JP2005017627A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively provide an image forming apparatus capable of stably outputting a high-quality toner image while maintaining productivity without being influenced by the characteristic (whether it is a high-density image or a low-density image or the like) of the outputted image. <P>SOLUTION: The image forming apparatus has an image forming means including a developing means and forming the toner image on a carrier, a density measuring means measuring the density of the toner image, a density control means performing density control operation that toner amount supplied to the developing means is controlled so that the density of a patch may meet a specified target value in specified timing by allowing the image forming means to form the patch as the toner image for measuring density and allowing the density measuring means to measure the density of the patch, and a target correction means correcting the target value based on image forming operation other than the density control operation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

表１は、この実験結果を示すものである。画像密度が高くないＫ色は画像密度「低」「高」ともほとんど同じトナー濃度となった。また、画像密度が比較的高いが設定値「ｍ」には達しないＭ色の場合、画像密度「高」は画像密度「低」よりトナー濃度ＴＣが低下するが、本発明の適用の有無では差は見られなかった。一方、画像密度が設定値「ｍ」を大きく上回るＹ色・Ｃ色の場合、画像密度「高」は画像密度「低」よりトナー濃度ＴＣが大きく低下するが、本発明を適用した場合は、適用しない場合に比べてトナー濃度ＴＣが約２％上昇していることが判る。
【００７８】
そして、本発明を適用してプリントした画像は画像密度「低」「高」の場合とも良好な結果が得られたが、本発明を適用せずプリントした画像は画像密度「高」のとき特にＣ色でトナー濃度ＴＣの低下による画像乱れが見られた。
【００７９】
【発明の効果】
以上詳細に説明したように、本発明によれば、出力される画像の特性（高密度画像か低密度画像かの別など）に影響されることなく安定的に高品質のトナー像を生産性を維持しつつ出力することが出来る画像形成装置を安価に提供することができる。
【図面の簡単な説明】
【図１】図１は、本発明の実施態様に係るフルカラープリンタの断面概略図である。
【図２】図２は、図１に示すフルカラープリンタの画像形成部をより詳細に説明するものである。
【図３】図３は、最終転写ロールの断面を説明するものである。
【図４】図４は、最終転写ロールの周辺構成を詳細に説明するものである。
【図５】図５は、光学濃度センサ本体の構成及び動作を説明するものである。
【図６】図６は、図１に示すフルカラープリンタの画像形成条件制御系説明する機能ブロック図である。
【図７】図７は、電位プロセスコントロールモードの動作を説明するフローチャートである。
【図８】図８は、最終転写ロール上に形成されるトナーパッチを説明するものである。
【図９】図９は、光学濃度センサ本体の構成及び動作を説明するものである。
【図１０】図１０は、帯電電位及び現像バイアス電位の調整を説明するものである。
【図１１】図１１は、ＴＣプロセスコントロールモードの動作を説明するフローチャートである。
【図１２】図１２は、ＴＣプロセスコントロールモードの所定濃度Ｔの補正手順を説明するフローチャートである。
【符号の説明】
１００…フルカラープリンタ（画像形成装置）、１…画像形成ユニット（画像形成手段）、６…コントロールユニット、６０…画像形成条件制御部（濃度制御手段、目標補正手段）、６１…主制御部（検知手段、濃度制御手段）、１２…露光装置ユニット（画像形成手段）、１４…トナーカートリッジ（画像形成手段）、１５…トナー供給フレキシブルパイプ（画像形成手段）、１０…感光体ドラム（像担持体）、１１…帯電ロール、１３…現像装置（画像形成手段）、１３０…現像ロール、２１…一次中間転写ドラム（一次中間転写体）、２２…二次中間転写ドラム（二次中間転写体）、３０…最終転写ロール（最終転写体）、７…光学濃度センサ（検知手段）、７０ａ…発光素子、７０ｂ…受光素子、８…環境センサ、９…表示パネル（表示手段）、Ｐ…トナーパッチ（画像濃度制御用検知パッチ又はトナー濃度制御用検知パッチ）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus using an electrophotographic system (electrostatic transfer system) such as a copying machine, a printer, a facsimile machine, or a multifunction machine of these, and more particularly to an improvement in density control technology of the image forming apparatus.
[0002]
[Prior art]
[Patent Document 1] Japanese Patent Laid-Open No. 2002-365944
[0003]
2. Description of the Related Art Conventionally, image forming apparatuses such as copying machines and printers using an electrophotographic system (electrostatic transfer system) are widely known. The toner density control of the conventional image forming apparatus using the two-component development is based on a so-called pixel count method in which the output image density is measured and a necessary toner amount corresponding to the density is supplied to the developing apparatus. . However, since this pixel count method has a large error, it is common to use a method for forming a toner density measurement patch at a predetermined interval and adjusting the amount of toner to be supplied according to the patch density. (See Patent Document 1).
[0004]
[Problems to be solved by the invention]
However, it has been clarified that the above method may cause variations in the toner density to be controlled depending on the image density of the output image. That is, if images with low image density are output continuously, the toner charge amount to be controlled increases and the toner density increases. Conversely, if images with high image density are output continuously, the toner charge amount decreases and the toner That is, the concentration will decrease.
[0005]
This is due to the fact that the developing device has also been downsized due to the recent downsizing of the apparatus. When the developing unit is downsized, not only the amount of developer in the developing unit is reduced, but also the internal mechanism is simplified, so that the toner is easily consumed without being sufficiently charged. When images having a low image density are continuously printed, less toner is consumed, so that the toner in the developing device has a longer stirring time with the developer and the amount of charge increases. Therefore, when toner density adjustment (control) is performed, the toner density is increased in an attempt to reduce the toner charge amount.
[0006]
On the other hand, when images with a high image density are continuously printed, the amount of toner consumed is large, so that the toner supplied to the developing device is consumed without being sufficiently charged, and the toner charge amount in the developing device decreases. Therefore, when toner density adjustment (control) is performed, the toner density is lowered to increase the toner charge amount. However, toner that is not partly developed remains selectively on the developing roll, and this toner passes through the trimmer section many times, resulting in high charge, so that the toner charge amount on the developing roll appears to be high.
[0007]
As a result, when low-density images are continuously output, toner cloud is likely to occur due to an increase in toner density, which may cause fogging and in-machine contamination. Further, when high-density images are continuously output, image quality may be deteriorated due to deterioration in transferability due to a decrease in toner charge amount, carrier photoconductor adhesion due to toner concentration decrease, and image omission due to insufficient toner supply may occur.
[0008]
The present invention has been made in view of such technical problems, and the object thereof is stable without being affected by the characteristics of an output image (such as whether it is a high-density image or a low-density image). In particular, an image forming apparatus capable of outputting a high-quality toner image while maintaining productivity is provided at low cost.
[0009]
[Means for Solving the Problems]
That is, the present invention includes an image forming unit that includes a developing unit and forms a toner image on a carrier, a density measuring unit that measures the density of the toner image, and a patch as a toner image for density measurement on the image forming unit. A density control unit that performs a density control operation at a predetermined timing to form and control the amount of toner supplied to the developing unit so that the density measurement unit measures the density of the patch, and the density reaches a predetermined target value; The image forming apparatus includes a target correcting unit that corrects the target value based on an image forming operation other than the density control operation.
[0010]
Here, the target correction means can be configured to correct the target value based on the image density during the image forming operation (between one density control operation and the next density control operation). Specifically, the target correction unit increases the toner density when the image density during the image forming operation (between one density control operation and the next density control operation) is higher than a reference value. If the image density during the image forming operation (between one density control operation and the next density control operation) is lower than the reference value, the toner density is reduced. The target value can be corrected.
[0011]
Further, the target correction means can be configured to correct the target value based on the toner charge amount during the image forming operation (between one density control operation and the next density control operation). . Specifically, the target correction means determines that the toner density is higher when the charge amount of the toner during the image forming operation (between one density control operation and the next density control operation) is higher than a reference value. When the target value is corrected so as to be high, and the toner charge amount during the image forming operation (between one density control operation and the next density control operation) is lower than the reference value, the toner density is The target value can be corrected so as to be lower.
[0012]
The image forming means includes four photoconductors corresponding to yellow, cyan, magenta, and black, a first primary intermediate transfer member in contact with two of the four photoconductors, and the remaining two. A second primary intermediate transfer member in contact with the photoconductor, one secondary intermediate transfer member in contact with the first and second primary intermediate transfer members, and a final transfer member in contact with the secondary intermediate transfer member; It can comprise.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0014]
Embodiment FIG. 1 shows a full-color printer 100 as an image forming apparatus according to an embodiment of the present invention. FIG. 2 shows in more detail the main part of image formation of the full-color printer 100 shown in FIG. In addition, the arrow in FIG. 2 has shown the rotation direction of each rotation member. The basic configuration of the image forming apparatus and the operation of the image forming mode will be described below.
[0015]
As shown in FIG. 1, the full-color printer 100 is roughly composed of a printer main body 101 and a paper feed tray unit 102. The printer main body (image forming means) 101 includes image forming unit 1, exposure device unit 12, toner cartridges 14Y to K for yellow Y, magenta M, cyan C, and black K, and toner cartridges 14Y to 14K. The toner supply flexible pipes 15Y to 15K, the control unit 6, the power supply unit 5, and the fixing unit 4 are provided.
[0016]
Also, from the paper feed tray 102 to the paper discharge tray 103 of the printer main body 101, a feed roll pair 41, a first transport roll pair 42, a registration roll pair 43, a second transport roll pair 45 (in the fixing unit 4), a third A conveyance roll pair 46 and a discharge roll pair 47 are provided.
[0017]
Further, as shown in FIG. 2, the image forming unit 1 of the printer main body 101 includes photosensitive drums (image carriers) 10Y to 10K corresponding to the respective colors of yellow Y, magenta M, cyan C, and black K, and these photosensitive members. Charging rolls 11Y-K for primary charging that come into contact with the drums 10Y-K, developing devices (two-component developing means) 13Y-K corresponding to the respective colors, and two of the four photosensitive drums 10Y-K. The first primary intermediate transfer drum 21a in contact with the body drums 10Y and 10M, the second primary intermediate transfer drum 21b in contact with the other two photosensitive drums 10C and K, and the first and second primary intermediate transfer drums. The main part is composed of a secondary intermediate transfer drum 22 that contacts the drums 21 a and 21 b and a final transfer roll (final transfer body) 30 that contacts the secondary intermediate transfer drum 22. The final transfer roll 30 is configured to be detachable from the printer main body 101.
[0018]
The photosensitive drums 10Y to 10K are arranged at a constant interval so as to have a common tangential plane M 1. Further, the first primary intermediate transfer drum 21a and the second primary intermediate transfer drum 21b have a surface target relationship in which each rotation axis is parallel to the photosensitive drums 10Y to 10K and a predetermined target surface is a boundary. It is arranged to be. Further, the secondary intermediate transfer drum 22 is arranged so that the rotational axes thereof are parallel to the photosensitive drums 10Y to 10K.
[0019]
A signal corresponding to the image information for each color is rasterized by an image processing unit (not shown) and input to the exposure apparatus unit 12. In this exposure apparatus unit 12, laser beams 12Y to 12K corresponding to the respective colors of yellow Y, magenta M, cyan C, and black K are modulated and irradiated to the corresponding photosensitive drums 10Y to 10K.
[0020]
Around each of the photosensitive drums 10Y to 10K, an image forming process for each color is performed by a known electrophotographic method. First, as the photoconductor drums 10Y to 10K, for example, photoconductor drums using an OPC photoconductor having a diameter of 20 mm are used, and these photoconductor drums 10Y to 10K rotate at a rotation speed of 95 mm / sec, for example. Driven. As shown in FIG. 2, the surface of the photosensitive drums 10 </ b> Y to 10 </ b> K is charged to about −300 V, for example, by applying a DC voltage of about −840 V to charging rolls 11 </ b> Y to K as contact type charging devices. Is done. The contact-type charging device includes a roll type, a film type, a brush type, and the like, but any type may be used. In this embodiment, a charging roll generally used in an electrophotographic apparatus in recent years is employed. Further, in order to charge the surfaces of the photoconductor drums 10Y to 10K, in this embodiment, a charging method in which only DC is applied is used, but a charging method in which AC + DC is applied may be used.
[0021]
Thereafter, the surfaces of the photosensitive drums 10Y to 10K are irradiated with laser beams 12Y to 12K corresponding to the respective colors of yellow Y, magenta M, cyan C, and black K by a laser optical unit (not shown) as an exposure device. An electrostatic latent image corresponding to the input image information is formed. When the electrostatic latent image is written by the laser optical unit, the surface potential of the image exposure portion of the photosensitive drums 10Y to 10K is neutralized to about −60V or less.
[0022]
The electrostatic latent images corresponding to the colors of yellow Y, magenta M, cyan C, and black K formed on the surfaces of the photosensitive drums 10Y to 10K are developed by the corresponding color developing devices 13Y to 13K. The toner images are visualized as toner images of the respective colors on the photosensitive drums 10Y to 10K.
[0023]
The developing devices 13Y to 13K are filled with two-component developers including toners of different colors, yellow Y, magenta M, cyan C, and black K, and a carrier. As the type of toner used, pulverized toner and spherical toner are conceivable, but in this embodiment, spherical toner is used. Note that an irregularly shaped toner such as pulverized toner has a large contact surface with respect to the adhesion surface, and therefore has a large adhesion force and is difficult to transfer to the transfer destination surface. On the other hand, since spherical toner has a small contact surface with respect to the adhesion surface, the adhesion force is small and the transfer efficiency is high. As a method for producing a spherical toner, a method of subjecting a toner produced by an emulsion polymerization method, a suspension polymerization method, a dissolution suspension method or a kneading pulverization method to a heat treatment is known. The spherical toner refers to toner having M1 ≦ 125, preferably M1 ≦ 120, when the shape factor M1 is expressed by the following equation. M1 = (π · dmax2 / 4A) × 100 (dmax: maximum toner diameter, A: cross-sectional area of toner)
[0024]
These developing devices 13Y to 13K are replenished with toner of each color from the toner cartridges 14Y to 14K shown in FIG. The replenished toner is sufficiently agitated with the carrier by the auger 133 and frictionally charged to a negative polarity. Inside the developing roll 130, a magnet roll (not shown) having a plurality of magnetic poles arranged at a predetermined angle is arranged in a fixed state. By the paddle 132 that conveys the developer to the developing roll 130, the amount of the developer conveyed to the vicinity of the surface of the developing roll 130 is regulated by the developer amount regulating member 131. In this embodiment, the amount of the developer on the developing roll 130 is 30 to 50 g / m. ² At this time, the charge amount of the toner existing on the developing roll 130 is about 20 to 35 μC / g.
[0025]
The toner supplied onto the developing roll 130 is in the form of a magnetic brush composed of a carrier and toner by the magnetic force of the magnet roll, and this magnetic brush is in contact with the photosensitive drums 10Y to 10K. A developing bias voltage of AC + DC is applied to the developing roll 130 to develop the toner on the developing roll 130 into an electrostatic latent image formed on the photosensitive drums 10Y to 10K, thereby forming a toner image. In this embodiment, the development bias voltage has an AC component of 4 kHz and 1.5 kVpp, and a DC component of about −200V.
[0026]
Next, the toner images of the respective colors of yellow Y, magenta M, cyan C, and black K formed on the photosensitive drums 10Y to 10K are converted into the first primary intermediate transfer drum 21a and the second primary intermediate transfer drum. The primary transfer is electrostatically performed on 21b. That is, the yellow Y and magenta M toner images formed on the photosensitive drums 10Y and 10M are cyan C and black K formed on the photosensitive drums 10C and K on the first primary intermediate transfer drum 21a. The color toner images are primarily transferred onto the second primary intermediate transfer drum 21b. Accordingly, on the first primary intermediate transfer drum 21a, the single color image transferred from either the photosensitive drum 10Y or 10M and the two color toner images transferred from both the photosensitive drums 10Y and 10M are superimposed. A double color image is formed. In addition, similar single color images and double color images are formed on the second primary intermediate transfer drum 21b from the photosensitive drums 10C and 10K.
[0027]
The surface potential necessary for electrostatically transferring the toner images from the photosensitive drums 10Y to 10K onto the first and second primary intermediate transfer drums 21a and 21b is about +250 to 500V. This surface potential is set to an optimum value depending on the charged state of the toner, the ambient temperature, and the humidity. The ambient temperature and humidity can be easily known by detecting the resistance value of a member having a characteristic that the resistance value varies depending on the ambient temperature and humidity. As described above, when the charge amount of the toner is in the range of 20 to 35 μC / g and is in a normal temperature and humidity environment, the surface potentials of the first and second primary intermediate transfer drums 21a and 21b are: About + 400V is desirable.
[0028]
The first and second primary intermediate transfer drums 21a and 21b used in this embodiment are, for example, formed with an outer diameter of 42 mm and an electric resistance value R of 10. ⁸ It is set to about Ω. The first and second primary intermediate transfer drums 21a and 21b are single-layered or multiple-layered cylindrical rotating bodies whose surfaces are flexible or elastic, and are generally made of Fe, Al, or the like. A low resistance elastic rubber layer (R = 10) typified by conductive silicone rubber or the like on a metal pipe as a metal core. ² -10 ³ Ω) is provided in a thickness of about 0.1 to 10 mm. Furthermore, the outermost surfaces of the first and second primary intermediate transfer drums 21a and 21b are typically high release layers (R = 10) having a thickness of 3 to 100 μm of fluororubber in which fluororesin fine particles are dispersed. ⁵ -10 ⁹ Ω) and bonded with a silane coupling agent-based adhesive (primer).
[0029]
What is important here is the resistance value and the releasability of the surface, and the resistance value of the high release layer is R = 10. ⁵ -10 ⁹ The material is not particularly limited as long as it is about Ω and has a high releasability. The first and second primary intermediate transfer drums 21a and 21b are respectively attached with first and second primary cleaning rollers 23a and 23b so as to be driven to rotate. Each of these primary cleaning rolls 23a and 23b is configured by covering a metal roll body with a flocking tape of a conductive brush, and a predetermined cleaning bias is applied thereto.
[0030]
The single-color or double-color toner images formed on the first and second primary intermediate transfer drums 21 a and 21 b in this way are electrostatically secondary-transferred onto the secondary intermediate transfer drum 22. Accordingly, a final toner image from a single color image to a quadruple color image of yellow Y, magenta M, cyan C, and black K is formed on the secondary intermediate transfer drum 22.
[0031]
The surface potential necessary for electrostatically transferring the toner images from the first and second primary intermediate transfer drums 21a and 21b onto the secondary intermediate transfer drum 22 is about +600 to 1200V. This surface potential becomes an optimum value depending on the charged state of the toner, the ambient temperature, and the humidity, as in the case of transferring from the photosensitive drums 10Y to 10K to the first primary intermediate transfer drum 21a and the second primary intermediate transfer drum 21b. Will be set. Further, since what is necessary for the transfer is a potential difference between the first and second primary intermediate transfer drums 21a and 21b and the secondary intermediate transfer drum 22, the first and second primary intermediate transfer drums 21a and 21b have different potentials. It is necessary to set the value according to the surface potential. As described above, the charge amount of the toner is in the range of 20 to 35 μC / g, is in a normal temperature and humidity environment, and the surface potential of the first and second primary intermediate transfer drums 21a and 21b is about + 400V. In this case, the surface potential of the secondary intermediate transfer drum 22 is set to about + 800V, that is, the potential difference between the first and second primary intermediate transfer drums 21a and 21b and the secondary intermediate transfer drum 22 is set to about + 400V. It is desirable to do.
[0032]
For example, the secondary intermediate transfer drum 22 used in this embodiment has an outer diameter of 42 mm, which is the same as the first and second primary intermediate transfer drums 21a and 21b, and has a resistance value of 10 mm. ¹¹ It is set to about Ω. Similarly to the first and second primary intermediate transfer drums 21a and 21b, the secondary intermediate transfer drum 22 is a single-layered or cylindrical rotating body having a plurality of layers of flexible or elastic surfaces. In general, a low resistance elastic rubber layer (R = 10) represented by conductive silicone rubber or the like on a metal pipe as a metal core made of Fe, Al or the like. ² -10 ³ Ω) is provided in a thickness of about 0.1 to 10 mm. Further, the outermost surface of the secondary intermediate transfer drum 22 is typically formed by forming fluororubber in which fluororesin fine particles are dispersed as a high release layer having a thickness of 3 to 100 μm, and a silane coupling agent-based adhesive. (Primer).
[0033]
What is important here is the resistance value and the releasability of the surface as in the first and second primary intermediate transfer drums 21a and 21b. However, the resistance value of the secondary intermediate transfer drum 22 needs to be set higher than that of the first and second primary intermediate transfer drums 21a and 21b. Otherwise, the secondary intermediate transfer drum 22 will charge the first and second primary intermediate transfer drums 21a and 21b, making it difficult to control the surface potential of the first and second primary intermediate transfer drums 21a and 21b. Become. The material is not particularly limited as long as the material satisfies such conditions. A secondary cleaning roll 24 is attached to the secondary intermediate transfer drum 22 so as to be driven to rotate. The secondary cleaning roll 24 is configured by covering a metallic roll body with a flocking tape of a conductive brush, and a predetermined secondary cleaning bias is applied.
[0034]
Next, the final toner image from the single-color image to the quadruple-color image formed on the secondary intermediate transfer drum 22 is tertiary-transferred onto the paper S passing through the paper transport path P 2 by the final transfer roll 30. The The paper passes through the resist roll pair 43 through a paper feeding process, and is fed into the nip portion between the secondary intermediate transfer drum 22 and the final transfer roll 30. After this final transfer step, the final toner image formed on the paper is fixed by the fixing roll pair 44 in the fixing unit 4, and a series of image forming processes is completed.
[0035]
The final transfer roll 30 has an outer diameter of 20 mm, for example, and a resistance value R of 10 ⁸ It is set to about Ω. As shown in FIG. 3, the final transfer roll 30 is configured by providing a coating layer 32 made of urethane rubber or the like on a metal shaft 31 and applying a coating on the coating layer 32 as necessary. The optimum voltage of the voltage applied to the final transfer roll 30 varies depending on the ambient temperature, humidity, paper type (resistance value, etc.), and is approximately +1200 to 5000V. In this embodiment, a constant current method is employed, and a current of about +10 μA is applied in a reference environment to obtain a substantially appropriate transfer voltage (+1600 to 2000 V).
[0036]
In these series of transfer processes, when the toner image passes through the transfer site of each transfer process, due to Paschen discharge or charge injection, a part of the positive toner in the (−) charged image has a reverse polarity ( +) May become charged toner. Since the (+) charged toner is not transferred to the next process but flows backward upstream, it adheres and accumulates on the charging devices 11Y to 11K having the highest negative potential. The portions of the charging devices 11Y to 11K to which the toner is attached are actively discharged, and the surface potential of the photosensitive drums 10Y to 10K tends to increase. Unevenness occurs in the surface potential of the photoconductive drums 10Y to 10K at a portion where no toner adheres. If unevenness occurs in the surface potential of the photoconductive drums 10Y to 10K, the latent image potential is uneven even if the image is uniformly exposed on the surface of the photoconductive drums 10Y to 10K in order to form an electrostatic latent image. As a result, a difference in development amount occurs, and density unevenness is particularly noticeable when a halftone image is to be developed.
[0037]
Therefore, in order to prevent the occurrence of density unevenness due to the toner adhering to the charging devices 11Y to 11K, in this embodiment, a predetermined timing such as before a printing operation, after a printing operation, or every predetermined number of sheets during continuous printing. The following cleaning operation is performed.
[0038]
The final transfer roll 30 is the most rotating member of the charging devices 11Y to K, the photosensitive drums 10Y to 10K, the first and second primary intermediate transfer drums 21a and 21b, the secondary intermediate transfer drum 22, and the final transfer roll 30. By applying a voltage with a potential gradient in order so that the negative potential is increased, the (+) charged toner having the opposite polarity attached to and deposited on the charging devices 11Y to 11K during the printing operation is removed in the cleaning operation. The toner is transferred and moved sequentially to the final transfer roll 30 and collected by a cleaning device 31 including a final cleaning member 32 such as a blade provided in contact with the final transfer roll 30. As shown in FIG. 4, the cleaning device 31 includes a blade-like final cleaning member 32, a toner recovery box 33, a support frame 34, a static eliminator 35 provided on the support frame 34, and a bias plate 36. ing.
[0039]
In this embodiment, the surface potentials of the charging devices 11Y to 11K are 0V, the surface potentials of the photosensitive drums 10Y to 10K are −300V, the surface potentials of the first and second primary intermediate transfer drums 21a and 21b are −800V, The surface potential of the secondary intermediate transfer drum 22 is set to -1300V, and the surface potential of the final transfer roll 30 is set to -2000V. This potential gradient is obtained by supplying a voltage to the metal parts (shafts and pipes) of each member. For example, the first and second primary intermediate transfer drums 21a and 21b or the secondary intermediate transfer drum 22 are used. When a desired surface potential is obtained by the relationship of the resistance values of these members, the above method may be used. In such a negative application cleaning mode, that is, a (+) charged toner recovery mode having a reverse polarity, it is possible to prevent the occurrence of density unevenness due to the toner adhering to the charging devices 11Y to 11K.
[0040]
Around the cleaning device 31, an optical density sensor (density measuring means) 7 is positioned at an axially central portion of the final transfer roll 30 on the radial extension line on the outer periphery of the final transfer roll 30. Has been placed. The optical density sensor 7 includes a sensor main body 70 and a holder 71 for fixing the sensor main body 70. As shown in FIG. 5A, the optical density sensor 7 is a specular reflection type sensor that detects specular reflection light, and has a predetermined incident angle φ with respect to the detection position on the surface of the final transfer roll 30. In order to detect the specularly reflected light that is irradiated from the light emitting element 70a to the detection position on the surface of the final transfer roll 30 and is regularly reflected from the detection position, It is composed of a light receiving element 70b made of a phototransistor or the like disposed so as to be inclined with respect to a detection position on the surface of the transfer roll 30 by a reflection angle equal to the predetermined incident angle.
[0041]
As the optical density sensor 7, as shown in FIG. 5B, a diffuse reflection type sensor that detects diffused light may be used. Further, both a specular reflection type sensor and a diffuse reflection type sensor may be used. In this case, the toner density detection accuracy can be further improved by detecting the toner density based on both the specular reflection component and the scattered light component.
[0042]
By the way, in the full-color printer 100 according to this embodiment, the optical density sensor 7 is used for density measurement of the toner patch during density control. Since the xerographic method uses static electricity, the image density tends to fluctuate due to environmental changes and aging. For this reason, a process control mode (density control operation) is provided separately from the image formation mode (image formation operation) to control environmental changes, changes with time, etc., and control the electrophotographic process while measuring the toner patch density. It is preferable.
[0043]
The process control mode includes a TC process control mode (toner density control mode) for controlling the toner density (ratio of toner and carrier in the developer) in each of the developing devices 13Y to 13K, and finally on the paper. There is a potential process control mode (image density control mode) for controlling the toner density of the transferred toner image. In any of these process control modes, a test toner patch is formed on the surface of an image density detection medium (image carrier) such as a photosensitive member, an intermediate transfer member, a transfer roll to paper, or a transfer belt. The image density is detected by an optical density sensor and various image forming processes (image forming conditions) are controlled. However, a preferable image density detecting medium differs depending on the characteristics of each process control.
[0044]
In other words, in the TC process control mode, an image density detection medium close to each developing device 13Y-K, for example, each of the developing devices 13Y-K, for example, each so as to be able to detect the toner / carrier ratio in each developing device 13Y-K more accurately. It is preferable to detect toner patches on the surfaces of the photosensitive drums 10Y to 10K. On the other hand, in the potential process control mode, an image density detection medium close to the paper, for example, a toner patch on the surface of the secondary intermediate transfer drum 22 or the final transfer roll 30 is detected so that the toner density on the paper can be detected more accurately. It is preferable to do.
[0045]
However, in order to detect the toner patches on the photosensitive drums 10Y to 10K, it is necessary to provide four optical density detecting units for each of the photosensitive drums 10Y to 10K. Two optical density detectors may be used on the first and second primary intermediate transfer drums 21a and 21b. If it is on the secondary intermediate transfer drum 22 or the final transfer roll 30, one optical density detecting means may be used.
[0046]
Therefore, in this embodiment, the single optical density sensor 7 is used with emphasis on the simplicity of the configuration of the apparatus, and the toner patch on the final transfer roll 30 is detected in both the process control modes. . On the other hand, in the TC process control mode, the ratio of the toner and the carrier in each of the developing devices 13Y to 13K can be detected as accurately as possible (even on the final transfer roll 30 that has undergone a plurality of transfers). For example, the toner amount of the test patch toner image formed on the photosensitive drums 10Y to 10K is 90% or more on the final transfer roll 30 or 95 so that the transfer rate in the TC process control mode is particularly high. It was decided to control the image forming conditions so that the transfer was at least%.
[0047]
FIG. 6 is a block diagram illustrating an image forming condition control system of the full color printer 100 according to the present embodiment.
[0048]
As shown in the figure, this control system is configured with an image forming condition control unit 60 as a center, and an input unit for inputting a signal to the image forming condition control unit 60 is a toner on the final transfer roll 30. In addition to the optical density sensor 7 for measuring the density and the environmental sensor 8 for measuring the temperature and humidity in the full-color printer 100, the main control for inputting the mode, print speed, and other information of the multicolor or single color of the full-color printer 100. Part 61 may be mentioned. The image forming condition control unit 60 and the main control unit 61 are both functionally realized in the control unit 6 of the printer main body 101.
[0049]
On the other hand, the output unit from which the signal is output from the image forming condition control unit 60 includes charging power supply units 110Y to 110K for applying a charging voltage to the charging rolls 11Y to 11K, and laser beams 12Y to 12K corresponding to the respective colors. , The developing power supply units 131Y to 131K for applying a developing bias voltage to the developing rolls 130Y to 130K, the toner supply flexible pipes 15Y to 15K (driving units thereof), the first and the second. Primary transfer power supply units 210a and 210b for applying a primary transfer voltage to the primary intermediate transfer drums 21a and 21b, a secondary transfer power supply unit 220 for applying a secondary transfer voltage to the secondary intermediate transfer drum 22 and a final transfer roll 30. Primary cleaning for applying a primary cleaning voltage to the final transfer power supply unit 300 for applying the final transfer current and the first and second primary cleaning rolls 23a and 23b, respectively. Source unit 230a, b, include secondary cleaning power unit 240 that applies a secondary cleaning voltage to the secondary cleaning roller 24.
[0050]
From the main control unit 61 to the image forming condition control unit 60, the mode of the full-color printer 100 (separate image forming mode, potential process control mode, and TC control mode), printing speed (separate 8PPM or 16PPM), printing color (multiple A signal indicating the color or single color), a signal indicating the toner density of the toner patch P from the optical density sensor 7, and a signal indicating the temperature and humidity in the full-color printer 100 are input from the environment sensor 8. Then, a toner image as an image I is formed on the paper S based on these input signals and the image forming conditions provided in advance in the image forming condition control unit 60. Further, a toner image as the toner patch P1 is formed on the final transfer roll 30 based on these input signals and the image forming condition and toner patch creating condition provided in advance in the image forming condition control unit 60. . Further, a toner image as the toner patch P <b> 2 is formed on the final transfer roll 30 based on these input signals and the image forming condition and toner patch creating condition provided in the image forming condition control unit 60.
[0051]
Here, the condition for determining that the potential process control mode is required by the main control unit 61 is, for example, immediately after the full-color printer 100 is powered on, and a predetermined number of images from the previous potential process control mode. When forming (in the image forming mode), there is a case where there is an explicit instruction from the user. Similarly, a condition for determining that the TC process control mode is necessary for the main control unit 61 is, for example, immediately after the full color printer 100 is turned on, and a predetermined number of images from the previous TC process control mode. When forming (in the image forming mode), there is a case where there is an explicit instruction from the user. Hereinafter, the operation of each control mode will be described in detail.
[0052]
○ Potential process control mode
First, the main control unit 61 prints the full color printer 100 mode (image forming mode, potential process control mode, and TC control mode), and the environment sensor 8 prints the temperature and humidity in the full color printer 100 from the main control unit 61. When signals indicating the speed and the print color are input, the image forming condition control unit 60 selects an appropriate one according to the situation from the image forming conditions and toner patch forming conditions stored in advance.
[0053]
For example, when a signal indicating that the mode is the potential process control mode, the printing speed is 16 PPM, the printing color is multicolor (color), and the temperature and humidity is the reference environment from the environment sensor 8 is input from the main control unit 61. The image forming condition control unit 60 applies the same 400 [V] as the image forming mode to the secondary intermediate transfer drum 22 as the primary transfer potential to be applied to the primary intermediate transfer drums 21a and 21b. The transfer potential is 900 [V], the final transfer current applied to the final transfer roll 30 is 6 [μA], the primary cleaning voltage applied to the primary cleaning rolls 23a and b is 190 [V] as the secondary cleaning voltage. 210 [V] is −300 [V] as the (target) charging potential of the photosensitive drum 10, and −2 as the DC component of the developing bias voltage 0 [V] is selected, respectively. Further, the image forming condition control unit 60 selects coverage input 33.3% as the toner patch creation condition.
[0054]
Based on the image forming conditions and toner patch creation conditions selected in this way, the full-color printer 100 forms a toner image P1 as a toner patch on the final transfer roll 30 and performs potential process control.
[0055]
FIG. 7 is a flowchart for explaining the operation of the potential process control VC. Hereinafter, the operation of the potential process control VC will be described in more detail based on this flowchart.
[0056]
First, in a state where the toner patch P1 is not transferred, the surface of the final transfer roll 30 is detected by the optical density sensor 7, and the output Vcln of the optical density sensor 7 at this time is stored (step ST101). Next, toner patches P1 (Y) to (K) for each color of yellow, magenta, cyan, and black based on the image forming conditions and toner patch creating conditions described above are shown in FIG. Then, it is formed on the final transfer roll 30 (step ST102).
[0057]
FIG. 8A illustrates the toner patch P <b> 1 that is formed at the central portion in the axial direction of the final transfer roll 30. This toner patch P1 is formed in the order of yellow P (Y), cyan P (C), magenta P (M), and black P (K) in the rotational direction of the final transfer roll 30, and the size of each toner patch P1 is 11 [mm] in the sub-scanning direction X and 12 [mm] in the main scanning direction Y, and the interval D between the toner patches P1 is 3 [mm]. In this embodiment, each toner patch P1 is formed at the central portion of the final transfer roll 30 in the axial direction. However, as shown in FIG. But you can. In that case, it is necessary to change the installation position of the optical density sensor 7.
[0058]
Thereafter, the yellow, magenta, cyan, and black toner patches P1 (Y) to (K) formed on the final transfer roll 30 are filled with 0 by the optical density sensor 7 as shown in FIG. 16 points are detected at a pitch of 5 mm to obtain an average value Vpatch (step ST103). Here, a specular reflection type optical density sensor 7 is used as shown in FIG. 9A, but a diffuse reflection type sensor that detects diffused light is used as shown in FIG. 9B. Alternatively, both sensors may be used.
[0059]
A ratio Vpatch / Vcln obtained by dividing the average value of each color by the value of the surface of the final transfer roll 30 (the state where the toner patch P1 is not transferred) is used as a substitute value of density (step ST104). Here, the reason for taking the ratio with the value of the bare transfer surface of the final transfer roll 30 is to correct the change in the reflectance of the bare transfer surface of the final transfer roll 30 and the variation in the amount of emitted LED light.
[0060]
As a result, Vpatch / Vcln is compared with a predetermined value for each color (step ST105), and when the obtained density of the toner patch P1 is lower than the predetermined density, the image forming condition control unit 60 develops according to the difference. DC component of bias voltage V _dc At the same time (as a result of increasing the absolute value of the voltage applied to the charging roll 11) and the charging potential V of the photosensitive drum 10 _h Is made larger (step ST106). As a result, as shown in FIG. 10B, the electric field in the developing direction formed between the developing roll 130 and the image portion on the photosensitive drum 10 is increased, and the amount of toner to be developed is increased. The image density increases.
[0061]
On the contrary, if the obtained density of the toner patch P1 is higher than the predetermined density, the image forming condition control unit 60 determines the DC component V of the developing bias voltage according to the difference. _dc At the same time (as a result of lowering the absolute value of the voltage applied to the charging roll 11) and the charging potential V of the photosensitive drum 10 at the same time. _h Is made smaller (step ST106). As a result, as shown in FIG. 10C, the electric field in the developing direction formed between the developing roll 130 and the image portion on the photosensitive drum 10 is reduced, and the amount of toner to be developed is reduced. The image density decreases.
[0062]
○ TC process control mode
In the toner replenishment, the image density is measured from the print image signal, and the replenishment time is controlled so as to replenish the toner corresponding to the amount of toner used according to the result. However, in this method, when the development amount varies, the amount of toner used varies, and the balance with the replenished toner amount deviates, and the toner density in the developing device 13 varies. Therefore, the toner patch P2 is created to detect the density, and the toner replenishment amount is corrected according to the result.
[0063]
First, the main control unit 61 prints the full color printer 100 mode (image forming mode, potential process control mode, and TC control mode), and the environment sensor 8 prints the temperature and humidity in the full color printer 100 from the main control unit 61. When signals indicating the speed and the print color are input, the image forming condition control unit 60 selects an appropriate one according to the situation from the image forming conditions and toner patch forming conditions stored in advance.
[0064]
For example, when a signal indicating that the mode is the potential process control mode, the printing speed is 16 PPM, the printing color is multicolor (color), and the temperature and humidity is the reference environment from the environment sensor 8 is input from the main control unit 61. The image forming condition control unit 60 sets 360 [V] as the primary transfer potential to be applied to the primary intermediate transfer drums 21a and 21b and 810 [V] as the secondary transfer potential to be applied to the secondary intermediate transfer drum 22 for the image forming conditions. ] As a final transfer current applied to the final transfer roll 30, 190 [V] as a primary cleaning voltage applied to the primary cleaning rolls 23 a and b, 210 [V] as a secondary cleaning voltage, Select -289 [V] as the (target) charging potential of the photosensitive drum 10 and -200 [V] as the DC component of the developing bias voltage. To. Further, the image forming condition control unit 60 selects coverage input 100% as the toner patch creation condition.
[0065]
Based on the image forming conditions and toner patch creation conditions selected in this way, the full-color printer 100 forms a toner image P2 as a toner patch on the final transfer roll 30 and performs TC process control.
[0066]
FIG. 11 is a flowchart for explaining the operation of the TC process control. Hereinafter, the operation of the TC process control will be described in more detail based on this flowchart.
[0067]
First, the image forming condition control unit 60 detects the surface of the final transfer roll 30 with the optical density sensor 7 in a state where the toner patch P2 is not transferred, and stores the output Vcln of the optical density sensor 7 at this time. (Step ST201). Next, toner patches P2 (Y) to (K) are shown in FIG. 8A for each color of yellow, magenta, cyan, and black based on the image forming conditions and toner patch creating conditions described above. Then, it is formed on the final transfer roll 30 (step ST202). Here, unlike the image forming mode and the potential process control mode, in this TC process control mode, the development bias voltage is developed with only the DC component, and the AC component is not superimposed.
[0068]
Thereafter, 16 points are detected in the yellow, magenta, cyan, and black toner patches P2 (Y) to (K) by the optical density sensor 7 at a pitch of 0.5 mm, as shown in FIG. 9A. The average value Vpatch is obtained (step ST203). Here, a specular reflection type optical density sensor 7 is used as shown in FIG. 9A, but a diffuse reflection type sensor that detects diffused light is used as shown in FIG. 9B. Alternatively, both sensors may be used.
[0069]
Then, the ratio Vpatch / Vcln obtained by dividing the average value of each color by the value of the surface of the final transfer roll 30 (the state where the toner patch P2 is not transferred) is used as a substitute value of density (step ST204).
[0070]
As a result, when the obtained toner patch density is lower than the predetermined density T: Target (target value), the image forming condition control unit 60 has a low toner density. Is measured (step ST210), and the toner supply amount is corrected to be larger than the determined toner supply amount (step ST220) (step ST206). On the other hand, if the test patch is higher than the predetermined density, the image forming condition control unit 60 has a high toner density. Therefore, the image density is determined from the print image signal in advance according to the difference (step ST210). Correction is made so that the toner replenishment amount is decreased below the toner supply amount (step ST220) (step ST208).
[0071]
Here, for example, when the density of the toner patch P2 is lower than the predetermined density T, the image forming condition control unit 60 sets the drive time of the drive unit of each of the toner supply flexible pipes 15Y to 15K to be longer than a specified time. The drive unit of each pipe 15Y-K is controlled (see FIG. 6).
[0072]
○ Correction of predetermined density T
As a result of further studies by the present inventors, it has been found that there is a possibility that the toner density varies in the TC process control mode. That is, when images with low image density are output continuously, the controlled toner charge amount decreases and the toner density increases, and conversely when images with high image density are output continuously, the toner charge amount increases and the toner is increased. That is, the concentration will decrease. Therefore, in the present embodiment, the following correction of the predetermined density T is performed.
[0073]
FIG. 12 is a flowchart for explaining the correction operation of the predetermined density T. That is, in this full-color printer 100, the image forming condition control unit 60 calculates the average image density M of the image output from the previous TC process control mode (i) to the next TC process control mode (i + 1) for each color. It is calculated every time (ST301). Then, in the next TC process control mode (i + 1), the obtained average image density M is compared with set values m1 and m2 recorded in advance in NVRAM (S302).
[0074]
Here, when the average image density M is not more than the set value m1 and not less than the set value m2 (m2 ≦ M ≦ m1), the predetermined density T remains as it is (T = T) (ST304). On the other hand, when the average image density M is higher than the set value m1 (m1 <M), the predetermined density T is updated to a value (T = T−t1: t1> 0) obtained by subtracting the set value t1 recorded in advance in NVRAM. (ST303). On the other hand, when the average image density M is lower than the set value m2 (M <m2), the predetermined density T is updated to a value (T = T + t2: t2> 0) obtained by adding the set value t2 previously recorded in NVRAM. (ST305). At this time, the predetermined density T is such that the lower the value, the higher the toner density, and the higher the value, the lower the toner density.
[0075]
In this embodiment, the setting value m1 is set to a numerical value that is about 20% and the setting value t1 is about 2%. 20% of the setting value m1 represents the average image density between Patch and Patch. 2% of the set value t1 represents the fluctuation of the toner density TC. In other words, when the average image density between Patch and Patch exceeds 20%, the target toner density target is changed so that the toner density TC is increased by 2% from the conventional level.
In this example, m2 and t2 are not set. It can also be said that either m2 or t2 is set to 0%.
[0076]
Experiment
In the full-color printer 100 according to the present embodiment, the following experiment was performed in order to confirm the effect of correcting the predetermined density T. First, in the full color printer 100 according to the present embodiment, 1000 images (image density “low”) having an average image density of 1% for each color, and then the average image density of each color is Y: 40%, M: 1000 images (image density “high”) such that 18%, C: 41%, and K: 4% were run. The high image density image running was performed when the present invention was implemented (when the predetermined density T was corrected) and when it was not implemented (when the predetermined density T was not corrected).
[0077]
[Table 1]

Table 1 shows the results of this experiment. The color of K, which is not high in image density, has almost the same toner density for both “low” and “high” image densities. In the case of M color, which has a relatively high image density but does not reach the set value “m”, the image density “high” has a lower toner density TC than the image density “low”. There was no difference. On the other hand, in the case of Y color / C color where the image density is much higher than the set value “m”, the toner density TC is much lower than the image density “low” in the image density “high”, but when the present invention is applied, It can be seen that the toner concentration TC is increased by about 2% as compared with the case where it is not applied.
[0078]
The image printed by applying the present invention gave good results even when the image density was “low” and “high”, but the image printed without applying the present invention was particularly high when the image density was “high”. In C color, image disturbance due to a decrease in toner density TC was observed.
[0079]
【The invention's effect】
As described above in detail, according to the present invention, a high-quality toner image can be stably produced without being affected by the characteristics of an output image (such as whether it is a high-density image or a low-density image). Therefore, it is possible to provide an image forming apparatus that can output while maintaining the above.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a full-color printer according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining the image forming unit of the full-color printer shown in FIG. 1 in more detail.
FIG. 3 illustrates a cross section of a final transfer roll.
FIG. 4 is a diagram illustrating in detail the peripheral configuration of the final transfer roll.
FIG. 5 illustrates the configuration and operation of an optical density sensor main body.
6 is a functional block diagram for explaining an image forming condition control system of the full-color printer shown in FIG. 1. FIG.
FIG. 7 is a flowchart for explaining an operation in a potential process control mode;
FIG. 8 illustrates a toner patch formed on a final transfer roll.
FIG. 9 illustrates the configuration and operation of an optical density sensor main body.
FIG. 10 illustrates adjustment of a charging potential and a developing bias potential.
FIG. 11 is a flowchart illustrating an operation in a TC process control mode.
FIG. 12 is a flowchart illustrating a procedure for correcting a predetermined density T in a TC process control mode.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100 ... Full color printer (image forming apparatus), 1 ... Image forming unit (image forming means), 6 ... Control unit, 60 ... Image forming condition control part (density control means, target correction means), 61 ... Main control part (detection) , Exposure control unit (image forming means), 14 ... toner cartridge (image forming means), 15 ... toner supply flexible pipe (image forming means), 10 ... photosensitive drum (image carrier). DESCRIPTION OF SYMBOLS 11 ... Charging roll, 13 ... Developing apparatus (image forming means), 130 ... Developing roll, 21 ... Primary intermediate transfer drum (primary intermediate transfer member), 22 ... Secondary intermediate transfer drum (secondary intermediate transfer member), 30 ... last transfer roll (final transfer body), 7 ... optical density sensor (detection means), 70a ... light emitting element, 70b ... light receiving element, 8 ... environmental sensor, 9 ... display panel ( Display means), P ... toner patch (the image density control detection patch or toner concentration control detection patch)

Claims (10)

Image forming means for forming a toner image on the carrier including developing means;
Density measuring means for measuring the density of the toner image;
The image forming unit forms a patch as a toner image for density measurement, the density measuring unit measures the density of the patch, and controls the amount of toner supplied to the developing unit so that the density becomes a predetermined target value. Concentration control means for performing the concentration control operation at a predetermined timing;
An image forming apparatus comprising: a target correcting unit that corrects the target value based on an image forming operation other than the density control operation. The image forming apparatus according to claim 1, wherein the target correcting unit corrects the target value based on an image density during an image forming operation. The image forming apparatus according to claim 1, wherein the target correction unit corrects the target value based on an image density during an image forming operation between one density control operation and a next density control operation.
Since claim 4 is missing, please raise the following claim. The image forming apparatus according to claim 2, wherein the target correction unit corrects the target value so that the toner density becomes high when the image density during the image forming operation is higher than a reference value. The image forming apparatus according to claim 2, wherein the target correction unit corrects the target value so that the toner density is low when the image density during the image forming operation is lower than a reference value. The image forming apparatus according to claim 1, wherein the target correcting unit corrects the target value based on a charge amount of toner during an image forming operation. The image forming apparatus according to claim 1, wherein the target correcting unit corrects the target value based on a charge amount of toner during an image forming operation between one density control operation and a next density control operation. The image forming apparatus according to claim 6, wherein the target correction unit corrects the target value so that the toner density becomes high when the charge amount of the toner during the image forming operation is higher than a reference value. The image forming apparatus according to claim 6, wherein the target correction unit corrects the target value so that the toner density becomes low when the charge amount of the toner during the image forming operation is lower than a reference value. As the image forming means, four photoconductors corresponding to each color of yellow, cyan, magenta, and black, a first primary intermediate transfer member in contact with two of the four photoconductors, and the remaining two photoconductors A second primary intermediate transfer member in contact with the first intermediate transfer member, a first secondary intermediate transfer member in contact with the first and second primary intermediate transfer members, and a final transfer member in contact with the secondary intermediate transfer member. The image forming apparatus according to claim 1.

Images