the first processing mode, as will be described later, the developing bias is changed within a wide range (the entire developing bias variable region) to obtain a provisional value of the optimum developing bias, and based on the provisional value, a narrow range (about 1 The optimum developing bias is determined while changing the developing bias within / 3), and is suitable when the state of the engine section E cannot be predicted. On the other hand, the second processing mode determines the optimum developing bias while changing the developing bias within a narrow range (about 1/3 of the variable region) including the previous optimum developing bias as will be described later. It is suitable when the state of the part E changes little. Note that in this embodiment, step S30
The specific selection judgment in 1 is executed based on the following criteria.

(1) When the power is turned on → the first processing mode When the power is turned on, since the state of the engine section E cannot be predicted at all, the optimum developing bias is changed while changing the developing bias in the entire variable region of the developing bias. decide.

(2) When returning from sleep and the sleep time is less than the predetermined time → In the case of returning from the second processing mode sleep, the state of the engine section E may have changed significantly, When the time is short, the state change of the engine section E is presumed to be small. Therefore, while changing the developing bias within the narrow range (about 1/3 of the variable region) including the optimum developing bias of the previous time, the optimum developing bias is changed. To decide.

(3) Fixing unit 5 when returning from sleep
If the fixing temperature is higher than a predetermined temperature, the state of the engine section E may have changed significantly when returning to the second processing mode sleep state. However, if the fixing device that is the heat source in the fixing unit 5 is When the temperature is maintained at a high temperature, the state change of the engine section E is presumed to be small. Therefore, the narrow range including the optimum developing bias at the previous time (about 1 / the variable range) is included.
The optimum developing bias is determined while changing the developing bias in 3).

(4) At the time of returning from sleep (excluding the cases (2) and (3) above) → first processing mode Except for (2) and (3) described above, the state of the engine section E is at the time of returning from sleep. Since there is a possibility that it has changed significantly, the optimum developing bias is determined while changing the developing bias in the entire variable region of the developing bias.

(5) At the time of continuous image formation → second processing mode When image formation is continuously performed, the state of the engine section E is unlikely to change significantly from the last time the density adjustment was performed. The optimum developing bias is determined while changing the developing bias within a narrow range (about 1/3 of the variable region) including the optimum developing bias of.

When the first processing mode is selected on the basis of the above criteria, the first developing bias calculation processing (steps S311 to S313, S302) is executed to determine the optimum developing bias, while When the two-processing mode is selected, the second developing bias calculation processing (steps S321, S322, S302) is executed to determine the optimum developing bias. Hereinafter, each will be described separately.

B-1-1. First Development Bias Calculation Process (First Processing Mode) In the first development bias calculation process, as shown in FIG. 4, all colors (yellow (Y), cyan (C), magenta (M) in this embodiment) are processed. , 4 colors of black (K) are set to form a patch image (step S311), the process proceeds to step S312, and the developing bias is gradually increased in a relatively wide range and at a relatively wide interval. While changing, a plurality of patch images are formed, and the developing bias necessary for obtaining the optimum image density is tentatively obtained based on the density of each patch image. The processing content will be described in detail with reference to FIGS. 5 and 6.

FIG. 5 is a flow chart showing the contents of the bias calculation processing in the wide range of FIG. In addition, FIG.
FIG. 6 is a schematic diagram showing the processing content of FIG. 5 and the content of bias calculation processing in a narrow range described later. In this calculation process, the color for creating the patch image is set to the first color, for example, yellow (step S312a). And
With the default value of the charging bias set in advance in step S2,
In addition, the developing bias is set in four steps at relatively wide intervals (first interval) within the wide range (step S312).
b). 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 generating unit 125 is set as a wide range, and 4 out of the wide range (Vb01 to Vb10) are set. Point Vb0
1, Vb04, Vb07, Vb10 are set as the developing bias. Thus, in this embodiment, the first interval W1
Is W1 = Vb10-Vb07 = Vb07-Vb04 = Vb04-Vb01.

Four yellow solid images (FIG. 7) are sequentially formed on the photosensitive member with such a bias setting, and then, as shown in FIG.
As shown in (a), these are transferred to the outer peripheral surface of the intermediate transfer belt 41 in a predetermined arrangement order to form a first patch image PI1 (step S312c).

In the next step S312d, it is determined whether or not patch images have been created for all patch creation colors, and while the determination is "NO", the patch creation color is set to the next color (step S312e). ), Step S312
b and S312c are repeated, and as shown in FIGS. 8B to 8D, cyan (C), magenta (M), and black (K).
In this order, the first patch image PI1 is further formed on the outer peripheral surface of the intermediate transfer belt 41.

On the other hand, if "YES" is determined in the step S312d, 16 (= 4 types × 4 colors) patch images P
The image density of I1 is measured by the patch sensor PS (step S312f). In this embodiment, after the patch image PI1 is formed for all patch creation colors, the image density of the patch image PI1 is measured in order from the patch image at the head position (in this embodiment, the black (K) patch image). However, the image density of the patch image PI1 may be sequentially measured each time the patch image PI1 of each patch creation color is formed. This point is the same in the bias calculation processing (FIGS. 9, 10, 12, 13, 16 and 17) described later.

Following this, the developing bias corresponding to the target density is obtained in step S312g, 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 developing bias corresponding to the image density may be set as the provisional bias, and when the measurement result does not match, the developing bias shown in FIG.
As shown in, data D (Vb04), D sandwiching the target density
The provisional bias can be obtained by linear interpolation or averaging processing based on (Vb07).

When the provisional bias is obtained in this way, FIG.
Bias calculation processing (1) in the narrow range is executed. FIG. 9 is a flowchart showing the content of the bias calculation process (1) in the narrow range of FIG. In this calculation process, similarly to 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 charging bias is the default value set in advance in step S2, and the charging bias is set in step S31.
Within the narrow range including the provisional bias obtained in step 2, the developing bias is set in four steps at intervals (second intervals) narrower than the first interval W1 (step S313b). For example, in this embodiment, the variable band of the developing bias (Vb01 to Vb
About 1/3 of 10) is set as a narrow range, and the provisional bias is the developing bias Vb05, as shown in FIG. 6B.
If it is between Vb06, four points Vb04, Vb05, Vb06,
Vb07 is set as the developing bias ((c) in the same figure). Thus, in this embodiment, the second interval W
2 is W2 = Vb07-Vb06 = Vb06-Vb05 = Vb05-Vb04.

Four yellow solid images (FIG. 7) are sequentially formed on the photoconductor with such bias setting, and further, FIG.
As shown in (a), these are transferred to the outer peripheral surface of the intermediate transfer belt 41 to form a first patch image PI1 (step S313c). Then, the previous calculation process (step S
Similarly to (312), the patch creation color is set to the next color until it is determined in step S313d that patch images have been created for all patch creation colors (step S313).
e) and steps S313b and S313c are repeated to sequentially print the first patch image PI1 on the outer peripheral surface of the intermediate transfer belt 41 in the order of cyan (C), magenta (M), and black (K).
Will be further formed.

Thus, when 16 (= 4 types × 4 colors) patch images PI1 are formed on the intermediate transfer belt 41, the patch images at the leading position (in this embodiment, black (K) patch images) are sequentially ordered. Then, the image density of the patch image PI1 is measured by the patch sensor PS (step S31).
3f). Subsequent to this, the developing bias corresponding to the target density is obtained in step S313g. Here, when the measurement result (image density) matches the target density, the development bias corresponding to the image density may be set as the provisional bias. As shown, data D (Vb05), D (Vb06) sandwiching the target density
The optimum developing bias can be obtained by linear interpolation or the like.

Then, when the optimum developing biases have been obtained for all patch creation colors, the process proceeds to step S302, and the optimum developing biases obtained as described above are set to R.
It is stored in the AM 127, read from the RAM 127 at the time of calculating a charging bias to be described later and in a normal image forming process, and set as the developing bias.

As described above, in the first developing bias calculation processing (first processing mode), the developing bias necessary for obtaining the image of the target density in the wide range and at the first interval W1 is tentatively obtained. In addition, the developing bias necessary to obtain the target density is determined by setting the developing bias in a narrow range including the provisional bias 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.

For example, when the main power source of the image forming apparatus main body is turned on, the state of the engine section E cannot be predicted at all as described above. Therefore, it is optimal while changing the developing bias in the entire developing bias variable region. It is necessary to determine the developing bias. Therefore, it is also possible to divide the developing bias variable band (Vb01 to Vb10) into a plurality of narrow ranges and execute the same process as the bias calculation process (1) in each of the narrow ranges to obtain the optimum developing 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. On the contrary, 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 decreases. Another problem arises in that the image density cannot be accurately adjusted to the target density.

On the other hand, in the present embodiment, the bias calculation processing in the wide range as described above (step S31).
Since the approximate developing bias is tentatively obtained in 2), the developing bias is changed in a narrow range near the tentative bias and at a fine interval (second interval) W2 to calculate the optimum developing bias. As compared with the comparative example, the optimum developing bias can be obtained with high accuracy in a short time.

Further, the toner amount with respect to the developing bias, that is, the developing γ characteristic showing the change of the image density greatly changes according to the environmental condition, the endurance condition and the like, and is non-linear. The (first processing mode) has excellent effects described below.

FIG. 18 is a graph showing a typical example of the development γ characteristic. As shown in the figure, even if the image forming apparatus has the development γ characteristic A under a certain environmental condition, when the environmental condition changes, the development γ characteristic of the image forming apparatus changes according to the change. Development γ from the first development γ characteristic A
It changes to characteristic B. In particular, the inclination of the development γ characteristic is easily affected by environmental conditions and the like, and the inclination changes greatly.

Therefore, when the optimum developing bias of the image forming apparatus is the value Vb (A) in the case of the development γ characteristic A, the development γ characteristic B changes due to a slight change in environmental conditions. The optimum developing bias greatly changes to the value Vb (B). Therefore, in consideration of such a development γ characteristic, it is necessary to inevitably 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 found to be more suitable.

Furthermore, the effect becomes more remarkable in the image forming apparatus using the non-magnetic one-component toner among various toners. The reason will be described in detail below. In consideration of controllability of toner temperature with respect to carrier and the like, a non-magnetic single component toner has been adopted in recent years. The image forming apparatus using the one-component toner is characterized in that the charge amount of the toner easily changes depending on the environment and the durability condition, as compared with the image forming apparatus using the two-component toner. Because the two-component toner has a large contact area with the carrier mixed with the toner, the charge amount is relatively stable, whereas the one-component toner does not have a carrier for controlling the charge amount. This is because the toner is charged only by the charging mechanism inside the developing device, and the contact area between this 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 a non-magnetic single component toner.

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. Even in this case, the usefulness of the present invention becomes remarkable. What is more, this external additive is also easily affected by the environment, and when the amount of this external additive is 1.5% or more, the effect is apparent and the change of the development γ characteristic due to the change of environmental conditions is large. Therefore, it can be said that it is even more preferable to apply the present invention to an image forming apparatus using such toner. In addition,
An image forming apparatus adopting an intermediate transfer system, such as the image forming apparatus according to the present embodiment, is required to have improved transferability, and as a result, the amount of the external additive is also different. It tends to be larger than that of the above, and it can be said that the usefulness of the present invention is exerted also in that respect.

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 single component and contains 1.5% or more of an external additive, it is possible to obtain excellent effects. That is, the effect that 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 higher accuracy and efficiency becomes more remarkable.

B-1-2. Second Development Bias Calculation Processing (Second Processing Mode) By the way, in this embodiment, step S301 of FIG.
When the second processing mode is selected in, the second developing bias calculation processing is executed to determine the optimum developing bias. This is as described above in the judgment criteria (2), (3) and (5). This is because, in such a case, the state change of the engine section E is estimated to be small. That is, the optimum charging bias and the optimum developing bias change depending on the fatigue of the photoconductor and the toner, the change over time, and the like, but the changes have a certain degree of continuity. Therefore, the above criteria (2), (3) and
In the case of (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 developing bias calculation processing (step S3) according to this embodiment, when it is determined that the above judgment criteria (2), (3) and (5) are satisfied, the processing is simplified as follows, and the processing is accurate. The optimum developing bias is calculated.

In this second developing bias calculation processing, patch images are formed for all colors (four colors of yellow (Y), cyan (C), magenta (M) and black (K) in this embodiment). After setting the effect (step S321), the process proceeds to step S322 to execute the bias calculation process (2) in the narrow range to obtain the optimum developing bias without obtaining the provisional bias. Hereinafter, the processing content will be described with reference to FIG.

FIG. 10 is a flow chart showing the contents of the bias calculation process (2) in the narrow range of FIG. Further, FIG. 11 is a schematic diagram showing the processing contents of FIG.
This calculation processing is largely different from the bias calculation processing (1) in the narrow range described above, in the calculation processing (1) of FIG.
While four types of developing bias in a narrow range including the provisional bias are set (step S313b), in this bias calculation process (2), the bias is obtained by the immediately preceding image density measurement and stored in the RAM 127. The optimal charging bias is set as the charging bias and
This is the point that four types of developing bias in a narrow range including the optimum developing bias stored in the AM 127 are set (step S322b), and the other configurations are the same. Therefore, the description of the same configuration is omitted here.

As described above, in the second processing mode, without obtaining the provisional bias, the immediately preceding image density measurement result (previous optimum developing bias) is used in a narrow range and four types of developing bias at the second interval. Is set and the patch image of each color is formed to obtain the optimum developing bias, the first processing mode (step S312 + step S3).
In contrast to 13), the optimum developing bias can be obtained in a shorter time.

Further, the prior art (Japanese Patent Laid-Open No. 10-23992)
In contrast to the technique described in Japanese Patent Publication No. 4), there is a unique effect that the optimum developing bias can be obtained with high accuracy. The reason will be described. In the conventional technique, three sets of developing bias and charging bias are stored in advance, and a patch image is formed by these three developing biases. Therefore, in order to cover the range in which the developing bias can be changed, that is, the range approximately equal to the developing bias variable band, the three developing biases must be set at relatively wide intervals.

On the other hand, in this embodiment, the developing bias is changed within a narrow range including the optimum developing bias immediately before in the developing bias variable band (Vb01 to Vb10), and the developing bias variable band Approximately 1/3 is required, and the developing bias interval (second interval) is narrower than in the conventional technique. As a result, the optimum developing bias can be calculated with higher accuracy. It should be noted that if the range in which the developing bias is changed is simply narrowed, the optimum developing bias to be obtained is out of the range, and it is difficult to accurately calculate the optimum developing bias. Since the narrow range is set around the developing bias, the probability of occurrence of such a problem is extremely low.

The optimum developing bias thus obtained is rewritten with the optimum developing bias already stored in the RAM 127 and updated to the latest one (step S302 in FIG. 4). Then, returning to FIG. 3, the optimum developing bias calculated as described above is read from the RAM 127 and set as the developing bias. After that, the optimum charging bias is calculated (step S5) and set as the charging bias (step S6).

B-2. Optimal Charging Bias Calculation Process FIG. 12 is a flowchart showing the contents of the charging bias calculation process of FIG. In this charging bias calculation process (step S5), similarly to the case of the development bias calculation process, first, the third processing mode is set according to the operating condition of the apparatus.
Then, one of the fourth processing modes is selected (step S501). In the third processing mode, a plurality of patch images are formed while changing the charging bias within a narrow range (about 1/3 of the variable area) including a preset default value as described later, and the density of each patch image is changed. The charging bias necessary to obtain the optimum image density is determined based on the above, and is suitable when the state of the engine section 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 range) including the previous optimum charging bias. It is suitable when the state of the part E changes little. In this embodiment, the specific selection judgment in step S501 is executed based on the following criteria.

(1) When the power is turned on → the third processing mode When the power is turned on, the state of the engine section E cannot be predicted at all, so a narrow range including preset default values (about 1/3 of the variable range) The optimum charging bias is determined while changing the charging bias in ().

(2) When returning from sleep and the sleep time is less than the predetermined time → In the case of returning from the fourth processing mode sleep, the state of the engine section E may have changed greatly, When the time is short, it is estimated that the state change of the engine section E is small. Therefore, the optimum charging bias is changed while changing the charging bias within the narrow range (about 1/3 of the variable region) including the optimum charging bias of the previous time. To decide.

(3) Fixing unit 5 when returning from sleep
If the fixing temperature is higher than a predetermined temperature → In the case of returning from the fourth processing mode to the sleep state, the state of the engine section E may have changed significantly. When the temperature is maintained at a high temperature, the state change of the engine section E is estimated to be small, so the narrow range including the optimum charging bias of the previous time (about 1 / of the variable range)
The optimum charging bias is determined while changing the charging bias in 3).

(4) At the time of returning from sleep (excluding the cases (2) and (3) above) → third processing mode Except for (2) and (3) described above, the state of the engine section E is at the time of returning from sleep. Since there is a possibility that the charging bias has changed significantly, 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.

(5) At the time of continuous image formation → fourth processing mode When image formation is continuously performed, the state of the engine section E is unlikely to change significantly from the time of the last density adjustment. The optimum charging bias is determined while changing the charging bias within a narrow range (about 1/3 of the variable region) including the optimum charging bias of.

When the third processing mode is selected based on the above judgment criteria, the first charging bias calculation processing (steps S511, S512 and S502) is executed to determine the optimum charging bias, while When the four processing mode is selected, the second charging bias calculation processing (steps S521, S522, S502) is executed to determine the optimum charging bias. Hereinafter, each will be described separately.

B-2-1. First Charging Bias Calculation Processing (Third Processing Mode) In the first charging bias calculation processing, as shown in FIG.
After setting the patch images for all colors (four colors of yellow (Y), cyan (C), magenta (M), and black (K) in this embodiment) (step S511), Proceeding to step S512, a plurality of patch images are formed while changing the charging bias in four steps at relatively narrow intervals within a narrow range including a preset default value, and forming each patch image. The charging bias necessary to obtain the optimum image density is obtained based on the density of the. Hereinafter, the details of the processing will be described with reference to FIG.
~ It demonstrates, referring to FIG.

FIG. 13 is a flowchart showing the contents of the processing in step S512, that is, the contents of the bias calculation processing (3) in the narrow range of FIG. Also, FIG.
4 is a schematic diagram showing the processing contents of FIG. In this calculation process, the color for creating the patch image is set to the first color, for example, yellow (step S512a). And
The charging bias is set in four stages at relatively narrow intervals (third intervals) within the narrow range including the default value set in step S2 in advance (step S512b). As described above, the charging bias calculation process is different from the developing bias calculation process without performing the calculation process in a wide range.
Only the calculation process in the narrow range is executed. 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 preset value or the optimum charging bias immediately before is set as shown in FIG. When the charging bias is between Va05 and Va06,
Four points Va04, Va05, Va06, Va07 are set as the charging bias. Thus, in this embodiment, the third interval W3 is W3 = Va07-Va06 = Va06-Va05 = Va05-Va04.

When four types of charging biases are set for the yellow color as described above, the halftone image of each yellow (FIG. 15) is formed on the photoconductor while gradually increasing the charging bias from the lowest value Va04. These are sequentially formed on the upper surface, and these are transferred to the outer peripheral surface of the intermediate transfer belt 41 to form the second patch image PI2 (FIG. 8A: step S512c).

In the next step S512d, it is determined whether or not the second patch image has been created for all the patch creation colors, and while the judgment is "NO", the patch creation color is set to the next color ( Step S512e), Step S512
Repeat b to S512d, as shown in FIGS. 8B to 8D, cyan (C), magenta (M), and black (K).
In this order, the second patch image PI2 is further formed on the outer peripheral surface of the intermediate transfer belt 41.

On the other hand, if "YES" is determined in the step S512d, 16 (= 4 types × 4 colors) patch images P
The image density of I2 is measured by the patch sensor PS (step S512f). In addition, following this, step S51
The charging bias corresponding to the target density is calculated with 2 g. 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. If they do not match, the charging bias shown in FIG. As shown in, data D (V
The optimum charging bias can be obtained by linear interpolation based on a05) and D (Va06).

When the optimum charging bias is obtained for all patch creation colors, the process proceeds to step S502,
The optimum charging bias obtained as described above is stored in the RAM.
127, RAM in the normal image forming process
It is read from 127 and set as the charging bias.

B-2-2. Second Charging Bias Calculation Processing (Fourth Processing Mode) In this embodiment, if the fourth processing mode is selected in step S501 of FIG. 12 for the same reason as in the case of the developing bias calculation processing, the second charging bias calculation processing is performed. Is executed to determine the optimum charging bias.

In this second charging bias calculation processing, patch images are formed for all colors (four colors of yellow (Y), cyan (C), magenta (M), and black (K) in this embodiment). After setting the effect (step S521), the process proceeds to step S522 to execute the bias calculation process (4) in the narrow range to obtain the optimum charging bias (step S522).

FIG. 16 is a flow chart showing the contents of the bias calculation process (4) in the narrow range of FIG. This calculation process is largely different from the bias calculation process (3) in the narrow range described above, in the calculation process (3) in FIG. 13, four types of charging in the narrow range based on a predetermined value of the charging bias. Bias is set (step S51
In contrast to 2b), in the bias calculation process (4), four types of charging bias in a narrow range are set based on the charging bias stored in the RAM 127 obtained by the immediately preceding image density measurement (step). S515b)
The other points are the same as each other. Therefore, the description of the same configuration is omitted here.

When the optimum charging bias is obtained for all patch creation colors, the process proceeds to step S502,
The optimum charging bias obtained as described above is stored in the RAM.
127, RAM in the normal image forming process
It is read from 127 and set as the charging bias.

B-3. Effects of the Embodiment As described above, according to this embodiment, the first and second processing modes are prepared in advance in order to determine the optimum developing bias, and the first processing mode or the second processing mode is set in accordance with the operating condition of the apparatus. Since the second processing mode is selectively executed, the most suitable processing mode can be selected and executed according to the operating condition, and the development bias, which is one of the density control factors, is efficient and highly accurate. The optimum value of can be determined.

The same applies to the charging bias. That is, since the third and fourth processing modes are prepared in advance in order to determine the optimum charging bias, and the third processing mode or the fourth processing mode is selectively executed according to the operating condition of the apparatus, The most appropriate processing mode can be selected and executed according to the operating condition, and the optimum value of the charging bias, which is one of the concentration control factors, can be determined efficiently and with high accuracy.

C. In addition, 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 above embodiment, in the case of the judgment criteria (2), (3) and (5), the second change is based on the expectation that the state change of the engine section E is small.
Although it is configured to selectively execute the processing mode,
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 properly deal with such a case, as shown in FIG. 17, in the second processing mode,
It is determined that the optimum development bias cannot be calculated for all patch creation colors (step S323).
Then, the process may proceed to step S312 to further execute the first processing mode. By doing so, even when the state of the engine section E (image forming means) is greatly changed, the optimum developing bias can be determined flexibly and accurately.

Further, in the above embodiment, about 1/3 of the variable band (Vb01 to Vb10) of the developing bias is set as the narrow range, but the width of the narrow range is not limited to this. If the width is wide, the significance of using the narrow range is diminished and the calculation accuracy of the optimum developing bias is lowered. Therefore, it is necessary to set the developing bias variable band to about 1/2 or less. Further, although the narrow ranges in the first and second processing modes have the same width, the same range is not an essential requirement and may be set to be different from each other. The same applies to the narrow range of the charging bias.

In the above embodiment, the image forming apparatus is capable of forming a color image using four color toners. However, the application of the present invention is not limited to this, and a monochrome image is formed. Of course, the present invention can be applied to an image forming apparatus that forms only an image. The image forming apparatus according to the above-described embodiment is a printer that forms an image given from an external device such as a host computer via the interface 112 on a sheet such as copy paper, transfer paper, paper, and OHP transparent sheet. However, the present invention can be applied to all electrophotographic image forming apparatuses such as copying machines and facsimile machines.

In the above embodiment, the toner image on the photoconductor 21 is transferred to the intermediate transfer belt 41, the toner image is used as a patch image to detect the image density, and the optimum developing bias is determined based on the detection result. And the optimum charging bias is calculated, but the toner image is not on the transfer medium other than the intermediate transfer belt (transfer drum, transfer belt, transfer sheet, intermediate transfer drum, intermediate transfer sheet, reflective recording sheet or transmissive recording sheet, etc.). The present invention can also be applied to an image forming apparatus that transfers a patch to form a patch 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 the optimum charging bias may be calculated based on the above.

Further, in the above embodiment, the optimum values of the developing bias and the charging bias are calculated as the density control factors. However, when the optimum value of only one of them is calculated, other density such as the transfer bias and the exposure amount is calculated. The present invention can be applied to the case of obtaining the optimum value of the control factor.

[Brief description of drawings]

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.

FIG. 3 is a flowchart showing a density adjustment operation in the image forming apparatus of FIG.

FIG. 4 is a flowchart showing the contents of the developing bias calculation process of FIG.

5 is a flowchart showing the content of bias calculation processing in the wide range of FIG. 4. FIG.

FIG. 6 is a schematic diagram showing the processing content of FIG. 5 and the content of bias calculation processing in a narrow range described later.

FIG. 7 is a diagram showing a first patch image.

FIG. 8 is a diagram showing a formation order of patch images.

FIG. 9: Bias calculation processing (1) in the narrow range of FIG.
It is a flowchart which shows the content of.

10 is a flowchart showing the contents of a bias calculation process (2) in the narrow range of FIG.

FIG. 11 is a schematic diagram showing the processing contents of FIG.

FIG. 12 is a flowchart showing the contents of the charging bias calculation process of FIG.

FIG. 13 is a flowchart showing the contents of bias calculation processing (3) in the narrow range of FIG.

FIG. 14 is a schematic diagram showing the processing content of FIG.

FIG. 15 is a diagram showing a second patch image.

16 is a flowchart showing the contents of a bias calculation process (4) in the narrow range of FIG.

FIG. 17 is a diagram showing another embodiment of the image forming method according to the present invention.

FIG. 18 is a graph showing changes in development γ characteristics with changes in environmental conditions and the like in the image forming apparatus of FIG. 1.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Control unit (control means), 11 ... Main controller (control means), 12 ... Engine controller (control means), 111 ... CPU (control means), 123 ... CPU
(Control means) 127 ... RAM (storage means), E ... engine section (image forming means)

Continued front page    F-term (reference) 2H027 DA09 DA12 DA40 DE02 DE09                       EA01 EA05 EC03 EC06 EC07                       EC08 EC09 EC18 EC20 EE08                       EF01 EF06 EF09 FB15 FB19                       FC03                 5C074 AA02 BB17 DD01 DD16 EE03                       EE06 EE11

Claims (6)

[Claims] 1. An image forming apparatus for optimizing a density control factor affecting image density at a predetermined timing, wherein the density control factor is optimized by a plurality of steps.
And the second processing mode for optimizing the concentration control factor with the number of steps smaller than the number of steps in the first processing mode can be selectively executed. An image forming apparatus, which selectively executes the second processing mode when continuous image formation is being performed. 2. The image forming apparatus according to claim 1, wherein the step counted in the step number includes a step of forming a patch image. 3. A storage means for storing the optimum value of the density control factor each time the density control factor is optimized, wherein the second processing mode is optimized by the processing mode executed immediately before. The image forming apparatus according to claim 1, wherein the density control factor is optimized based on the optimum value stored in the storage unit. 4. An image forming apparatus for setting a density control factor that affects image density to an optimum value at a predetermined timing, and when the predetermined timing is during continuous image formation, the optimum value set immediately before is set. While forming the density control factor on the basis of the value, when the predetermined timing is not during continuous image formation, the density control factor is set regardless of the immediately preceding optimum value. apparatus. 5. An image forming method for optimizing a density control factor affecting image density, wherein the density control factor is selected in a plurality of steps as a processing mode for optimizing the density control factor affecting image density. A first processing mode for optimizing and a second processing mode for optimizing the density control factor with a smaller number of steps than the number of steps in the first processing mode are provided, and during continuous image formation, An image forming method, characterized in that the second processing mode is executed. 6. An image forming method for setting a density control factor that affects image density at a predetermined timing to an optimum value, the method comprising: determining whether or not the predetermined timing is during continuous image formation. When the image is being formed, the density control factor is set based on the optimum value that was set immediately before, while when the predetermined timing is not during continuous image formation, it has nothing to do with the immediately preceding optimum value. And the step of setting the density control factor.