JP2002214852A - Image forming apparatus and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus and image forming method, whereby toner image density is easily and securely stabilized over a wider range of density. SOLUTION: Solid patch images are formed under various patch-forming conditions (E, Vb). Thereafter, the optical density of each solid patch image is measured by a patch sensor to extract a patch-forming condition that matches a target high density (OD=1.2) as 'high density correlation data'. In addition, line patch images are formed under various patch-forming conditions (E, Vb), thereafter, the optical density of each line patch image is measured by the patch sensor in order to extract a patch-forming condition that matches a target low density (OD=0.2) as 'low density correlation data'. Then, they are set as the optimum exposure energy and the optimum development bias, based one of correlation data (E2, Vb(3)) belonging to a set of products of the high- density correlation data and low-density correlation data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming an electrostatic latent image by exposing a surface of a photoreceptor with a light beam to form an electrostatic latent image and then visualizing the electrostatic latent image with toner to form a toner image. The present invention relates to a forming apparatus and an image forming method.

[0002]

2. Description of the Related Art In an image forming apparatus of this type, the image density of a toner image varies due to individual differences of the apparatus, fatigue and aging of the photoconductor and toner, and changes in temperature and humidity around the apparatus. There is. Therefore, a technique for obtaining the optimum values of the charging bias and the developing bias, that is, the optimum charging bias and the optimum developing bias, and stabilizing the image density by setting the charging bias and the developing bias to the optimum charging bias and the optimum developing bias, respectively, has conventionally been achieved. Has been proposed. For example, in the invention described in JP-A-10-239924, a predetermined toner image is formed as a patch image on a photoconductor while changing a charging bias and a developing bias, and the image density of each reference patch is measured. . Based on these measured values, the optimal charging bias and developing bias for obtaining the target densities, that is, the low-density target densities and the high-density target densities in two gradations are determined.

[0003]

However, when a plurality of patch images are formed while changing the charging bias, the light attenuation characteristics of the photoreceptor fluctuate in conjunction with the change in the charging bias, and the light portion potential changes significantly. Therefore, for example, the optimum developing bias for obtaining the high-density side target density can be obtained, but the optimum developing bias for obtaining the low-density side target density cannot be obtained in some cases. In addition, the reverse case also occurred. As described above, in the conventional apparatus that pays attention to the charging bias and the developing bias as the density adjustment factors for adjusting the image density of the toner image, it is difficult to stabilize the image density of the toner image over a wide density range. I was

An object of the present invention is to provide an image forming apparatus and an image forming method capable of easily and reliably stabilizing the image density of a toner image over a wide density range. Aim.

[0005]

In order to achieve the above object, an image forming apparatus according to the present invention comprises: an exposing means for exposing and scanning a surface of a photoreceptor with a light beam to form an electrostatic latent image;
Developing means for visualizing the electrostatic latent image with toner to form a toner image; a toner image formed by the developing means by optimizing exposure energy of the light beam and a developing bias applied to the developing means Control means for controlling the image density of the low-density target density, the control means comprising: low-density correlation data between exposure energy and a developing bias for forming a toner image at a low-density target density; One correlation data belonging to the intersection of the exposure energy for forming a toner image at the higher density target density higher than the density and the high density side correlation data with the developing bias is set as the optimal exposure energy and the optimal developing bias. The configuration is such that the exposure energy and the developing bias are optimized.

Further, the image forming method according to the present invention comprises:
The electrostatic latent image is formed by exposing and scanning the surface of the photoreceptor with a light beam at an optimal exposure energy, and the electrostatic latent image is visualized with toner while applying an optimal developing bias to a developing unit, thereby forming a toner image. In order to achieve the above object, the correlation data between the exposure energy and the developing bias required to form a toner image at the low density target density is obtained as the low density correlation data. A first step of obtaining correlation data between exposure energy and a developing bias required to form a toner image at a higher density target density higher than the lower density target density, as high density side correlation data; Two steps, a third step of obtaining a product set of the low-density side correlation data and the high-density side correlation data, and an exposure energy constituting one correlation data belonging to the product set And a fourth step of setting over and the developing bias respectively as the optimum exposure energy and the optimal development bias.

In the invention (image forming apparatus and image forming method) configured as described above, low-density-side correlation data required for forming a toner image at a low-density-side target density is obtained.
After calculating the high-density correlation data necessary for forming a toner image at the high-density target density, the intersection of the low-density correlation data and the high-density correlation data is determined, and then the intersection is calculated. Are set as the optimum exposure energy and the optimum developing bias, respectively. Therefore, since the image density of the toner image is controlled to the target density at two points of high density and low density, the image density of the toner image is reliably guaranteed over a wide density range, and the image stability is improved.

Further, in the present invention, the exposure energy and the developing bias are employed as the density adjusting factors for adjusting the image density of the toner image. Since there is no change, the exposure energy and the developing bias can be optimized simply by obtaining the intersection of the low-density side correlation data and the high-density side correlation data as described above.

Here, each correlation data may be obtained based on (1) the light attenuation characteristic of the photosensitive member and the development γ characteristic of the developing means, or (2) so-called patch sensing. In particular, in the case of the former (1), the optimum exposure energy and the optimum developing bias are obtained before the actual image forming processing, for example, at the time of completion of the assembly of the apparatus or before shipment from the factory, based on the previously obtained correlation data, and the memory and the like are obtained. It may be stored in a storage unit. Further, when the image forming process is repeated, for example, the film thickness of the photoconductor may decrease and the light attenuation characteristics of the photoconductor may fluctuate depending on the operation state of the apparatus. It is preferable that the exposure energy and the optimum developing bias are obtained in advance, and the optimum exposure energy and the optimum developing bias are stored in the storage unit in association with the photoconductor film thickness. That is, the film thickness of the photoconductor is obtained at an appropriate timing, the exposure energy and the developing bias corresponding to the photoconductor film thickness are read out from the storage unit, and are set as the optimum exposure energy and the optimum developing bias, respectively. The image density of the toner image can always be maintained at the target density irrespective of the operation state of the forming apparatus (for example, the operation time and the number of printed sheets), and higher stability can be obtained.

If the light attenuation characteristic of the photoreceptor is known in advance, the known data may be used. However, the light attenuation characteristic is measured using a surface potential measuring means for measuring the surface potential of the photoreceptor. May be measured. That is, while changing the exposure energy of the light beam in multiple steps, an electrostatic latent image is formed at each exposure energy, and the surface potential of the electrostatic latent image is obtained by the surface potential measuring means, and the light attenuation of the photoconductor is reduced. Characteristics may be obtained.

[0011] The development γ characteristic of the developing means is also
If it is known in advance, the known data may be used, but the development γ characteristic may be actually measured by so-called patch sensing. That is, a density measuring unit for measuring the image density of the toner image is provided, and while the developing bias is changed and set in multiple steps, the toner image is formed as a patch image with each developing bias, and the image density of the patch image is measured by the density measuring unit. To obtain the development γ characteristic.

On the other hand, when the low-density side correlation data and the high-density side correlation data are obtained by patch sensing,
Density measuring means for measuring the image density of the toner image formed on the photoreceptor or the image carrier is further provided, and the control means derives the correlation data as follows.
While changing and setting the combination of the exposure energy and the developing bias in multiple steps, the first toner image is formed as a high-density patch image in each combination, and the image density of the high-density patch image is obtained by a density measuring unit. The combination when the image density substantially matches the high-density target density is used as the high-density correlation data. On the other hand, the combination of the exposure energy and the developing bias is changed and set in multiple steps, and each combination is more than the first toner image. A low-density second toner image is formed as a low-density patch image, and the image density of the low-density patch image is obtained by a density measuring unit, and a combination when the image density substantially matches the low-density target density is determined. The low-concentration side correlation data is used.

Here, as the high-density patch image, an image having a dot area ratio of about 80% or more with respect to the entire patch image can be used. On the other hand, a halftone image can be used as the low-density patch image. Further, the halftone image is composed of a plurality of one-dot lines that are spaced apart from each other, and the plurality of one-dot lines are substantially parallel to each other, and furthermore, one-dot lines adjacent to each other are arranged. It is preferable to adopt one that is separated by n line intervals (an integer of n ≧ 5).

Incidentally, the optimum exposure energy obtained as described above may be out of the variable range of the exposure energy, or the optimum developing bias obtained as described above may be out of the variable range of the developing bias. . In such a case, it is effective means to change the light attenuation characteristic of the photoconductor by changing and setting the charging bias applied to the charging means. That is, after the charging bias is changed and set, the optimum exposure energy and the optimum developing bias may be updated by optimizing the exposure energy and the developing bias with the charging bias. This makes it possible to keep the optimum exposure energy and the optimum developing bias within the variable range.

When the charging bias is changed and set as described above, the charging bias may be changed arbitrarily. However, the charging bias may be out of the upper limit of the variable range or may be out of the lower limit of the variable range. It is possible to more reliably and quickly set the optimum exposure energy and the optimum developing bias in the variable range by determining whether the charging bias has occurred and changing and setting the charging bias according to the determination result.

A bias in which a DC component and an AC component are superimposed may be given to the developing means as a developing bias.
In this case, the optimum developing bias is adjusted by controlling at least one of the DC component, the peak-to-peak voltage of the AC component, the ratio of the high potential period to the low potential period in one cycle of the AC component, and the frequency of the AC component. be able to.

[0017]

DETAILED DESCRIPTION OF THE INVENTION First Embodiment FIG. 1 is a diagram showing a first 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 includes yellow (Y), cyan (C), magenta (M),
The apparatus forms a full-color image by superimposing four black (K) toners, or forms a monochrome image using only black (K) toner. 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 EG according to a command from the main controller 11. Thus, an image corresponding to the image signal is formed on the sheet S.

In the engine section EG, the photosensitive member 2 is provided rotatably in the direction of arrow D1 in FIG. A charging unit 3 as a charging unit, a rotary developing unit 4 as a developing unit, and a cleaning unit 5 are arranged around the photoreceptor 2 along the rotation direction D1. The charging unit 3 includes a charging bias generator 1
A charging bias is applied from 21 to uniformly charge the outer peripheral surface of the photoconductor 2.

Then, a light beam L is emitted from the exposure unit 6 toward the outer peripheral surface of the photosensitive member 2 charged by the charging unit 3. As shown in FIG. 2, the exposure unit 6 is electrically connected to the image signal switching unit 122, and the exposure power control unit 123 controls the exposure power in accordance with the image signal given through the image signal switching unit 122. The unit 6 is controlled to scan and expose the light beam L on the photosensitive member 2 to form an electrostatic latent image on the photosensitive member 2 corresponding to an image signal.
For example, based on a command from the CPU 124 of the engine controller 12, when the image signal switching unit 122 is conducting with the patch creation module 125, the patch image signal output from the patch creation module 125 is sent to the exposure power control unit 123. And a patch latent image is formed.
On the other hand, the image signal switching unit 122
When the CPU 111 is electrically connected to the CPU 111, the light beam L is scanned and exposed on the photosensitive member 2 in response to an image signal provided from an external device such as a host computer via the interface 112, and a static image corresponding to the image signal is provided. An electrostatic latent image is formed on the photoconductor 2.

The electrostatic latent image thus formed is developed by the developing unit 4 with toner. That is, in this embodiment, the developing unit 4 is used as the developing unit 4 for black.
K, a developing device 4C for cyan, a developing device 4M for magenta,
And a developing unit 4Y for yellow is rotatably provided about the axis. Then, these developing units 4K, 4C, 4
M and 4Y are rotationally positioned and selectively abutted against the photoconductor 2 or positioned at a separated position.
The developing bias of the DC component is applied by the developing bias generator 126 to apply the toner of the selected color to the surface of the photoconductor 2. As a result, the electrostatic latent image on the photoconductor 2 is visualized in the selected toner color.

The toner image developed by the developing unit 4 as described above is transferred to the transfer unit 7 in the primary transfer area TR1.
Is primarily transferred onto the intermediate transfer belt 71. In the vicinity of the primary transfer area TR1, the intermediate transfer belt 7
A patch sensor PS is disposed as a “density measuring unit” of the present invention, facing the surface of the first transfer belt 1, and measures the optical density of a patch image formed on the outer peripheral surface of the intermediate transfer belt 71 as described later. Further, the primary transfer region TR1
At a position in the circumferential direction (rotational direction D1 in FIG. 1) from
A cleaning unit 5 is disposed to scrape off toner remaining on the outer peripheral surface of the photoconductor 2 after the primary transfer.
Also, if necessary, the photosensitive member 2
Is reset.

The transfer unit 7 includes an intermediate transfer belt 71 stretched over a plurality of rollers, and a driving unit (not shown) for driving the intermediate transfer belt 71 to rotate. When the color image is transferred to the sheet S, the toner images of each color formed on the photoconductor 2 are transferred to the intermediate transfer belt 71.
A color image is formed by superimposing the color image on the sheet S, and the color image is secondarily transferred onto the sheet S taken out of the cassette 8 in a predetermined secondary transfer area TR2. Also,
The sheet S on which the color image is formed is conveyed to the discharge tray provided on the upper surface of the apparatus main body via the fixing unit 9.

After the secondary transfer, the toner remaining on the outer peripheral surface of the intermediate transfer belt 71 after the secondary transfer is removed from the intermediate transfer belt 71 by a cleaning unit (not shown).

In FIG. 2, reference numeral 113 denotes 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 through
7 is an arithmetic program executed by the CPU 124,
Is a memory (storage means) for storing the calculation result in and the control data for controlling the engine unit EG.

Next, a description will be given of a process of optimizing a density adjustment factor executed in the image forming apparatus having the above-described configuration. In this image forming apparatus, the optimization energy shown in FIG. 3 is executed at an appropriate timing, for example, at the completion of assembly of the apparatus, before shipment from the factory, or at the time of maintenance of the apparatus. Are optimized to adjust the image density of the toner image of each color.

FIG. 3 is a flowchart showing a process of optimizing the density adjustment factor in the image forming apparatus of FIG. First, for example, at the stage of completion of the assembly of the apparatus, an operator or the like applies the light attenuation characteristic of the photoconductor 2 as shown by a solid line in FIGS. 4 and 5 to the image forming apparatus via an operation unit (not shown) such as a keyboard. input. Thereby, the control unit 1
Acquires the light attenuation characteristic and temporarily stores it in the memory 127 (step S11). Further, the operator inputs, for example, a development γ characteristic as shown in FIG. by this,
The control unit 1 acquires the development γ characteristic and temporarily stores it in the memory 127 (step S12).

Next, the CPU 124 of the control unit 1 reads out the light attenuation characteristic and the development γ characteristic from the memory 127, and obtains the correlation data between the exposure energy E and the development bias Vb for forming the toner image at the higher density target density. It is obtained as high-concentration side correlation data (step S13). In this embodiment, the optical density (O
D) = 1.2 ”, and when a solid image is formed at each exposure energy, the optical density (O
The developing bias Vb required for D) to be 1.2 is calculated. That is, as can be seen from FIG. 4, the photoconductor 2 charged by the charging unit 3 has a surface potential Vs0, and the photoconductor 2 is irradiated with the light beam L with the exposure energy E toward the solid image. Is formed, the surface potential of the latent image portion becomes the light portion potential Von.

On the other hand, in order to obtain a toner image having a target density on the high density side, a predetermined toner adhesion amount M (1.
2) (the correlation between the target density and the toner adhesion amount is known), and the contrast potential (= │ (development bias)-(photoconductor 2) corresponding to the toner adhesion amount M (1.2) is required.
Is a potential Vcon as shown in FIG.

Therefore, as shown by the alternate long and short dash line in FIG. 4, by setting the exposure energy E and the developing bias Vb so that the difference between the bright portion potential Von and the developing bias Vb becomes the contrast potential Vcon, a high density is obtained. A toner image can be formed at the side target density.
The PU 124 calculates the correlation data indicated by the one-dot chain line in FIG.

In the next step S14, correlation data (low-density correlation data) between the exposure energy E and the developing bias Vb for forming a toner image at the low-density target density is obtained. In this embodiment, “optical density (OD) = 0.2” is set as the low-density-side target density. When a line image LI of 1on5off as shown in FIG. Development bias Vb required for optical density (OD) of image to be 0.2
Is obtained by calculation. Specifically, it is obtained by executing steps S141 to S145 shown in FIG.

First, the exposure energy E is set to the minimum exposure energy Emin (step S141). Then, a latent image profile when a latent image corresponding to the line image LI in FIG. 7 is formed on the photoreceptor 2 is obtained with the exposure energy E (step S142), and then the line latent image is developed to obtain a low-density image. A developing bias for forming the line image LI having the target density is obtained (step S143) (that is, a developing bias for achieving the toner adhesion at the low-density side target density is obtained).

When the developing bias Vb corresponding to the exposure energy E is thus obtained, it is determined in step S144 whether the exposure energy E exceeds the maximum exposure energy Emax, and "NO", that is, the exposure energy E is While it is equal to or less than Emax, step S145
After the exposure energy E is incremented by the minute amount ΔE, the process returns to step S142 to return to step S14.
Step S143 is executed to determine a developing bias Vb corresponding to each exposure energy E.

Such a series of processing (step S141)
To 145), correlation data indicated by a two-dot chain line in FIG. 5 is obtained, which corresponds to the “low-concentration-side correlation data” of the present invention.

Returning to FIG. 3, the description of the optimization process will be continued.
In the next step 15, a product set of the high-density-side correlation data obtained in step S13 and the low-density-side correlation data obtained in step S14 is obtained. Specifically, as shown in FIG. 9, an intersection point CP between a one-dot chain line representing the high concentration side correlation data and a two-point difference line representing the low concentration side correlation data is obtained.
The exposure energy E and the developing bias Vb corresponding to the intersection CP are set as the optimum exposure energy and the optimum developing bias, respectively, and stored in the memory 127.

When the optimum exposure energy and the optimum developing bias for the specific toner color obtained in step S12 are obtained in this way, whether the optimum exposure energy and the optimum developing bias have been obtained for all the toner colors in step S16. Is determined, and this step S1
While determining “NO” in step 6, the processes of steps S12 to S16 are repeated for the remaining toner colors to obtain the optimum exposure energy and the optimum developing bias for each toner color, and store them in the memory 127.

The apparatus shipped from the factory and located near the user accesses the memory 127 at an appropriate timing (for example, when the apparatus is started), and obtains information on the exposure energy and the developing bias therefrom. Then, a series of image formation is performed based on the information.

As described above, according to this embodiment, the image density of the toner image is adjusted to the low-density target density (OD = 0.2) and the high-density target density (OD = 1.2) for each toner color. An image can be formed stably in a wide density range. Further, in the conventional apparatus in which the charging bias is used as the density adjustment factor, the light attenuation characteristics of the photosensitive member 2 fluctuate according to the value of the charging bias, and it has been difficult to optimize the density adjustment factor over a wide density range. On the other hand, in the present embodiment in which the exposure energy and the developing bias are used as the density adjustment factors, neither the exposure energy nor the developing bias has any effect on the light attenuation characteristics of the photoreceptor 2; The exposure energy and the developing bias can be optimized by obtaining a product set of the correlation data and the high-density-side correlation data. Therefore, according to this embodiment, the image density of the toner image can be easily and reliably stabilized over a wide density range.

B. Second Embodiment By the way, in this type of image forming apparatus, the light attenuation characteristic may fluctuate depending on the operation state of the apparatus. For example, as is well known in the art, the photoreceptor 2 has an undercoat layer, a charge generation layer, and a charge transport layer laminated in this order on a drum-shaped conductive substrate such as aluminum. Then, when the light beam L is irradiated on the photoreceptor 2, the surface charge corresponding to the irradiated portion is lost and an electrostatic latent image is formed. Taking a negatively charged OPC as an example, holes and electrons generated in the charge generation layer by light beam irradiation move according to the electric field. That is, the holes move the charge transport layer toward the photoreceptor surface so as to be attracted to the negative charges on the photoreceptor surface, and cancel the negative charges on the surface. As a result, an electrostatic latent image is formed. The light attenuation characteristic of the photoreceptor 2 is closely related to the thickness of the photoreceptor 2, particularly, the thickness of the charge transport layer. As shown in FIG. 1, since a large number of contact members such as the cleaning unit 5 are in contact with the photoreceptor 2, the film of the charge transport layer increases in accordance with an increase in the operation time of the image forming apparatus and the number of prints. The thickness decreases. Then, the electric field applied to the charge transport layer changes, which changes the mobility of the carrier, and changes the light attenuation characteristics of the photoconductor 2. Further, the light attenuation characteristics of the photoconductor 2 may fluctuate depending on factors other than the film thickness of the photoconductor 2, for example, the apparatus environment. Also, the development γ characteristic may vary greatly depending on the environment of the apparatus, particularly the influence of humidity, and the thickness of the photoconductor.

As described above, if the light attenuation characteristic and the development γ characteristic of the photosensitive member 2 fluctuate greatly depending on the use state of the image forming apparatus, the optimum exposure energy and the optimum development bias are obtained as described above depending on the use state. It may deviate from the optimal value. Therefore, as described below, assuming several use states in advance, the optimum exposure energy and the optimum developing bias in each use state are stored in the memory 12.
It is desirable to read the optimum exposure energy and the optimum developing bias corresponding to the use state in order to optimize the exposure energy and the developing bias.

The mechanical and electrical configuration of the image forming apparatus according to the second embodiment is the same as that of the first embodiment. Only a part of the developing bias setting process is different, and the other operations are the same as those of the first embodiment. Therefore, here, referring to FIG. 10 and FIG.
The description will focus on the differences from the embodiment.

FIG. 10 is a flowchart showing the process of optimizing the concentration control factor in the second embodiment. Also,
FIG. 11 is a diagram schematically showing the operation of the second embodiment. In the second embodiment, “temperature and humidity environment” and “photoconductor thickness” are set as the use conditions, and the optimum conditions (optimum exposure energy and optimum development bias) in each use condition are shown in FIG. And stores it in the memory 127 while associating it with the use state. In the column of “temperature and humidity environment” in FIG. 11, the symbols HH, NN, and LL indicate “high temperature and high humidity environment”, “normal temperature and normal humidity environment”, and “low temperature and low humidity environment”, respectively.

In the second embodiment, in the first use state, for example, in the "HH" environment and at the film thickness t1 of the photosensitive member 2, the optimum exposure energy E (H1) and the optimum development energy are obtained by the processing procedure shown in FIG. The bias Vb (H1) is obtained and stored in the memory 127 while corresponding to the use state.

First, for example, at the completion of assembly of the apparatus, an operator or the like inputs the light attenuation characteristics of the photosensitive member 2 corresponding to the use state to the image forming apparatus via an operation unit (not shown) such as a keyboard. As a result, the control unit 1 acquires the light attenuation characteristic and temporarily stores it in the memory 127 (step S17). Further, the operator inputs the development γ characteristic corresponding to the use state of the specific toner color to the image forming apparatus by using the operation unit. Thereby, the control unit 1 acquires the development γ characteristic and temporarily stores it in the memory 127 (step S18).

Next, the CPU 124 of the control unit 1 reads out the light attenuation characteristic and the development γ characteristic from the memory 127 and forms a toner image at the target density on the high density side in the same manner as in the first embodiment (FIG. 3). The correlation data between the exposure energy E and the developing bias Vb is obtained as high-density-side correlation data (step S13), and the low-density side of the exposure energy E and the developing bias Vb for forming a toner image at the low-density-side target density. Correlation data was obtained (step S1
4) Thereafter, a product set of the high-density-side correlation data and the low-density-side correlation data is obtained (step S15). In this way,
The optimum exposure energy and the optimum developing bias for the specific toner color acquired in step S12 are obtained. This process is repeated for all the toner colors to obtain the optimum exposure energy E (H1) and the optimum developing bias Vb (H1).
Is obtained and stored in the memory 127.

Next, with respect to the state of the film thickness t2 of the photoreceptor, the above-described series of processing (FIG. 10) is executed to obtain the optimum exposure energy E (H2) and the optimum developing bias Vb (H2) corresponding to each use state. Is obtained and stored in the memory 127. These operations are performed for other use states, and a data table is created in the memory 127 (see FIG. 11).

At a suitable timing (for example, when the apparatus is started up or during printing standby), the CPU 124 detects the apparatus shipped from the factory and at hand of the user by the output of a temperature / humidity sensor provided in the apparatus. Based on the temperature and humidity information and the photoreceptor film thickness estimated from data such as the total operation time and the total number of prints, the use state of the apparatus is detected, and the optimum condition corresponding to the detection result is stored in a data table ( From FIG. 11), the optimum exposure energy and the optimum developing bias are set. As described above, in the second embodiment, since the CPU 124 functions as the “film thickness deriving unit” and the “optimizing unit” of the present invention, an image is always formed with the optimum exposure energy and the optimum developing bias corresponding to the use state. And further stability of the toner image can be achieved.

In the second embodiment, the optimum exposure energy and the optimum developing bias in each use state are stored in the memory 127 assuming several use states in advance as shown in FIG. Instead of the optimum exposure energy and the optimum developing bias, the light attenuation characteristic and the development γ characteristic in each use state are stored in the memory 127, and the light attenuation characteristic and the development γ characteristic corresponding to the use state of the apparatus are stored at an appropriate timing. The optimal exposure energy and the optimal developing bias may be obtained by reading and the same processing flow as in FIG.

C. Third Embodiment In the first embodiment shown in FIG. 3 and the second embodiment shown in FIG. 10, the light attenuation characteristics of the photoconductor 2 are known in advance, and the light attenuation characteristics are determined by an operation unit such as a keyboard (not shown). The operator inputs data to the image forming apparatus through steps S11 and S17.
The optical attenuation characteristic of the photoreceptor 2 may be actually measured by executing the “light attenuation characteristic measuring process” shown in FIG. 12 instead of step S17. The mechanical and electrical configuration of the image forming apparatus according to the third embodiment is the same as that of the first embodiment, and the control unit 1 controls each part of the apparatus to measure the optical attenuation characteristics of the photoconductor 2. Except for this point, the operation of the entire apparatus is the same as that of the first embodiment. Therefore, here, with reference to FIG. 12, the description will be made focusing on the “measurement processing of the optical attenuation characteristic” which is a difference from the first embodiment.

FIG. 12 is a flow chart showing a process for measuring the light attenuation characteristic executed in the third embodiment of the image forming apparatus according to the present invention. In this measurement process, first, the exposure energy E is set to the minimum exposure energy Emin (step S111). Then, after forming a solid patch latent image corresponding to the solid patch image on the photoconductor 2 with the exposure energy E (step S112), the surface potential of the solid patch latent image is measured by a surface potential measuring device for measuring the surface potential (step S113). ), Exposure energy E
Are stored in the memory 127 in correspondence with the surface potential.

When the surface potential of the photoreceptor 2 when the light beam L is irradiated on the surface of the photoreceptor 2 is determined by the exposure energy E, it is determined in step S114 whether the exposure energy E exceeds the maximum exposure energy Emax. Judge, "N
O ”, that is, the exposure energy E is the maximum exposure energy E
While the exposure energy E is not more than max, the exposure energy E is incremented by a small amount ΔE in step S115,
Returning to step 112, the above steps S112 and S113 are executed, and the light beam L
The surface potential of the photoreceptor 2 at the time of irradiation with
7 is stored.

Such a series of processing (step S111)
To 115), the photosensitive member 2 indicated by a solid line in FIGS.
Is obtained. After the light attenuation characteristics are obtained in this manner, the optimum exposure energy and the optimum developing bias are obtained in the same manner as in the first and second embodiments.

As described above, according to the third embodiment, the light attenuation characteristics of the photosensitive member 2 can be accurately obtained. In particular, when compared with the first and second embodiments, the following operation and effect can be obtained. That is, the first and second embodiments are based on the premise that the light attenuation characteristics of the photoconductor 2 are known in advance, but even if a plurality of photoconductors are manufactured according to the same standard, there are individual differences, The light attenuation characteristics are not always the same, but rather, the light attenuation characteristics are generally different for each photoconductor 2. In particular, the degree of fatigue / deterioration of the photoreceptor depends on the state of use, which changes the light attenuation characteristics. Although it is possible to store the light attenuation characteristics of the photoconductor in a memory in consideration of this degree, it is not practical because the memory amount is increased. Therefore, as in the present embodiment, the photosensitive member 2
By measuring the light attenuation characteristics of the photoconductor, it is not affected by individual differences of the photoconductor,
The light attenuation characteristics of the photoconductor 2 can be accurately obtained. Therefore, the optimum exposure energy and the optimum developing bias obtained based on the actually measured light attenuation characteristics are more accurate than those obtained in the first and second embodiments, and as a result, the toner image can be formed. It can be formed more stably.

In the third embodiment, a solid patch latent image is formed on the photoreceptor 2 in order to actually measure the light attenuation characteristics. However, the present invention is not limited to the solid patch latent image, and the height is close to the solid patch image. A latent image of a density image, for example, an image in which the area ratio of dots to the entire patch image is about 80% or more may be formed on the photoconductor 2, and the surface potential of the latent image may be measured.

In the third embodiment, the surface potential of the photosensitive member 2 is measured by the surface potential measuring device.
A sensor for measuring the surface potential is previously provided in the image forming apparatus by the photoconductor 2.
May be arranged along the outer peripheral surface of the. In this case, it is more preferable to dispose the sensor around the development position because the surface potential of the photoconductor at the time of development can be measured.

D. Fourth Embodiment In the first embodiment shown in FIG. 3 and the second embodiment shown in FIG. 10, the development γ characteristic is known in advance for each toner color, and the development γ characteristic is determined by an operation unit such as a keyboard (not shown). (Steps S12 and S18), the operator inputs data to the image forming apparatus through the step S12 in FIG.
By executing “processing for measuring the development γ characteristic” shown in FIG. 13 instead of step S18 in FIG.
The characteristics may be measured. The mechanical and electrical configuration of the image forming apparatus according to the fourth embodiment is the same as that of the first embodiment.
The operation of the entire apparatus is the same as that of the first embodiment, except that the development gamma characteristic is actually measured by controlling each part of the apparatus. Therefore, here, with reference to FIG. 13, the description will focus on the “process of measuring the development γ characteristic” which is a difference from the first embodiment.

FIG. 13 is a flowchart showing a process of measuring the development γ characteristic executed in the fourth embodiment of the image forming apparatus according to the present invention. In this measurement process, first, the developing bias Vb is set to the minimum developing bias Vbmin (step S121). Then, after forming a solid patch latent image on the surface of the photoconductor 2 with a predetermined exposure energy E,
The solid patch latent image is developed with toner with the developing bias Vb to form a solid patch image, and the solid patch image is primarily transferred onto the intermediate transfer belt 71 (step S12).
2).

In the next step S123, the developing bias Vb
Is determined to be greater than the maximum developing bias Vbmax, and “NO”, that is, while the developing bias Vb is equal to or less than the maximum developing bias Vbmax, the developing bias Vb is incremented by a small amount ΔVb in step S124, and then, in step S122. Returning to step S122, S123
To form a solid batch image with each developing bias Vb, and transfer the solid patch image to the intermediate transfer belt 71.
Primary transfer.

On the other hand, if "YES" is determined in the step S123, the process proceeds to a step S125, where the patch sensor P
The optical densities of a plurality of solid patch images formed side by side on the intermediate transfer belt 71 are obtained based on the signal output from S, and the optical densities are stored in the memory 127 while corresponding to the developing bias.

Thus, the development γ for a specific toner color
Characteristics are obtained. After the development γ characteristic is obtained in this manner, the optimum exposure energy and the optimum development bias are obtained based on the light attenuation characteristic of the photoreceptor 2 in the same manner as in the first and second embodiments. I have.

As described above, according to the fourth embodiment, the development γ characteristic can be accurately obtained. In particular, when compared with the first and second embodiments, the following operation and effect can be obtained. That is, the first and second embodiments are based on the premise that the development γ characteristics are known in advance, but even if a plurality of developing devices are manufactured to the same standard as in the case of the photoreceptor, the individual differences are still different. The developing gamma characteristics do not always have the same development gamma characteristic, but rather are generally different for each developing unit. In particular,
The degree of fatigue / deterioration of the developing device (the state of the residual toner and the surface condition of the developing device components, particularly the developing roller) depends on the use condition, and the development γ characteristic changes accordingly. Therefore, by actually measuring the development γ characteristic of the photoconductor 2 as in the present embodiment, the development γ characteristic can be accurately obtained without being affected by the individual difference of the developing device and corresponding to the use state. Therefore, the optimum exposure energy and the optimum developing bias obtained based on the actually measured development γ characteristics are higher in accuracy than those obtained in the first and second embodiments, and as a result, the toner image is formed. It can be formed more stably.

In the fourth embodiment, a solid patch image is formed to actually measure the development γ characteristic. However, the present invention is not limited to a solid patch image, and a high-density image close to a solid patch image, for example, An image in which the area ratio of dots to the entire image is about 80% or more may be formed, and the optical density of each high-density image may be measured.

In the fourth embodiment, a plurality of patch images are formed side by side on the intermediate transfer belt 71 functioning as the "image carrier" of the present invention, and the optical density of each patch image is determined by the patch sensor PS. Although the measurement is performed collectively, the optical density of the patch image is measured each time the patch image is primarily transferred to the intermediate transfer belt 71, or the patch image is divided into several blocks, and each block is measured collectively. Alternatively, a density reading sensor different from the patch sensor PS is disposed along the outer peripheral surface of the photosensitive member 2 as a "density measuring means" of the present invention, and a patch formed on the photosensitive member 2 by the sensor is used. The optical density of the image may be measured.

Further, the “development γ characteristic measurement processing” described in detail above can be applied to the third embodiment, and based on the actually measured light attenuation characteristic and development γ characteristic, the high density side and the low density By obtaining the side correlation data, a toner image can be formed more stably.

E. Fifth Embodiment In the first to fourth embodiments, the low-density side correlation data and the high-density side correlation data are obtained based on the light attenuation characteristic of the photoconductor 2 and the development γ characteristic of the developing device. As in the fifth embodiment described below, the low-density side correlation data and the high-density side correlation data may be obtained by so-called patch sensing. Since the mechanical and electrical configuration of the image forming apparatus according to the fifth embodiment is the same as that of the first embodiment, the same reference numerals are given and the description of those configurations is omitted.

FIG. 14 is a flowchart showing a process for optimizing the density control factor in the fifth embodiment of the image forming apparatus according to the present invention. FIG. 15 is a diagram schematically showing a procedure for deriving the optimum exposure energy and the optimum developing bias in the fifth embodiment. In the fifth embodiment, first, correlation data between the exposure energy E and the developing bias Vb for forming a toner image at a high density target density (OD = 1.2) by patch sensing is used as high density correlation data. It is determined (step S21). More specifically, the control unit 1 controls each unit of the apparatus according to the procedure shown in the flowchart shown in FIG. 16 to obtain high-concentration-side correlation data.

FIG. 16 is a flowchart showing a procedure for deriving high-concentration-side correlation data in the fifth embodiment. First, the color for creating a patch image is set to the first color, for example, black (step S211). Then, the charging bias is set to an initial value stored in the memory 127 in advance, and a plurality of patch creation conditions are set (step S212). Here, the exposure energy E is E1, E2,
.., Em and the developing bias Vb is changed to Vb.
(1), Vb (2),..., Vb (n).

While sequentially forming solid patch images (high-density patch images) on the photoreceptor 2 under such patch preparation conditions, each patch image is primarily transferred to the outer peripheral surface of the intermediate transfer belt 71 (step S213). In this embodiment, a solid patch image is formed. However, the present invention is not limited to a solid patch image. For example, a high-density image close to a solid patch image, for example, the area ratio of dots to the entire patch image is about 80% or more. An image may be formed.

In the next step S214, 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 S215). ), Steps S212, S
213 are repeated to form solid patches of other toner colors, that is, cyan (C), magenta (M), and yellow (Y), on the outer peripheral surface of the intermediate transfer belt 71.

On the other hand, if "YES" is determined in the step S214, the optical density of each solid patch image is measured by the patch sensor PS (step S216). In this embodiment, after the solid patch images are formed for all the patch creation colors, the optical densities of the patch images are collectively measured. However, each time a solid patch image for each patch creation color is formed, the solid patch image is formed. Alternatively, the solid patch image may be divided into several blocks, and the optical density of each block may be measured. The same applies to the derivation processing of the low-density-side correlation data described later.

Subsequently, in step S 217, a patch creation condition that matches the high density target density (OD = 1.2) is extracted as “high density correlation data”. For example, FIG.
As shown in FIG. 5A, each patch creation condition (E, Vb)
If the solid patch images created under the patch creation conditions (E1, Vb (2)), (E2, Vb (3)), etc., match the high-density target density,
These (E1, Vb (2)), (E2, Vb (3)),... Become high-concentration-side correlation data.

After obtaining the high-density correlation data in this way (step S21), the exposure energy E and the developing bias for forming a toner image at the low-density target density (OD = 0.2) by patch sensing are obtained. The correlation data with Vb is obtained as low-density-side correlation data (step S2).
2). More specifically, the control unit 1 controls each unit of the apparatus according to the procedure shown in the flowchart shown in FIG. 17 to obtain low-concentration-side correlation data.

FIG. 17 is a flowchart showing a procedure for deriving low-concentration-side correlation data in the fifth embodiment. First, the color for creating a patch image is set to the first color, for example, black (K) (step S221). Then, while setting the charging bias to the initial value, a plurality of patch creation conditions are set (step S222). Here, as in the case of deriving the high density side correlation data, the exposure energy E is changed to E1, E2,..., Em, and the developing bias Vb is changed to Vb (1), Vb (2),. n).

Under such a patch preparation condition, a 1-on-5-off line patch image LI as shown in FIG. 7 is sequentially formed on the photosensitive member 2 as the “low-density patch image (second toner image)” of the present invention. Each patch image is primarily transferred to the outer peripheral surface of the intermediate transfer belt 71 (Step S223).
In this embodiment, 1on5 is used as the low density side image.
Although the off line patch image LI is formed, the present invention is not limited to this line patch image, and various halftone images can be used as patch images. However, when the patch image LI is used as a patch image on the low density side, the following operation and effect can be obtained.

Conventionally, in order to adjust the image density of a line image, for example, in the invention described in Japanese Patent Application Laid-Open No. 9-50155, a patch image formed by outputting a group of three dot lines every three dots is used. The line width is detected by reading the patch image by a sensor. Then, based on the detected line width, the amount of exposure is adjusted by controlling the laser power so that a desired line width is obtained, and an ideal line image is obtained. However, the basic line image is one dot line drawn by one laser beam, and it cannot be said that the line image is sufficiently adjusted only by controlling the line width of a plurality of dot lines as in the conventional example. In contrast, in the present embodiment, FIG.
As shown in (1), a toner image composed of a plurality of one-dot lines spaced apart from each other is formed as a line patch image. Then, as described later, the optical density of the line patch image is measured and adjusted so as to be the low-density side target density, so that the image density of a line image composed of one dot line can be stabilized. .

Also, if the line patch image is 1on5off
Also, advantageous effects can be obtained. The light beam L generally has a Gaussian light intensity distribution, and the design spot diameter is adjusted so that the spot diameter at a level of about 50% of the normal light intensity corresponds to the design resolution. However, in this case, the effective exposure spot diameter corresponding to 1 / e ² effective as the exposure energy is larger than the design spot diameter. Therefore, when the line interval between adjacent one-dot lines is narrow, There is a problem that adjacent effective exposure spots interfere with each other, and the interference changes the surface potential between lines. As a result, the line width of a line originally drawn as a one-dot line becomes thick. On the other hand, such a problem can be solved by providing an interval of 5 lines between adjacent one dot lines as in the present embodiment.
That is, an isolated one-dot line group can be formed without being affected by adjacent lines. Of course, it may be configured to be separated by 6 lines or more.
When the number of ff lines increases, it is necessary to lower the low-density target density accordingly, which may cause a problem in the measurement sensitivity of the patch sensor PS. Therefore, using 1on5off as the line patch image as in the present embodiment can be said to be the most effective patch image when these points are comprehensively considered.

From the viewpoint of increasing the measurement sensitivity of the patch sensor, when raising the low-density target density, a so-called grid pattern of 1 on 5 off in the horizontal direction and 1 on 5 off in the vertical direction is preferable in that it forms an isolated one dot line group. . Also in this lattice pattern, it goes without saying that, in the same manner as described above, six or more lines may be spaced in both the vertical and horizontal directions.

In the next step S224, 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 S225). ), Steps S222, S
By repeating step 223, line patch images of other toner colors, that is, cyan (C), magenta (M), and yellow (Y) are further formed on the outer peripheral surface of the intermediate transfer belt 71.

On the other hand, if "YES" is determined in the step S224, the optical density of each line patch image is measured by the patch sensor PS (step S226).

Subsequently, in step S227, a patch preparation condition that matches the low density target density (OD = 0.2) is extracted as "low density correlation data". For example, FIG.
As shown in FIG. 5 (b), each patch creation condition (E, Vb)
When the line patch images created under the patch creation conditions (E1, Vb (2)), (E2, Vb (3)),... , (E1, Vb (1)), (E2, Vb (3)),... Become low-concentration-side correlation data.

When the high-density side correlation data and the low-density side correlation data are obtained in this way, a product set of both is obtained (step S23). For example, when the high-concentration-side correlation data and the low-concentration-side correlation data are obtained as shown in FIG. 15, the intersection of the high-concentration-side correlation data and the low-concentration-side correlation data is the correlation data (E2, Vb (3)). Becomes Therefore, the exposure energy E2 and the developing bias Vb (3) are set as the optimum exposure energy and the optimum developing bias, respectively, and stored in the memory 127. Here, the correlation data belonging to the intersection is the correlation data (E2, Vb
(3)) has been described as an example, but when there is a plurality of correlation data, one correlation data belonging to the intersection is selected, and the exposure energy and the development constituting the correlation data are selected. The bias may be set as the optimum exposure energy and the optimum developing bias, respectively.

As described above, according to this embodiment, similarly to the first embodiment, the image density of the toner image for each toner color is changed to the low-density target density (OD = 0.2) and the high-density target density (OD = 0.2). OD = 1.2) to stably form an image in a wide density range. In addition, since the density adjustment of the toner image is performed using the exposure energy and the developing bias as density adjusting factors, the exposure energy and the developing energy are simply obtained by calculating the intersection of the low density side correlation data and the high density side correlation data as described above. Bias optimization can be performed. Furthermore, compared to the first to fourth embodiments,
The following operation and effect can be obtained.

First, in the above embodiment, it is necessary to obtain the light attenuation characteristic of the photosensitive member 2 and the development γ characteristic of the developing device in advance, whereas in this embodiment, it is necessary to obtain these characteristics in advance. Therefore, it is possible to more easily optimize the toner image. Another advantage is that the memory does not need to store data according to the state of the apparatus. Further, as described above, the light attenuation characteristic and the development γ characteristic vary depending on the operating condition of the apparatus, the temperature and humidity environment, and the like, and therefore it is desirable to perform the measurement periodically. In particular, in this embodiment, since the exposure energy and the developing bias are optimized by so-called patch sensing, it is possible to flexibly cope with the operation state of the apparatus and the temperature and humidity environment. Examples of the timing of optimizing the exposure energy and the developing bias include a point in time when the apparatus power is turned on and a point in time when the cumulative count value of the number of printed sheets reaches a predetermined value.

In the above-described embodiment, only the data corresponding to the target density is used as the correlation data on the high density side and the low density side. You may make it allow as correlation data. Further, the plurality of correlation data (E1, Vb (2)) obtained in step S21, (E2, Vb
(3)),..., A function of high-concentration-side correlation data, for example, as shown by a one-dot chain line in FIG. 4 is derived, and a plurality of correlation data (E1, Vb ( From 1)), (E2, Vb (3)),..., A function of low-concentration-side correlation data, for example, as shown by a two-dot chain line in FIG. 5, is derived, and an intersection is calculated based on these two functions.
The optimum exposure energy and the optimum developing bias may be set based on the calculation result.

F. Sixth Embodiment In the first to fifth embodiments, the charging bias is fixed, and the image density of the toner image is adjusted by optimizing the exposure energy and the developing bias. The range in which the exposure energy can be changed and set by the unit 123 and the range in which the developing bias can be changed and set by the developing bias generator 126 are finite. Therefore, the optimum exposure energy obtained as described above may be out of the variable range of the exposure energy, or the optimum developing bias obtained as described above may be out of the variable range of the developing bias.
Thus, in the sixth embodiment, the optimum exposure energy and the optimum developing bias are kept within a variable range by changing and setting the charging bias applied from the charging bias generator 121 to the charging unit 3 as described below.

When the charging bias is increased, for example, the light attenuation characteristic of the photosensitive member 2 shifts to the increasing side as shown by broken lines in FIGS. 4 and 5, for example. However, the shift amount changes in accordance with the exposure energy, is relatively large on the low energy side (left hand side in the drawing), decreases with increasing exposure energy, and decreases on the high energy side (right hand side in the drawing). ) Is almost zero. Further, with the fluctuation of the light attenuation characteristic due to the increase of the charging bias, the high density side correlation data changes from the broken line curve to the one-dot chain line curve as shown in FIG. 18, and the low density side correlation data is shown in FIG. Thus, the curve changes from the broken line curve to the two-dot chain line curve. Therefore, the product set of the high density side correlation data and the low density side correlation data shifts from the product set CP0 (E0, Vb0) before the charging bias increase to the product set CP (E, Vb) when the charging bias is increased. Of course, when the charging bias is reduced, the low-density side correlation data, the high-density side correlation data, and the intersection are all shifted in the direction opposite to the direction when the charging bias is increased. As described above, the optimum exposure energy and the optimum developing bias can be changed by changing and setting the charging bias.

Therefore, in the image forming apparatus according to the sixth embodiment, when the optimum exposure energy or the optimum developing bias obtained by the first to fifth embodiments is not within the variable range, the charging bias is changed and set. After that, the exposure energy and the developing bias are optimized by the charging bias. This makes it possible to keep the optimum exposure energy and the optimum developing bias within the variable range. Here, when the charging bias is changed and set, the charging bias may be changed arbitrarily. However, if the state of deviation from the variable range can be confirmed, the charging bias can be set correspondingly. Therefore, in the image forming apparatus according to the sixth embodiment, the charging bias is changed and set after confirming the deviation state. Hereinafter, FIG.
The sixth embodiment will be described in detail with reference to FIG.

FIG. 21 is a flowchart showing a process of optimizing a density control factor in the sixth embodiment of the image forming apparatus according to the present invention. FIG. 22 is a schematic diagram showing the relationship between the intersection and the variable range. Here,
To facilitate understanding of the invention, only the exposure energy can be changed within a predetermined variable range (Emin to Emax), and the developing bias can be changed over a wider range than the optimum developing bias deviation. Suppose that

In the image forming apparatus according to this embodiment,
An intersection is obtained in the same manner as in the first to fifth embodiments. That is, after setting the charging bias to an initial value previously set and stored in the memory 127 (step S31),
The high-density side correlation data and the low-density side correlation data are obtained, and a product set of the correlation data is obtained (step S32), and the exposure energy E and the developing bias Vb belonging to the product set are obtained.

Then, the exposure power control section 123 determines whether or not the exposure energy E obtained in step S32 falls within a variable energy range (Emin to Emax). Similarly to the first to fifth embodiments, the exposure energy E and the developing bias Vb are set as the optimum exposure energy and the optimum developing bias, respectively (step S34).

On the other hand, when it is determined that the exposure energy E obtained in step S32 is out of the variable energy range (Emin to Emax) by the exposure power control unit 123, the process proceeds to step S35 to determine the deviation direction. I do. That is, the exposure energy E is, for example, as shown in FIG.
Whether the current value exceeds the lower limit value Emin of the variable range as shown in (a) and deviates to the low energy side, or exceeds the upper limit value Emax of the variable range and deviates to the higher energy side as shown in FIG. To determine if they are

Specifically, the CPU 12 of the control unit 1
4 obtains the developing biases Vb (h) and Vb (l) corresponding to the lower limit value Emin for each of the high-density side correlation data and the low-density side correlation data. Then, when Vb (h)> Vb (l), it is shifted to the low energy side ((a) in the figure).
When (h) <Vb (l), it is determined that the energy is off to the high energy side (FIG. 9B). The specific discrimination method is not limited to this embodiment. For example, for each of the high-density-side correlation data and the low-density-side correlation data, a developing bias corresponding to the upper limit value Emax is obtained, and the magnitude thereof is determined. The shift direction may be determined based on the comparison.

If it is determined in step S35 that the charge energy has deviated to the low energy side, the flow proceeds to step S36 to reset the charging bias to a high value, and then returns to step S32 to optimize the exposure energy and the developing bias again. On the other hand, if it is determined in step S35 that the charge bias has deviated to the high energy side, the process proceeds to step S37, and the charging bias is reset to a low value.
And the optimization of the exposure energy and the developing bias is executed again.

As described above, according to the sixth embodiment, even when the energy range (Emin to Emax) that can be varied by the exposure power control unit 123 is relatively narrow, the charging bias can be adjusted as needed. By changing and setting, the optimum exposure energy can be kept within the above-mentioned variable range, and the exposure energy and the developing bias can be surely optimized. Moreover, even if the exposure energy obtained in step S32 is out of the variable range, the deviation direction is determined, and the charging bias is increased or decreased in accordance with the deviation direction. In the above-mentioned variable range, and the exposure energy and the developing bias can be optimized efficiently in a short time.

Although the sixth embodiment has been described on the assumption that there is no possibility that the developing bias exceeds the variable range, it is assumed that the developing bias obtained in step S32 exceeds the variable range of the developing bias. Also,
In the same manner as described above, the charging bias may be reset according to the deviation direction.

G. Others The present invention is not limited to the above-described embodiment, and various changes other than those described above can be made without departing from the gist of the present invention. For example, in the above embodiment, the developing bias of the DC component is applied to the developing unit 4. However, for example, as shown in FIG. 23, the developing bias in which the AC component is superimposed on the DC component Vb (DC) is applied. Is also good. When such a developing bias is used, the DC component Vb (DC) may be changed in order to control the developing bias to the optimum developing bias, or the peak between the AC components while the DC component Vb (DC) is fixed. The voltage Vp-p is changed or the high potential period t in one cycle T of the AC component is changed.
The ratio (duty) between h and the low potential period tl may be changed. Further, both the peak-to-peak voltage Vp-p and the ratio (duty) may be controlled while the DC component Vb (DC) is fixed. Alternatively, the frequency of the AC component may be controlled.

In the above embodiment, the optical density OD = 1.2 is used as the high-density target density and the optical density OD = 0.2 is used as the low-density target density. The setting value is not limited to this.

In the above embodiment, the image forming apparatus is capable of forming a color image using four color toners. However, the present invention is not limited to this. Naturally, the present invention can also be applied to an image forming apparatus that forms only the image forming apparatus. 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 sheets such as copy paper, transfer paper, paper, and a transparent sheet for OHP. However, the present invention can be applied to all electrophotographic image forming apparatuses such as copying machines and facsimile machines.

Further, in the above embodiment, the toner image on the photoreceptor 2 is transferred to the intermediate transfer belt 71, the toner image is used as a patch image, the optical density is detected, and the optimum exposure energy is determined based on the detection result. And an optimum developing bias, but the toner image is transferred to an image carrier other than the intermediate transfer belt (transfer drum, transfer belt, transfer sheet, intermediate transfer drum, intermediate transfer sheet, reflective recording sheet or transparent storage sheet, etc.). The present invention can also be applied to an image forming apparatus that forms a patch image by transferring an image.

Further, in the above embodiment, the low-density patches are formed after the high-density patches are formed. However, it is also possible to form a patch in which these patches are mixed and perform sensing.

[0100]

As described above, according to the present invention, low-density correlation data necessary for forming a toner image at a low-density target density and toner images at a high-density target density are formed. Since the product set with the high-density side correlation data required for the product set is obtained, the exposure energy and the developing bias constituting one correlation data belonging to the product set are set as the optimum exposure energy and the optimum developing bias, respectively. The image density of the toner image is controlled to the target density at the two points of high density and low density, and the image density of the toner image can be reliably guaranteed over a wide density range to improve the stability of the image.

Further, in the present invention, the exposure energy and the developing bias are employed as the density adjusting factors for adjusting the image density of the toner image. Does not change, the exposure energy and the developing bias can be optimized by simply calculating the intersection of the low-density side correlation data and the high-density side correlation data as described above. The concentration can be easily stabilized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus of FIG. 1;

FIG. 3 is a flowchart illustrating a process of optimizing a density adjustment factor in the image forming apparatus of FIG. 1;

FIG. 4 is a graph showing a relationship between light attenuation characteristics of a photoconductor and high-density-side correlation data.

FIG. 5 is a graph showing a relationship between light attenuation characteristics of a photoconductor and low-density-side correlation data.

FIG. 6 is a graph showing an example of a development γ characteristic.

FIG. 7 is a diagram schematically showing a line image.

FIG. 8 is a flowchart illustrating a process of deriving low-concentration-side correlation data in the first embodiment.

FIG. 9 is a graph showing a relationship among high-concentration-side correlation data, low-concentration-side correlation data, and a product set.

FIG. 10 is a flowchart illustrating a process of optimizing a concentration control factor according to the second embodiment.

FIG. 11 is a diagram schematically showing the operation of the second embodiment.

FIG. 12 is a flowchart illustrating a process of measuring an optical attenuation characteristic performed in the third embodiment.

FIG. 13 is a flowchart illustrating a measurement process of a development γ characteristic executed in a fourth embodiment.

FIG. 14 is a flowchart illustrating a process of optimizing a concentration control factor in a fifth embodiment.

FIG. 15 is a diagram schematically showing a procedure for deriving an optimum exposure energy and an optimum developing bias in a fifth embodiment.

FIG. 16 is a flowchart illustrating a procedure for deriving high-concentration-side correlation data in the fifth embodiment.

FIG. 17 is a flowchart showing a procedure for deriving low-concentration-side correlation data in the fifth embodiment.

FIG. 18 is a graph showing high-density-side correlation data before and after an increase in charging bias.

FIG. 19 is a graph showing low-density-side correlation data before and after an increase in charging bias.

FIG. 20 is a graph showing the relationship between high-density correlation data, low-density-side correlation data, and intersection before and after the charging bias is increased.

FIG. 21 is a flowchart illustrating a process of optimizing a concentration control factor in a sixth embodiment.

FIG. 22 is a schematic diagram showing a relationship between an intersection and a variable range.

FIG. 23 is a diagram illustrating an example of a developing bias applied to the developing unit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 control unit (control means) 2 photoconductor 3 charging unit (charging means) 4 rotary developing unit (developing means) 4K, 4C, 4M, 4Y developing device (developing means) 6 exposure unit (exposure means) 12) Engine controller (control means) 71 ... Intermediate transfer belt (image carrier) 121 ... Charging bias generation unit 123 ... Exposure power control unit 124 ... CPU (control unit) 126 ... Development bias generation unit 127 ... Memory (storage unit) CP: intersection E: exposure energy L: light beam LI: line patch image (low density patch image) PS: patch sensor (density measuring means) Vb: developing bias

Continued on the front page F-term (reference) 2H003 AA01 BB11 DD03 DD05 DD08 DD11 DD14 2H027 DA02 DA10 DA15 DA50 DE02 DE05 DE07 EA01 EA02 EA05 EC03 EC06 EC19 ED03 ED04 ED09 EE08 2H073 BA01 BA04 BA23 BA28 2H076 DA06 DA07 DA09 DA

Claims (14)

[Claims] An exposure unit configured to form an electrostatic latent image by exposing and scanning a surface of a photoconductor with a light beam; a developing unit configured to visualize the electrostatic latent image with toner to form a toner image; Control means for optimizing an exposure energy of a light beam and a developing bias applied to the developing means to control an image density of a toner image formed by the developing means; Low-density correlation data between the exposure energy for forming a toner image and the developing bias, and the exposure energy and development for forming a toner image with a high-density target density higher than the low-density target density. Optimizes the exposure energy and development bias by setting one correlation data belonging to the product set of the bias and the high-density correlation data as the optimal exposure energy and optimal development bias An image forming apparatus. 2. The low density side correlation data and the high density side correlation data based on a light attenuation characteristic of the photoconductor and a development γ characteristic of the developing means. Image forming device. 3. A storage unit for storing an optimum exposure energy and an optimum developing bias for each film thickness while corresponding to various photoconductor film thicknesses, wherein the control unit stores the film thickness of the photoconductor. Optimization to read out the exposure energy and the developing bias corresponding to the thickness of the photoconductor obtained by the thickness deriving means, and to set the optimum exposure energy and the optimal developing bias, respectively, from the storage means. The image forming apparatus according to claim 2, further comprising: 4. The image forming apparatus according to claim 1, further comprising a surface potential measuring unit configured to measure a surface potential of the photoconductor, wherein the control unit changes and sets the exposure energy of the light beam in multiple steps, and sets the electrostatic latent image at each exposure energy. 4. The image forming apparatus according to claim 2, wherein the surface potential of the electrostatic latent image is obtained by the surface potential measuring means by using the surface potential measuring means, and the light attenuation characteristic of the photoconductor is obtained. 5. 5. An image carrier for supporting a toner image formed on the photoconductor, and a density measuring unit for measuring an image density of the toner image formed on the photoconductor or the image carrier. The control unit forms a toner image as a patch image at each developing bias while changing and setting the developing bias in multiple stages, obtains the image density of the patch image by the density measuring unit, and sets the developing γ characteristic to Claim 2 obtained
5. The image forming apparatus according to any one of claims 1 to 4. 6. An image carrier for carrying a toner image formed on the photoconductor, and a density measuring unit for measuring an image density of the toner image formed on the photoconductor or the image carrier. The control unit forms a first toner image as a high-density patch image in each combination while changing and setting the combination of the exposure energy and the developing bias in multiple stages, and the high-density patch by the density measuring unit. The image density of the image is obtained, and the combination when the image density substantially matches the high-density target density is used as the high-density correlation data, while the combination of the exposure energy and the developing bias is changed and set in multiple stages. Forming a second toner image having a lower density than the first toner image as a low-density patch image in each combination, By seeking the image density of the low-density patch image, the image forming apparatus according to claim 1, wherein the low-density side correlation data combination when the image density is substantially coincident with the low density side target density. 7. The image forming apparatus according to claim 6, wherein in the high-density patch image, an area ratio of dots to the entire patch image is about 80% or more. 8. The image forming apparatus according to claim 6, wherein the low-density patch image is a halftone image. 9. The low-density patch image is composed of a plurality of one-dot lines spaced apart from each other,
9. The image forming apparatus according to claim 8, wherein the plurality of one-dot lines are substantially parallel to each other, and adjacent one-dot lines are separated from each other by an n-line interval (an integer of n ≧ 5). . 10. The image forming apparatus according to claim 1, further comprising a charging unit configured to charge a surface of the photoconductor before forming an electrostatic latent image on the photoconductor, wherein the control unit adjusts an optimal exposure energy from a variable range of the exposure energy. If the deviation or the optimal development bias is out of the variable range of the development bias,
The image forming apparatus according to claim 2, wherein a charging bias applied to the charging unit is changed and the exposure energy and the developing bias are optimized with the charging bias to update the optimum exposure energy and the optimum developing bias. 11. The control unit according to claim 5, wherein when the optimum exposure energy is out of the variable range of the exposure energy or when the optimum developing bias is out of the variable range of the developing bias, the optimum exposure energy exceeds the upper limit of the variable range. The image forming apparatus according to claim 10, wherein it is determined whether the value is out of the range or the value exceeds the lower limit value of the variable range, and the charging bias is changed and set according to a result of the determination. 12. The control means applies a bias in which a DC component and an AC component are superimposed on each other as a developing bias to the developing means, and controls the DC component, the peak-to-peak voltage of the AC component, and one cycle of the AC component. The image forming apparatus according to claim 1, wherein the optimal developing bias is adjusted by controlling at least one of a ratio between a high potential period and a low potential period and a frequency of the AC component. 13. An electrostatic latent image is formed by exposing and scanning a surface of a photoreceptor with a light beam at an optimum exposure energy.
In an image forming method for forming a toner image by visualizing the electrostatic latent image with toner while applying an optimum developing bias to a developing unit, an exposure necessary for forming a toner image at a low density side target density is provided. A first step of obtaining correlation data between energy and a developing bias as low-density-side correlation data; and an exposure energy required to form a toner image at a high-density-side target density higher than the low-density-side target density. A second step of obtaining correlation data between the low density side correlation data and the high density side correlation data as a high density side correlation data; a third step of obtaining a product set of the low density side correlation data and the high density side correlation data; Setting the exposure energy and the developing bias constituting the correlation data of No. 4 as the optimum exposure energy and the optimum developing bias, respectively.
And an image forming method. 14. The optimum exposure energy set in the fourth step is out of the variable range of the exposure energy, or the optimum developing bias set in the fourth step is out of the variable range of the developing bias. Before the formation of an electrostatic latent image on the photoconductor, the charging bias applied to the charging unit for charging the surface of the photoconductor is changed and the first to fourth steps are executed again. 14. The image forming method according to claim 13, wherein the optimal exposure energy and the optimal developing bias are updated by performing the following.