JP2001154425A - Device and method for forming image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the scattering of a line part, a fixing defect and the fluctuation of line width as for an image forming device constituted so that plural image forming units are arranged side by side and almost in parallel and an image forming method. SOLUTION: By a registration detection sensor 6, the toner applying amount and the line width of a line pattern 8 are detected in addition to the writing start position of the images of respective colors. By varying the line toner applying amount or the line width while changing the image forming condition two or more levels, the optimum image forming condition is adjusted based on the optimum image forming condition calculated by a density detection sensor 5 and the measurement data of the line toner applying amount measured by the sensor 6 so that the line toner applying amount becomes a proper value. Besides, the optimum image forming condition is adjusted based on the optimum image forming condition calculated by the sensor 5 and the measurement data of the line width measured by the sensor 6 so that the line width becomes a proper value.

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 method, and more particularly, to an image forming apparatus such as a copying machine or a printer of an electrophotographic type or an electrostatic recording type, and an image forming method using the apparatus.

[0002]

2. Description of the Related Art FIG. 1 is a schematic configuration diagram of a conventional image forming apparatus.
Shown in

This image forming apparatus has a plurality of image forming units substantially parallel to each other in order to speed up multicolor image output.
The multi-color image is formed by sequentially multiple transferring the toner image onto a recording material.

As shown in FIG. 1, this multicolor image forming apparatus includes four image forming units M, C, Y, and M of cyan, yellow, and black as image forming units.
Bk, and further includes a transfer belt 30 and a fixing device 40 as transfer means.

The image forming section of each image forming unit includes photosensitive drums 10M, 10C, 10Y and 10B as image carriers.
k, and around the primary charging rollers 12M, 12C, 1
2Y, 12Bk, laser exposure devices 13M, 13C, 13
Y, 13Bk, and developing units 14M, 14C, 14Y,
14Bk is provided.

The transfer belt 30 includes photosensitive drums 10M and 1M.
0C, 10Y, and 10Bk, and are stretched and driven by a drive roller 31 and a separation roller 32.

The photosensitive drums 11M, 11C, 11Y, 11
Bk is the primary charging rollers 12M, 12C, 12Y, 12
After the surface is uniformly charged to a predetermined potential by Bk,
Exposure is performed by the laser exposure devices 13M, 13C, 13Y, and 13Bk, and an electrostatic latent image corresponding to the document image is formed. The electrostatic latent image formed on the photosensitive drum is developed by developing units 14M, 14C, 14Y, and 14Bk to which a predetermined voltage is applied, and the photosensitive drums 11M, 11C, 11Y, and 1B are developed.
The electrostatic latent image on the 1Bk surface is visualized.

Each of the image forming units M, C, Y, and Bk performs the above-described image forming operation by the electrophotographic process at a predetermined timing, and the photosensitive drums 10M, 10C,
A toner image is formed on 10Y and 10Bk.

The transfer material P fed by the feed roller 20
Is carried on the transfer belt 30 and sequentially conveyed to the transfer portions of the image forming units M, C, Y, and Bk, and the toner images of the respective colors are respectively transferred onto the transfer material P by the transfer rollers 15M, 15C, 15Y, and 15Bk. Is transferred.

The transfer material P after the transfer process is separated from the transfer belt 30 and conveyed to the fixing device 40 where
0, the toner image is fixed by pressing and heating.

As shown in FIG. 2, there is also known an image forming apparatus employing an intermediate transfer member system as a transfer system.

A multicolor image is formed by sequentially transferring the toner images formed by the image forming units M, C, Y, and Bk onto a belt-like intermediate transfer body 80, and a recording material P is formed at a predetermined timing. Feed and transport. The toner image formed on the intermediate transfer member 80 is transferred to the recording material P by applying a voltage of a predetermined polarity by the transfer device 100. The toner image formed on the recording material P is fixed by the fixing device 40.

After the transfer step to the transfer material P is completed, the toner remaining on the intermediate transfer member (so-called transfer residual toner) is scraped by an intermediate transfer member cleaning unit 33 comprising a fur brush, a rubber blade, or a combination thereof. It is taken, collected, and proceeds to the next image forming step.

In the multicolor image forming apparatus, density control for stabilizing the toner density of each color is performed. By performing this density control, delicate color reproduction, scattering prevention by suppressing the amount of applied toner, and the like can be achieved.

The density detection sensor 5 shown in FIGS. 1 and 2 will be described with reference to FIG.

In FIG. 3, the density detecting sensor 5 is arranged near the center of the separation roller 32 in the longitudinal direction, facing the transfer belt 30 with a predetermined gap. The density detection sensor 5 detects the density of the patch pattern of the transferred image formed and carried on the transfer belt 30. Then, the image forming conditions are adjusted according to the detected density to realize the optimum image density.

A writing position detection sensor 6 (hereinafter, referred to as a “registration detection sensor 6”) for adjusting the writing position of each color is substantially the same as the density detection sensor 5, facing the transfer belt 30. They are arranged with a predetermined gap. One registration detection sensor 6 is provided near each end of the separation roller 32. The writing start position of a line or the like having a predetermined width formed on the transfer belt 30 at a predetermined timing for each color is detected by the registration detection sensor 6. The difference between the write timing of each color between the actually measured value and the theoretical value is fed back to the write timing at the time of image formation and corrected to try to form an image without color shift.

[0018]

However, the first object of the density control by the density detection sensor as in the above-mentioned conventional example is to stabilize the maximum image density. But,
Generally, the line density tends to be higher than the maximum density (that is, the solid density). This is because the amount of applied line toner tends to be larger than the amount of solid toner applied under the same image forming conditions (latent image / development conditions). Therefore, even if the solid density is satisfied, the line density increases. That is, since the amount of applied line toner increases, there is a problem that the following image quality degradation occurs.

(1) Line portion scattering Since the amount of applied line toner is large, when the toner is transferred onto the transfer material, the excessive amount of toner is scattered without being sufficiently transferred. Looks blurry.

(2) Insufficient Fixing Since the amount of applied line toner is too large, a sufficient amount of heat cannot be applied to the toner and the transfer material at the time of final fixing. Would.

(3) Line Width Fluctuation The line width sometimes greatly fluctuates from the target value due to the fluctuation of the line toner amount. The line width is an important setting value for determining the image quality of characters and the like, and it is impossible to realize high-definition character reproducibility due to line width fluctuation.

Therefore, the present invention has been made in view of the above problems, and in a multicolor image forming apparatus in which a plurality of image forming units are arranged substantially in parallel, an image forming apparatus capable of solving the above problems is provided. And an image forming method using the apparatus.

[0023]

According to a first aspect of the present invention, there is provided a visual image obtained by forming a latent image by exposure means and developing the latent image under predetermined image forming conditions. Means for carrying visible images of different colors,
A plurality of image carrying means disposed substantially in parallel with each other, and the visible images by the plurality of image carrying means are arranged opposite to the plurality of image carrying means, and carry the transferred visible image. A transfer unit that conveys in the direction in which the plurality of image carriers are provided; and a transfer unit that is provided to face a predetermined position near an end of the transfer unit along the direction in which the transfer unit is provided. An image forming apparatus comprising: a first optical detection unit for detecting a density; and a second optical detection unit for detecting an image density at a position different from the facing position on the transfer unit. A first control unit for forming a detection patch and controlling to form an image writing position detection pattern, and a control for detecting the formed patch and pattern by the first and second detection units. Second control means; Wherein by changing the image forming condition in accordance with information obtained by the detection to measure the patch by the first optical detection means, third to optimally control the image density on the transfer means in accordance with the measured value
An image forming apparatus comprising a control unit.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the image density detection patches are a plurality of line images arranged in the direction in which the patches are arranged. The image forming condition is controlled so that the line image is appropriate based on the optimum image forming condition calculated by detecting the plurality of line images by a detecting unit and the measurement value by the first optical detecting unit. An image forming apparatus is provided.

According to a third aspect of the present invention, there is provided the image forming apparatus according to the second aspect, wherein the amount of the developer in the line image is optimally controlled.

According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the second aspect, wherein the width of the line image in the direction in which the line images are arranged is optimally controlled. .

According to a fifth aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the transfer means is in the form of an endless belt.

According to a sixth aspect of the present invention, in the image forming apparatus of the first aspect, the first optical detecting means calculates a first image forming condition for forming a target image density.
An image forming apparatus is provided, wherein the second optical detecting means calculates a second image forming condition for forming a target amount of developer or a target linear image density.

According to a seventh aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming condition is such that a charging voltage value for charging the surface of the image carrying means or the image carrying means is provided with the charging voltage value. An image forming apparatus including a developing bias voltage for applying a developer is provided.

The invention of claim 8 is a means for carrying a visible image obtained by performing formation of a latent image by the exposure means and development of the latent image under predetermined image forming conditions. A plurality of image carrying means for carrying an image and arranged substantially in parallel with each other; and the visible images transferred by the plurality of image carrying means arranged in opposition to the plurality of image carrying means and the transferred visual image A transfer unit for carrying the plurality of image carriers in the direction in which the plurality of image carriers are disposed, and disposed opposite to a predetermined position near an end of the transfer unit along the direction in which the transfer unit is disposed; First optical detection means for detecting the image density at the opposed position;
An image forming method for an image forming apparatus, comprising: a second optical detection unit that detects an image density at a position different from the opposing position on the transfer unit, wherein an image density detection patch is formed on the transfer unit. A first step of controlling to form an image writing position detection pattern, a second step of controlling the formed patch and pattern to be detected by the first and second detection means, Changing the image forming conditions according to the obtained information to measure the patch by the first optical detection means, and optimally controlling the image density on the transfer means according to the measured value. An image forming method is provided.

According to a ninth aspect of the present invention, in the image forming method according to the eighth aspect, a plurality of line images arranged in the arrangement direction are used as the image density detection patches, and The image forming condition is controlled so that the line image is appropriate based on the optimum image forming condition calculated by detecting the plurality of line images by a detecting unit and the measurement value by the first optical detecting unit. To provide an image forming method.

In the image forming apparatus and the image forming method using the apparatus according to the present invention having the above-described configuration, the first optical detection means detects a write start position of each color and a predetermined line pattern (line image). Toner (developer) loading amount
It has a function of detecting the line width, and changes the applied amount of line toner or the line width while changing the image forming condition by at least two steps, thereby obtaining the optimum image forming condition calculated by the second optical detecting means and the first optical detecting condition. From the measurement data of the applied amount of line toner measured by the means, the optimum image forming condition is adjusted so that the applied amount of line toner becomes an appropriate value. Further, the optimum image forming condition is adjusted based on the optimum image forming condition calculated by the second optical detecting means and the line width measurement data measured by the first optical detecting means so that the line width becomes an appropriate value. By these adjustments, it is possible to avoid image quality defects caused by a large line toner density, a large amount of applied line toner, a fluctuation in line width, and the like.

[0033]

(First Embodiment) FIG. 1 is a side view showing a schematic configuration of an image forming apparatus capable of implementing a first embodiment according to the present invention. Note that the image forming apparatus having the configuration shown in FIG. 2 can also implement the first embodiment according to the present invention.

The image forming apparatus of this embodiment is a multicolor image forming apparatus in which four image forming units are arranged in parallel on a transfer belt, and each image forming unit has a resolution of 6
00 dpi (dot per inch). That is, the diameter of one dot is about 42 μm.

Referring to FIG. 1, this image forming apparatus has a plurality of image forming units M, C, Y, and Bk, and a transfer belt 30 serving as a transfer material conveying means is arranged vertically through each image forming unit. Has been established. Each image forming unit M, C, Y, Bk has a cylindrical photosensitive drum 11M, 11C, 11Y, 11Bk as an image carrier.
Are rotatably supported in the direction of arrow a. Each photosensitive drum is coated with a photosensitive member.

Reference numerals 12M, 12C, 12Y, and 12Bk denote primary chargers for the photosensitive drums.
1C, 11Y, and 11Bk are arranged at predetermined intervals. Laser exposure devices 13M, 13C, 13Y, 13B
k is the primary charger 12M, 12C, 12Y, 1
For 2Bk, the photosensitive drums 11M, 11C, 11Y, 1
Each photoconductor is exposed on the downstream side in the rotation direction of 1 Bk.
The developing units 14M, 14C, 14Y, and 14Bk store magenta, cyan, yellow, and black toners, respectively, and further downstream of the laser exposure device arrangement positions of the photosensitive drums 11M, 11C, 11Y, and 11Bk. They are located adjacent to each other.

The transfer belt 30 stretched by the driving roller 31 and the separation roller 32 carries and conveys the transfer material P supplied from the paper supply unit 20, and the photosensitive drums 11M, 11C, 11
Y and 11Bk are driven in the direction of arrow b.

Transfer chargers 15M, 15C, 15Y, 15
Bk is arranged at the transfer position of each color image so as to sandwich the transfer belt 30 in cooperation with each photosensitive drum in order from the upstream side in the moving direction of the transfer belt 30. The transfer belt cleaning unit 33 has a mechanism (not shown) for contacting and separating the transfer belt 30 and can clean the transfer belt 30.

An image forming operation of the image forming apparatus having the above-described configuration will be described by taking the image forming unit M for magenta image as an example. The image forming units of other colors perform the same image forming operation.

The photosensitive drum 11M as an image carrier is an organic photosensitive drum having an outer diameter of Φ30 (mm).

Dark potential -600 (V), bright potential -20
After the surface of the photosensitive drum 11M is uniformly negatively charged by the primary charger 12M so as to be 0 (V), the electrostatic latent image corresponding to the original image is exposed by performing exposure by the laser exposure device 13M. It is formed on the drum 11M.

The developing device 14M uses a non-magnetic one-component jumping developing method, and a DC voltage (-300 to -500 (V)) and an AC voltage (2 kVpp, 2 kHz) are applied to the developing carrier at a predetermined timing. The electrostatic latent image is superimposed and developed with toner to develop the electrostatic latent image on the photosensitive drum 11M into a visible image (visible image).

The toner image formed on the surface of the photosensitive drum 11M has a positive DC bias 71M at a predetermined timing.
By the transfer roller 15M to which (+100 to +1500 (V)) is applied, the image is transferred onto the transfer material P supplied from the sheet feeding unit 20 to the transfer belt 30 in synchronization.

On the other hand, the toner remaining on the surface of the photosensitive drum 11M after the transfer is cleaned by the cleaning unit 33, and proceeds to the next image forming step.

The above operation is performed in each of the image forming units M, C, Y, and Bk at a predetermined timing, and each color toner image formed on the photosensitive drums 11M, 11C, 11Y, and 11Bk is held on the transfer belt 30. Are sequentially transferred to the transfer material P. The transfer material P to which the respective color toner images have been transferred is supplied to the fixing device 40 by the transfer belt 30, where the image is fixed by heating and pressing operations, and a full-color image is obtained.

The surface of the transfer belt 30 that has finished supplying the transfer material P to the fixing device 40 is cleaned by a belt cleaner 33.

Next, the density control performed in the multicolor image forming apparatus according to the present invention will be described.

FIG. 3 is a perspective view showing the positional relationship between the density detection sensor and the registration detection sensor with respect to the transfer belt.

The density detecting sensor 5 disposed near the center of the separation roller 32 in the longitudinal direction (the center in the width direction of the transfer belt 30) is of an optical type, and is 3.0 (m) away from the transfer belt 30.
The transfer belt 30 is disposed to face the transfer belt 30 with a gap of m).
The density detection sensor 5 has a light source, and has a peak sensitivity wavelength of 960 (nm) with respect to the patch formed on the transfer belt 30.
The light is emitted and emitted with a constant light amount, and the light amount reflected from the patch is received and detected by a photodiode.

Normally, the amount of reflected light changes in correlation with the amount of toner (density). Therefore, the patch density can be detected by converting the amount of light received by the photodiode into a density. More specifically, the amount of reflected light has a correlation with the amount of toner in the irradiated portion of the density detection sensor. However, this irradiation portion toner amount, development,
Since an approximately one-to-one relationship is established between the optical toner densities on the transferred transfer material, the magnitude of the reflected light amount has a correlation with the amount of the toner or the level of the toner density. Here, the toner amount indicates a toner mass per unit area, and is a physical amount expressed in units (mg / cm ² ).

Next, registration detection control (hereinafter referred to as "registration detection control") will be described.

The registration detecting sensor 6 has the same optical mechanism and characteristics as those of the density detecting sensor 5. The registration detecting sensor 6 is disposed facing the transfer belt 30 with substantially the same predetermined gap as the density detecting sensor 5. The registration detection sensors 6 are provided one by one at predetermined positions near both ends of the separation roller 32 and inside from both ends of the transfer belt 30.

Line patterns 8 of each color are formed at predetermined intervals on the transfer belt 30 at positions corresponding to the positions of the registration detection sensors 6 at predetermined intervals. The formed line pattern 8 is detected based on the same principle as that of the density detection sensor 5, thereby calculating the writing start timing of each color. The formation of the line pattern 8 will be described later in detail with reference to FIG.

The difference between the actually measured value and the theoretical value of the subsequent cyan, yellow, and black writing positions is corrected based on the writing position of magenta, which is the first color, and the laser exposure devices 13M, 13C are corrected based on the corrected values. , 13Y, 1
By correcting the exposure timing by 3Bk, optimal image formation without color shift is achieved.

The above-mentioned two optical sensors (density detection sensor 5 and registration detection sensor 6) have different spot diameters at the irradiation positions in order to secure their respective optimum output characteristics.
The spot diameter of the density detection sensor 5 is about 6 (mm), and the density detection sensor 5 is suitable for measuring the density of a patch pattern having a size of about 20 × 20 (mm). The spot diameter of the registration detection sensor 6 is about 0.4 (mm), and the registration detection sensor 6 is suitable for measuring the line density of a line pattern of several dots to about 10 dots.

Next, the control according to the present invention will be described with reference to the measurement diagram of FIG. 4 and the flowchart of FIG.

The density control is performed for each color, and the developing device 14 is controlled so that the image forming condition changes from the low density side to the high density side.
M, 14C, 14Y, 14Bk developing bias (horizontal axis)
From -300 (V) to -500 (V) to -50 (V)
While sequentially changing at intervals, five density detection patches of each color are formed (step S11 in FIG. 5). Then, the patch density (vertical axis) is detected (S12), and the relationship between the patch density and each developing bias is measured. The relationship obtained here is compared with the target density TD, and a density developing bias DB for realizing the target density TD is calculated (S13).

As the density detecting pattern (patch pattern), a 60% halftone pattern was employed for the purpose of further stabilizing the density gradation characteristics.

In the registration detection control, a horizontal line pattern having a width of 10 dots was adopted as the line pattern 8. By employing this pattern, the measurement of the image writing position and the measurement of the amount of applied line toner can be simultaneously achieved.

In general, the amount of applied toner of a line pattern tends to gradually increase as the line width increases with respect to the amount of applied toner of a solid image.
In many cases, the amount of applied toner of a line pattern having a dot width shows a peak.

FIG. 6 is a measurement diagram showing actually measured values according to a pattern output by the image forming apparatus according to the present invention.

FIG. 6 shows that the amount of applied toner of the solid image is 0.
The relationship between the line width of various line patterns and the amount of applied toner under a constant image forming condition (constant developing bias) of 60 mg / cm ² is shown. As can be seen from this relationship, in the case of a 10 dot line pattern or a 20 dot line pattern, the applied toner amount is 0.74 mg / c.
The maximum value is about m ² , and it can be confirmed that the amount of applied toner varies depending on the line width.

Therefore, it can be understood that by measuring the 10-dot line pattern, it is possible to perform the measurement under the strictest condition of the applied amount of line toner, that is, the condition that gives the maximum applied amount of line toner.

The purpose of the registration detection control is to detect the writing start position between each color. At the same time, in order to measure the amount of toner applied to the line pattern, the same procedure as that for the density control is performed, and the development bias is set to 5 levels for each color. A book line pattern is formed (Step S16 in FIG. 5).

FIG. 7 is an explanatory diagram for schematically explaining line width detection. Since the line width detection is performed by the same method as the density control, FIG. 7 shows a state in which the line width increases as the image forming condition (developing bias) changes (bias increase).

Since the registration detecting sensor 6 is arranged at a position 30 mm from the end of the transfer belt 30, a predetermined line from the end of the transfer belt 30 is formed as a line pattern 8 so that the center can be measured by the sensor. Distance (20
mm), 10-dot line patterns having a length of 20 mm are formed at predetermined intervals. Although the line pattern formation position in the transfer belt transport direction is originally the same as the density control patch formation position, FIG. 7 shows a slightly narrowed line interval for easy understanding.

In the present embodiment, the line width with respect to the developing bias formed by the above-described procedure is measured, and the optimum line developing bias LB which becomes the target amount of applied line toner is measured by the same method as that described with reference to FIG. Is calculated (steps S17 and S18 in FIG. 5).

The optimum density developing bias DB (Density Bias) obtained by the density control and the optimum line developing bias LB obtained by the line control
(Line Bias) for comparison (S2
0), the developing bias is controlled based on the following relationship.

1) In the case of DB ≦ LB Under these conditions, the image forming conditions (DB) satisfying the density
In this case, the amount of applied toner on the line does not reach the condition that causes scattering or poor fixing. That is, since it means that no image defect occurs, the optimum developing bias is set to DB (S22).

2) Case of DB> LB Under these conditions, image forming conditions (DB) satisfying the density
In this case, there is a very high possibility that scattering due to the line portion and defective fixing occur. That is, it means that it is difficult to guarantee the image quality, so the optimum developing bias is set to LB (S24).

Under the above conditions, the target control density of the density control is set to 1.00 (optical density value), and the target control applied amount of the line control (calculated from the correlation between the line applied amount and the optical density) is set to 0.80.
mg / cm ² (Maximum amount of applied toner 1.
60 mg / cm ² was set as a limit value of scattering and fixing failure), and the effect of the above control was confirmed.

The above control is continuously performed under a normal environment.
Continued checking the output image quality. It should be noted that the effect was confirmed by checking each of the first color magenta and the second color cyan by 1 respectively.
200 (%) of the secondary color (blue) on each of 00 (%)
This was performed using a line.

The image forming units M, C, Y, and Bk have stable developability and the like in the initial stage of the operation.
The calculated optimum developing bias was always DB for both magenta and cyan, and there was no problem. However, as the measurement was continued and the frequency of use of the developing units 14M, 14C, 14Y, and 14Bk increased, the amount of toner applied to the line pattern 8 increased. For this reason, in the latter half of the life of the developing device, the frequency at which LB is calculated as the optimum developing bias for both magenta, cyan, and sometimes both has increased. However, high-quality images can be stably obtained without causing image defects such as line scattering. The output of the image could be maintained.

The same evaluation as described above under a normal environment was performed under a high-temperature and high-humidity environment, which is severely conditioned against line scattering, and under a low-temperature, low-humidity environment, which is strictly required against fixing failure. It has been confirmed that the line control according to the present invention works properly under any of the environments, and the effect of preventing the occurrence of scattering and fixing defects can be suppressed.

Further, by implementing the line control method described in the present embodiment, it is possible to perform density control and line control independently and simultaneously, and it is possible to avoid an increase in control time.

As described above, according to the present embodiment,
By providing the registration detection sensor 6 with an image writing position detection function and a line toner application amount detection function, it is possible to satisfy the image density and suppress the line toner application amount without extending the control time of the density control. ,
As a result, a conventional image defect problem such as scattering or defective fixing can be solved.

(Second Embodiment) In this embodiment, at the same time as the density control by the density detection sensor, the registration detection sensor measures the line width of the line pattern for writing start position detection, and feeds the measurement result back to the image forming condition. Control. The purpose of the control of the present embodiment is that the line width is a parameter that is indispensable for reproducing sharp edges such as line drawing of characters and graphics, and that the line width is controlled to stabilize the edge reproduction. By doing so, tight image quality is realized.

Note that the basic configuration of the image forming apparatus capable of implementing this embodiment and the conditions of density control are the same as those described in the first embodiment.

In the line control according to this embodiment, the line width of the 10-dot line pattern is measured by the registration detection sensor 6, and the above-described feedback control is performed.

The principle of measuring the line width will be described.

When the irradiation light spot of the registration detecting sensor 6 reaches the line pattern portion on the transfer belt 30, the reflection of the line portion by the toner starts, and the light receiving sensor (photodiode) approaches the center of the line portion. Output gradually increases. Then, the output of the light receiving sensor gradually decreases as the irradiation light spot moves away from the center of the line portion.

The time t from the time when the output of the light receiving sensor starts rising to the time when the output of the light receiving sensor returns to the base output is measured, and the time t is multiplied by the transport speed Vb of the transfer belt 30 to obtain the following equation. The line width Lw is calculated.

[0083]

Lw = t * Vb In general, the image density (solid density) is, as shown in FIG. 8, the development contrast potential (development bias potential and photoconductor surface exposure) indicated by solid lines 80, 81, and 82 with double arrows. (Potential difference from the partial potential). On the other hand, the line width is equal to the back contrast potential (the potential difference between the non-exposed portion potential (dark portion potential VD) on the photosensitive drum surface and the developing bias potential) indicated by broken lines 83, 84, and 85 with double arrows as shown in FIG. Depends and changes.

Therefore, the image density is stable at a constant development contrast potential, and under this condition, the image density is not affected by the change in the back contrast potential. That is, it is possible to adjust the line width while satisfying the image density at a constant development contrast potential.

Therefore, in this embodiment, line width control is performed according to the control flow shown in FIG.

The same procedure as in the first embodiment (step S10)
The density developing bias DB that realizes the target density TD is calculated by (1, S102, S103). Further, the amount of applied toner on each line is detected by the same procedure (steps S106 and S107) as in the first embodiment, and the calculated bias D
A line width LW (Line Width) for B is calculated (step S110).

Next, in and after step S112, the calculated LW, TL (line width lower limit allowable value), TM (line width target center value), and TH, which are the control target values of the line width, respectively.
The relationship of (line width upper limit allowable value) is determined, and the process proceeds according to the determination result. That is, if the line width LW is within the allowable range with respect to the control target value, step S1
20, the developing bias is set to the optimum developing bias and the reference charging bias PCB (Primary Charge).
r Bias) is determined as the optimal charging bias.

If the line width LW is out of the permissible range, the process proceeds to step S114 and thereafter, and the line width is adjusted by further applying the primary charging bias. On the basis of the result, an optimum primary charging bias is calculated by comparing with the control target, and the calculated value is determined as the optimum primary charging bias.

The above processing will be further described below. FIG. 10 is a schematic diagram of calculating the optimum value under each condition.
11 to FIG.

1) In the case of TL ≦ LW ≦ TH DB is set as the optimum developing bias and the ordinary primary charging bias PCB is set as the optimum primary charging bias (step S1).
20). This is because it can be determined that the detected line widths in the developing bias DB and the primary charging bias PCB satisfy the image quality as shown in FIG.

2) In the case of LW <TL (FIG. 11) Since the line width is small in the DB, the line width adjustment control is executed according to the following flow.

The line width adjustment control has almost the same image forming conditions as the registration detection control, but a five-stage (five) 10-dot line pattern is formed under the following conditions (step S13).
0, S140).

The developing bias for forming the five-stage line is fixed at DB. The primary charging bias forming the first line is set to the initial set value PCB1. Thereafter, the second to fifth lines are separated from the PCB 1 by a predetermined interval (25
In (V)), the primary charging bias is reduced, and the line width is gradually increased. That is, a line pattern is formed by changing the charging bias according to the following equation.

[0094]

## EQU2 ## PCBn = PCB1-25 * (n-1) where n = 1 to an integer of 5 Each line width formed under the above conditions is detected (step S1).
31), the primary charging bias PCBL which is the line width target center value TM is calculated from the relationship between the primary charging bias and the line width (step S132), and the value is used as the optimum image forming condition (step S133).

3) In the case of TH ≦ LW (FIG. 12) Since the line width is large in the DB, the line width adjustment control is executed according to the following flow.

The line width adjustment control has almost the same image forming conditions as the registration detection control, but a five-stage (five) 10-dot line pattern is formed under the following conditions (step S13).
0, S140).

The developing bias for forming the five-stage line is fixed at DB. The primary charging bias forming the first line is set to the initial set value PCB1. Thereafter, the second to fifth lines are separated from the PCB 1 by a predetermined interval (25
(V)), the primary charging bias is increased, and the line width is gradually reduced. That is, a line pattern is formed by changing the charging bias according to the following equation.

[0098]

## EQU3 ## PCBn = PCB1 + 25 * (n-1) where n is an integer of 1 to 5 Each line width formed under the above conditions is detected (step S1).
41), a primary charging bias PCBH serving as a line width target center value LM is calculated from the relationship between the primary charging bias and the line width (step S142), and the value is set as an optimum image forming condition (step S143).

Under the above conditions, the target control density of the density control was set to 1.00 (optical density value), and the line width control target value of the line width control was set to 480 (μm).

The above control is continuously performed under a normal environment.
Continued checking the output image quality. In confirming the effect, evaluation was made mainly on scattering of monocolor lines or characters.

Since the image forming units M, C, Y, and Bk have stable developing properties at the beginning of operation,
With the calculated optimum developing bias, the line width was always within a substantially desired range (between TL and TH), and there were no problems such as overall image quality, line dispersion, blur, and the like.
However, the measurement is continued and the developing units 14M, 14C, 1
As the frequency of use of 4Y and 14Bk increases, the line width of the line pattern 8 gradually increases. For this,
In the latter half of the life of the developing unit, although the line width control is frequently executed, the line width becomes extremely large due to the optimal primary charging bias, and the image quality is significantly impaired. The output of a high-quality image could be stably maintained without any problem.

For comparison, when the line width control was executed, the image formation was performed with the primary charging bias set to a normal value while the optimum developing bias was fixed.
The dot line pattern width is about 550 (μm),
Character scattering was remarkable, blurring such as a line pattern was observed, and the image quality was unacceptable.

The same evaluation as described above under a normal environment was performed in the early morning under a high-temperature and high-humidity environment where the line generally became thick, and in the early morning under a low-temperature and low-humidity environment where the line became thin. It was confirmed that the line width control according to the present invention was properly executed in each environment, and the optimum line width could be reproduced while satisfying the entire image density.

As described above, according to the present embodiment,
By providing the registration detection sensor 6 with an image writing position detection function and a line toner application amount detection function, the image density can be satisfied and the line width can be within the allowable range. The conventional image defect problems, such as scattering of characters and blurring, can be solved.

[0105]

As described above, according to the present invention, an image forming apparatus in which a transfer belt or an intermediate transfer belt is used as transfer means and a plurality of image bearing means for different colors are arranged in parallel with the transfer means. In addition to performing the density control for stabilizing the overall density of the image, the registration detection sensor (first optical detection means) performs the registration detection control, and also measures the amount of applied line toner or the line width. By adjusting the image forming conditions (primary charging bias and developing bias) to the optimum values by carrying out, it is possible to reduce the amount of the developer applied to the line image or to adjust the line width of the line image to the optimum value. Line scattering, character scattering,
There is an effect that it is possible to prevent image quality deterioration such as poor fixing or thick or thin line width.

[Brief description of the drawings]

FIG. 1 is a side view showing a schematic configuration of an image forming apparatus capable of implementing first and second embodiments according to the present invention.

FIG. 2 is a side view illustrating another schematic configuration of an image forming apparatus capable of implementing the first and second embodiments according to the invention.

FIG. 3 is a perspective view showing an arrangement of an optical sensor according to the first and second embodiments.

FIG. 4 is a measurement diagram showing an outline of density control in the first embodiment.

FIG. 5 is a flowchart illustrating control according to the first embodiment.

FIG. 6 is a measurement diagram schematically illustrating the amount of applied toner in the first embodiment.

FIG. 7 is an explanatory diagram for explaining the outline of line load amount detection in the first embodiment.

FIG. 8 is a characteristic diagram schematically showing a line width and a potential setting in the second embodiment.

FIG. 9 is a flowchart illustrating control according to the second embodiment.

FIG. 10 is an explanatory diagram specifically explaining a control flow process in the second embodiment.

FIG. 11 is an explanatory diagram specifically explaining another process of the control flow in the second embodiment.

FIG. 12 is an explanatory diagram specifically explaining still another process of the control flow in the second embodiment.

[Explanation of symbols]

 5 Density detection sensor 6 Registration detection sensor 8 Line pattern 11M, 11C, 11Y, 11Bk Photosensitive drum 12M, 12C, 12Y, 12Bk Primary charging roller 13M, 13C, 13Y, 13Bk Laser exposure device 14M, 14C, 14Y, 14Bk Developing device 30 Transfer belt 33 Intermediate transfer member cleaning unit 40 Fixing device M, C, Y, Bk Image forming unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/16 G03G 21/00 372 21/14 F-term (Reference) 2H027 DA09 DA21 DE07 DE10 EA01 EA05 EC03 EC06 EC07 ED04 ED06 ED24 EE02 FA28 2H030 AA01 AB02 AD12 AD17 BB16 BB23 BB34 BB36 BB42 BB44 BB56 BB63 2H032 AA05 BA09 BA18 CA13 CA15 2H076 AB02 AB66 DA42

Claims (9)

[Claims] 1. A means for carrying a latent image obtained by performing formation of a latent image by an exposure means and development of the latent image under predetermined image forming conditions, carrying visible images of different colors, and A plurality of image carrying means arranged in parallel, and the visible images by the plurality of image carrying means are disposed opposite to the plurality of image carrying means, and the plurality of image carrying means carry the transferred visual images. A transfer unit that conveys the image carrier in a direction in which the image carrier is disposed; and a transfer unit that is disposed to face a predetermined position near an end of the transfer unit along the direction in which the image carrier is provided, and that the image density at the facing position An image forming apparatus comprising: a first optical detection unit for detecting; and a second optical detection unit for detecting an image density at a position different from the opposing position on the transfer unit. A patch is formed, and a pattern for detecting an image writing position is formed. First control means for controlling to form a patch, second control means for controlling the formed patch and pattern to be detected by the first and second detection means, and information obtained by the detection. And a third control unit that optimally controls the image density on the transfer unit according to the measured value by measuring the patch by changing the image forming condition according to the first optical detection unit. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein the image density detection patches are a plurality of line images arranged in the direction in which the patches are arranged, and the plurality of lines are arranged by the second optical detection unit. An image forming apparatus, comprising: controlling an image forming condition based on an optimum image forming condition calculated by detecting an image and a value measured by the first optical detection unit so that the line image is appropriate. 3. The image forming apparatus according to claim 2, wherein the amount of the developer in the line image is optimally controlled. 4. The image forming apparatus according to claim 2, wherein the width of the line image in the direction in which the line images are arranged is optimally controlled. 5. The image forming apparatus according to claim 1, wherein the transfer unit has an endless belt shape. 6. The image forming apparatus according to claim 1, wherein said first optical detecting means calculates a first image forming condition for forming a target image density, and said second optical detecting means calculates a target developer amount. Alternatively, an image forming apparatus for calculating a second image forming condition for forming a target line image density. 7. The image forming apparatus according to claim 1, wherein the image forming condition is a charging voltage value for charging a surface of the image bearing unit or a condition for applying the developer to the image bearing unit. An image forming apparatus comprising a developing bias voltage. 8. A means for carrying a visible image obtained by performing formation of a latent image by the exposure means and development of the latent image under predetermined image forming conditions, carrying visible images of different colors, and A plurality of image carrying means arranged in parallel, and the visible images by the plurality of image carrying means are disposed opposite to the plurality of image carrying means, and the plurality of image carrying means carry the transferred visual images. A transfer unit that conveys the image carrier in a direction in which the image carrier is disposed; and a transfer unit that is disposed to face a predetermined position near an end of the transfer unit along the direction in which the image carrier is provided, and that the image density at the facing position An image forming method for an image forming apparatus, comprising: first optical detecting means for detecting; and second optical detecting means for detecting an image density at a position different from the facing position on the transfer means. Form image density detection patches and write images A first step of controlling so as to form a position detection pattern; a second step of controlling the formed patches and patterns to be detected by the first and second detecting means; A third step of measuring the patch by the first optical detection unit while changing the image forming condition according to information, and optimally controlling the image density on the transfer unit according to the measured value. An image forming method comprising: 9. The image forming method according to claim 8, wherein a plurality of line images arranged in the arrangement direction are used as the image density detection patches, and the plurality of lines are detected by the second optical detection unit. An image forming method, comprising: controlling an image forming condition based on an optimum image forming condition calculated by detecting an image and a value measured by the first optical detection unit so that the line image is appropriate.