JP3742446B2 - Method for controlling image forming apparatus - Google Patents

Description

実際のトナー補給時間Ｘ（sec）は求めたトナー補給量をＴadd（mg)、トナー補給モータの補給能力をＫ（mg/sec）とすると、
Ｘ＝Ｔadd／Ｋ
で表され、上記条件のときのＴona１〜３が、求めたトナー補給量Ｔaddに相当する。
【００６８】
これにより、トナー補給に用いる、顕像化後のパターン濃度はトナー補給の追従する範囲で維持されるが、経時の環境変動などにより、同じトナー濃度でも現像能力が異なることがあるため、次第にトナー濃度が好ましい濃度範囲（例えば、４〜７wt％）から外れて上昇あるいは下降してしまうことが考えられる。
【００６９】
一般に、現像特性線の傾きは、トナー濃度が高くなると大きくなり、また、絶対湿度が低くなると小さくなっていくという性質がある。
【００７０】
そこで、本発明においてはこの性質を考慮し、トナー濃度が所定の範囲にあるように現像特性と環境特性とから、現像特性線の傾きが大きく、望ましくは、絶対湿度の低い場合、トナー濃度が低下するように変更し、また、現像特性線の傾きが小さく、望ましくは、絶対湿度の高い場合、トナー濃度が上昇するように、トナー補給制御に用いる潜像パターンの現像ポテンシャルを変更する。
例えば、電位制御ａの結果、現像特性線の傾きが大きく、望ましくは、絶対湿度の低いと判断された場合、トナー濃度が低下するようにその程度に応じて、電位制御ｂの０．４mgを狙っている潜像パターンの現像ポテンシャルを数十Ｖ大きくする。これにより、潜像パターン上のトナー付着量は上昇するため、トナー補給量は抑えられ、トナー濃度が低下する。
【００７１】
なお、反射濃度センサ２０８がトナーの低付着量領域から高付着量領域まで同程度の感度を有していれば、特に湿度センサを設けなくても、検出された検出値に基づいてトナー濃度、画像濃度を制御できる。しかしながら、一般的に、反射濃度センサは、トナーの高付着量領域で感度が低いため、中程度の付着量域で検出された検出値を基に、高付着量領域の付着量を予想している。また、温度や湿度などの環境の変動、特に湿度に大きな変動があると、トナーの帯電量（Ｑ／Ｍ）に影響し、パッチパターン部のトナー付着量が変動するので、この予測がしにくくなる。このため、湿度センサ等の環境変動を検知できるセンサを用いた方が、絶対湿度の条件を考慮してトナー付着量を検出するためには望ましく、トナー濃度、画像濃度を制御するのに有利なことが多い。
【００７２】
ここで、環境の変動を検知するセンサを持っていないために環境変動の検知ができない場合には、電位制御ａの結果による現像特性線の傾き、すなわち、選択された電位制御テーブルのナンバーによって、現像特性線の傾きが所定の傾きよりも大きかったり、小さかったりしたときに、同様に電位制御ｂのトナー補給制御に用いている潜像パターンの現像ポテンシャルを現像特性線の傾きが大きい場合には大きく、小さい場合には小さくする。これによれば、環境の変動を考慮できる場合に比してトナー濃度変動量が若干増えるものの、ある程度のトナー濃度範囲に抑えることができる。
【００７３】
以上、本実施形態のトナー補給制御方法によれば、通常このような制御を行うと、電位制御ａだけでは次の現像特性の測定まではトナー濃度が変化すると、画像も変化してしまうのに対し、画像形成時に毎回電位制御を行っている電位制御ｂによって各電位が制御されるので、トナー濃度変化のような短いレンジの変化に追従して安定した画像を得ることができる。
【００７４】
特に、本実施形態のトナー補給制御方法では、現像特性を装置内において直接検出しているので、最適な画像電位を得ることができるとともに、最適なトナ−濃度制御条件を決定することができる。これにより、その時点での最良な画像を保証することができる。
また、現像特性として、感光体ドラム１０３上の潜像電位とトナ−付着量との関係が直線特性を示す領域における直線方程式を用いて現像特性として用いるため、計算精度の安定性を得ることができるとともに、制御ル−チンを簡明に構成することができる。
また、感光体ドラム１０３上のトナ−付着量を検出する反射濃度センサ２０８を現像特性の算出とトナ−補給との両方に用いることができるので、センサの数を必要最小限に抑えることができる。これにより構成が簡単になり、コスト面でも非常に有利である。とりわけ、フルカラ−システムの構成時において、トナ−濃度制御の各色ごとのトナ−濃度制御用にセンサをそれぞれ持たせる必要が無いので、非常に有利である。
【００７５】
なお、本実施形態のトナー補給制御方法においては、潜像パターン形成時の現像バイアスを、算出した現像特性（現像剤の特性変動の影響を受けている）を前提にして、黒トナーの場合は０．４mg／cm²、カラートナーの場合は０．３mg／cm²の付着量が得られるように補正するため、逆にトナー濃度が許容範囲の下限に近づいた場合にも、ある程度のパターンへのトナー付着量を得るようにしている。このため、現実のトナー濃度のわりにトナー補給量が少なくなり、トナー濃度が過剰な低下を生じる恐れがある。しかし、このような恐れは、従来周知の最適のトナー補給量を確保する各種の技術、例えば、画像データを用いてトナー消費量を予測し、予測したトナー消費量をトナー補給量設定に当たって参考にする技術を併用することによって無くすことができる。無論、本実施形態の装置においても、このような技術が採用されている。
（以下、余白）
【００７６】
【発明の効果】
請求項１記載の発明によれば、第一制御を行う周期よりも短い周期で行う第二制御で形成する潜像パターンの総数は、起動時に行う第一制御で形成する潜像パターンの総数よりも少数なので、第一制御で形成する潜像パターンの数と同数のパターンを形成する場合に比して、パターン形成時間を短くすることができるとともに、パターン顕像化に伴うトナー消費を少なくできる。しかも、起動時に求めた上記現像γ特性線の直線区間に内にある潜像パターンを用いるので、起動時よりも少ない数の潜像パターンを形成するわりには現像特性を正確に把握することができる。
よって、各種電位制御を精度良く行うことができ、現像剤の変動に対して画像再現に最適である。
【図面の簡単な説明】
【図１】本発明を適用できる画像形成装置の一例を示す概略構成図である。
【図２】同例の機構部を示す断面図である。
【図３】同例の電位制御（ａ）及び（ｂ）のフローを示すフローチャートである。
【図４】同例の感光体ドラム及びパッチパターンを展開して示す図である。
【図５】同例における感光体ドラムの表面電位とトナー付着量との関係を示す特性図である。
【図６】同例の近似直線と制御電位との関係を示す図である。
【図７】同例のテ−ブルを示す図である。
【図８】同例の電位制御（ｂ）におけるトナー補給制御の説明図である。
【図９】同例の反射濃度センサの出力特性図である。
【符号の説明】
１０３ 感光体ドラム
１０８ 現像装置
２０１ メイン制御部
２０８ 光学方式反射濃度センサ
２１１ 表面電位センサ[0001]
BACKGROUND OF THE INVENTION
The present invention forms a latent image pattern on an image carrier in an image forming apparatus such as a copying machine, a facsimile machine, a printer, etc., measures development characteristics from the potential and toner adhesion amount, and uses the development characteristics at the time of image formation. The present invention relates to a potential control method in an image forming apparatus that determines various potentials.
[0002]
[Prior art]
In an electrophotographic image forming apparatus such as a copying machine, a facsimile machine, or a printer, an image carrier made up of a photosensitive drum or the like is generally rotated by a driving means such as a motor, and the image carrier is uniformly charged by a charging device. Then, an image is written on the image carrier by image exposure by an exposure device to form an electrostatic latent image, the electrostatic latent image is developed by a developing device, and then transferred to a transfer material by a transfer device. It is fixed on the transfer material.
[0003]
In such an electrophotographic image forming apparatus, an electrostatic latent image pattern is formed on the image carrier, the electrostatic latent image potential is measured, and the developed image is visualized by a developing device. There is known a method for obtaining development characteristics from the development characteristics and calculating various potentials such as a development bias potential and a charging potential of the image carrier from the development characteristics. For example, a potential control method for preparing various reference values of toner adhesion amounts in advance for the number of latent image patterns and determining various potentials by comparing these reference values with the toner adhesion amounts on the latent image patterns. There is (1). As another potential control method, the electrostatic latent image potential of the latent image pattern and the toner adhesion amount after the pattern is visualized are measured using respective measuring means. A method {circle around (2)} for obtaining development characteristics, a so-called linear approximation formula of development γ by linear approximation, setting the slope of the linear approximation formula as development efficiency, and obtaining various potentials from this development efficiency is presented.
[0004]
[Problems to be solved by the invention]
In the potential control method {circle around (1)}, it is difficult to correctly set the reference value. In particular, when a developer with large environmental fluctuations and fluctuations with time is used, the algorithm for controlling the various potentials is the environment of the developer. It becomes complicated in order to avoid the influence of fluctuation and fluctuation over time, and it takes a very long time to obtain a stable potential. In the potential control method {circle around (2)}, various potentials are determined only from the slope of the approximate linear equation. Therefore, it cannot be said that the accuracy is sufficient with respect to fluctuations in the developer and the image carrier. Tends to be unstable. In particular, when applied to a full-color copying machine that is susceptible to potential fluctuations, color fluctuations are likely to occur due to potential changes, and the stability of the highlight portion of a full-color image is particularly poor.
[0005]
In addition, a latent image pattern that has been visualized generally has a certain number (gradation), which is preferable in order to obtain development characteristics, but the toner consumption associated with the visualization of the latent image pattern. And a problem that it takes a long time to form a pattern occurs, so that it cannot be formed frequently.
For this reason, it was not possible to quickly cope with changes in development characteristics until the next pattern formation.
[0006]
The present invention improves the above-mentioned drawbacks, and can control the potential with high accuracy in a short time without increasing the toner consumption accompanying the visualization of the latent image pattern. An object is to provide a potential control method in an image forming apparatus that is optimal for reproduction, and a toner replenishment control method that is optimal for an image forming apparatus that employs this type of potential control method.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, after the image carrier is uniformly charged by charging by a charging device, an image is written by exposure by an exposure device to form an electrostatic latent image. A method for controlling the electric potential of the charging, the electric potential of the exposed portion subjected to the exposure, and the developing bias voltage used in the developing device in an image forming apparatus that develops the latent image with a developing device, characterized by the following: .
First, when starting up the image forming apparatus, The following first control is performed. That is, A plurality of latent image patterns having different potentials are formed on the image carrier, and the potentials are measured by a potential measuring unit. The latent image patterns are visualized by the developing device, and the toner adhesion amount is determined by the toner adhesion amount. The development γ characteristic line is obtained on the basis of the measurement result and the measurement result.
And The next second control is performed at a cycle shorter than the cycle for performing the first control. That is, Both of the above development γ characteristic lines Before reaching the point where the toner adhesion amount is large and exhibits saturation characteristics Straight line Manai A plurality of latent image patterns having different potentials selected on the basis of the measurement result at the start-up so that the total number is smaller than the total number of the plurality of latent image patterns formed at the start-up. The latent image pattern is visualized and the toner adhesion amount is measured by the toner adhesion amount measurement means. Based on the measurement results, the above charging device is used. A potential to be used, a potential to be used in the exposure apparatus, and a developing bias voltage are determined.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 2 is a schematic configuration diagram of an image forming apparatus to which the present invention can be applied.
This image forming apparatus is an example of an electrophotographic image forming apparatus composed of a full-color copying machine. The copying machine has a printer unit 101 and a color image reading device (hereinafter referred to as a color scanner) 102 which are electrophotographic color image recording devices. The color scanner 102 irradiates a document on a document placement table 119 made of contact glass with a light source 120 made of an exposure lamp, and reflects the reflected light image through an optical system made up of reflection mirrors 121 to 123 and an imaging lens 124. The image is imaged on the sensor 125 and the color image information of the original is separated into, for example, blue, green, and red, read, and converted into an electrical image signal. The color sensor 125 converts color image information of an original into color image separation means for color separation for each of blue, green, and red, for example, and converts image information of each color separated by the color separation means into an electrical image signal. It is composed of a photoelectric conversion element composed of a CCD and performs the same reading for three colors. The color separation image signals of blue, green, and red obtained by the color sensor 125 are subjected to color conversion processing by an image processing unit (not shown) based on the intensity level, and black (hereinafter referred to as BK), cyan. (Hereinafter referred to as C), magenta (hereinafter referred to as M), and yellow (hereinafter referred to as Y) color image data.
[0013]
The printer unit 101 forms visible images of BK, C, M, and Y from the color image data from the image processing unit to form a final color copy. Here, in the color scanner 102 for obtaining BK, C, M, and Y image data, the exposure lamp 120 and the optical systems 121 to 123 move to the left in accordance with the operation of the printer unit 102 and a predetermined timing. Thus, the original on the original table 119 is scanned, and one color image data is obtained for each original scan. When the color scanner 102 repeats such an operation four times in total, the image processing unit sequentially obtains image data of four colors BK, C, M, and Y. Each time image data of each color is obtained, the printer unit 102 sequentially forms a visible image with the image data and superimposes them to form a four-color full-color image.
[0014]
In the printer unit 101, the image carrier 103 made up of a photosensitive drum is stopped during non-image formation (copy standby). The photosensitive drum 103 is rotated by a main motor during image formation (copying) and is uniformly charged by a charging unit 104 including a charging charger, and then exposed to an exposure unit 105 including a laser optical system every rotation. The image exposure of each color component of black, cyan, magenta, and yellow is sequentially performed by the laser light irradiation, thereby forming an electrostatic latent image of each color component sequentially.
[0015]
The laser optical system 105 converts the color image data from the image processing unit into an optical signal and performs optical writing corresponding to the document image on the photosensitive drum 103 to form an electrostatic latent image. The laser optical system 105 includes a laser, a light emission drive control unit that performs light emission drive control, a polygon mirror, a motor that rotates the mirror, an f / θ lens, a reflection mirror, and the like. Driven by image data to emit light. The optical signal from this laser is deflected by a polygon mirror and applied to the photosensitive drum 103 via an f / θ lens and a reflection mirror.
[0016]
The photosensitive drum 103 rotates counterclockwise as indicated by an arrow in the figure. Around the photosensitive drum 103, a photosensitive member cleaning device 112, a charge eliminating lamp 113, a charging charger 104, a BK developing device 106, a C developing device 107, an M developing device 108, a Y developing device 109, an optical reflection density sensor. 208, an intermediate transfer belt 110, and the like are disposed. Each of the developing devices 106 to 109 includes developing sleeves 106 a, 107 a, 108 a, and 109 a that rotate while contacting the ears of the developer with the surface of the photosensitive drum 103 in order to develop the electrostatic latent image on the photosensitive drum 103. The developing paddles 106b, 107b, 108b, and 109b rotate to draw up and stir the internal developer, and toner density sensors 106c, 107c, 108c, and 109c that detect the toner density of the developer. In the standby state, all of the four developing devices 106 to 109 are in a state where the developer on the developing sleeves 106a, 107a, 108a, and 109a is in the state of cutting off (development inactive), and each developing operation of the developing devices 106 to 109 is performed. (The order of image formation of BK, C, M, and Y) is the order of developing the electrostatic latent images in the order of BK, C, M, and Y. However, the order of image formation for each color is not limited to this, and can be any order.
[0017]
At the start of the copying operation, the photosensitive drum 103 rotates and is uniformly charged by the charging charger 104. Then, the color scanner 102 starts reading for obtaining the BK image data at a predetermined timing, and the image processing unit obtains the BK image data from the image data from the color scanner 102, and the laser optical system based on the BK image data. The system 105 performs optical writing with a laser beam on the photosensitive drum 103 to form a latent image. Hereinafter, the electrostatic latent image based on the BK image data is referred to as a BK latent image. An electrostatic latent image based on C, M, and Y image data is also referred to as a C latent image, an M latent image, and a Y latent image. In order to develop this BK latent image from its leading end, the developing sleeve 106a starts rotating before the leading end of the latent image arrives at the developing position of the BK developing device 106, and the developer is spiked. Develop the latent image with BK toner. Thereafter, the developing operation of the BK latent image area on the photosensitive drum 103 is continued. When the trailing edge of the latent image passes the BK developing position, the BK developing position is quickly moved to the developer spike 106 on the developing sleeve 106a. Cut off to disable development. This is completed at least before the leading edge of the C latent image by the next C image data arrives. Note that the developer cutting is performed by switching the rotation direction of the developing sleeve 106a to the opposite direction to that during the developing operation. At this time, the other developing devices 107 to 109 remain in a development inoperative state.
[0018]
The BK toner image on the photosensitive drum 103 is transferred to the surface of the intermediate transfer belt 110 that is driven at the same speed as the photosensitive drum 103 (hereinafter, toner image transfer from the photosensitive drum 103 to the intermediate transfer belt 110). Is called belt transfer). The belt transfer is performed by applying a predetermined bias voltage to an electrode 111 including a transfer bias roller in contact with the intermediate transfer belt 110 in a state where the photosensitive drum 103 and the intermediate transfer belt 110 are in contact with each other. The photosensitive drum 103 is cleaned by the photosensitive member cleaning device 112 after the transfer of the BK toner image, is neutralized by the neutralizing lamp 113, and is uniformly charged again by the charging charger 104. The intermediate transfer belt 110 is a four-color superimposed belt transfer image obtained by sequentially aligning and transferring BK, C, M, and Y toner images sequentially formed on the photosensitive drum 103 on the same surface. After that, the belt transfer image is collectively transferred onto a transfer sheet as a transfer material as will be described later.
[0019]
By the way, the photosensitive drum 103 side proceeds to the C image forming process after the BK image forming process. In this C image forming process, the color scanner 103 starts reading for obtaining C image data at a predetermined timing. The image processing unit obtains C image data from the image data obtained from the image data, and based on the C image data, the laser optical system 105 performs optical writing on the photosensitive drum 103 with a laser beam to form a C latent image.
[0020]
The C developing device 107 starts rotation of the developing sleeve 107a after the previous trailing edge of the BK latent image has passed with respect to the developing position and before the leading edge of the C latent image arrives. And the C latent image is developed with C toner. Thereafter, the C developing device 107 continues to develop the C latent image area on the photosensitive drum 103. When the rear end portion of the C latent image passes, the C developing sleeve is the same as in the case of the previous BK developing device 106. The developer on 107a is trimmed. This is also completed before the next M latent image leading edge arrives.
[0021]
The C toner image on the photosensitive drum 103 is transferred to the surface of the intermediate transfer belt 110 that is driven at the same speed as the photosensitive drum 103. The photosensitive drum 110 is cleaned by the photosensitive member cleaning device 112 after the transfer of the C toner image, is neutralized by the neutralizing lamp 113, and is uniformly charged again by the charging charger 104.
[0022]
On the photosensitive drum 103 side, the process proceeds to the M image forming process after the C image forming process. In this M image forming process, the color scanner 103 starts reading for obtaining M image data at a predetermined timing. The image processing unit obtains M image data from the image data, and based on the M image data, the laser optical system 105 performs optical writing on the photosensitive drum 103 with laser light to form an M latent image.
[0023]
The M developing device 108 starts rotation of the developing sleeve 108a after the previous trailing edge of the C latent image has passed with respect to the developing position and before the leading edge of the M latent image has arrived. And developing the M latent image with M toner. Thereafter, the M developing device 108 continues to develop the M latent image area on the photosensitive drum 103, but when the rear end portion of the M latent image passes, the M visible image is the same as in the case of the previous C developing device 107. The developer on the sleeve 108a is trimmed. This is also completed before the next Y latent image leading edge arrives.
The M toner image on the photosensitive drum 103 is transferred to the surface of the intermediate transfer belt 110 that is driven at the same speed as the photosensitive drum 103. The photosensitive drum 103 is cleaned by the photosensitive member cleaning device 112 after the transfer of the M toner image, is neutralized by the neutralizing lamp 113, and is uniformly charged again by the charging charger 104.
[0024]
On the photosensitive drum 103 side, the process proceeds to the Y image forming process after the M image forming process. In this Y image forming process, the color scanner 102 starts reading to obtain Y image data at a predetermined timing. The image processing unit obtains Y image data from the image data, and based on the Y image data, the laser optical system 105 performs optical writing with the laser beam on the photosensitive drum 103 to form a Y latent image.
[0025]
The Y developing device 109 starts rotation of the developing sleeve 109a after the previous trailing edge of the M latent image has passed with respect to the developing position and before the leading edge of the Y latent image has arrived. The Y latent image is developed with Y toner. Thereafter, the development of the Y latent image area on the photosensitive drum 103 is continued at the Y developing position 109, but when the rear end of the Y latent image passes, the Y visible image is the same as in the case of the previous M developing device 108. The developer on the sleeve 109a is trimmed. This is also completed before the trailing edge of the Y latent image arrives. The Y toner image on the photosensitive drum 103 is transferred to the surface of the intermediate transfer belt 110 that is driven at the same speed as the photosensitive drum 103.
[0026]
Further, the intermediate transfer belt 110 is stretched around a drive roller 131, a belt transfer bias roller 111, and driven rollers 132 and 133, and a transfer bias voltage is applied from the power supply circuit via the belt transfer bias roller 111. The driving roller 131 is driven by the motor, and the intermediate transfer belt 110 rotates.
The belt cleaning device 115 includes a rubber blade, a contact / separation mechanism with respect to the intermediate transfer belt 110, and the like, when transferring the belt of the C image, the M image, and the Y image after transferring the BK image of the first color to the belt. The rubber blade is separated from the intermediate transfer belt 110 by the contact / separation mechanism.
[0027]
The paper transfer bias roller 114 is usually separated from the intermediate transfer belt 110, and the contact / separation mechanism takes timing when the four color superimposed images formed on the intermediate transfer belt 110 are collectively transferred onto the transfer paper. The intermediate transfer belt 110 is pressed against the intermediate transfer belt 110, and a predetermined bias voltage is applied to the paper transfer bias roller 114 from the power supply circuit to the transfer paper passing between the paper transfer bias roller 114 and the intermediate transfer belt 110. The superimposed image of four colors on 110 is transferred.
(The following margin)
[0028]
In this case, the transfer sheet is fed from a sheet feeding device 134 including a transfer sheet cassette to a registration roller 136 by a sheet feeding roller 135, and the registration roller 136 removes the transfer sheet from the leading end portion of the four-color superimposed image on the intermediate transfer belt 110. Is fed in accordance with the timing at which the paper reaches the paper transfer position.
[0029]
The transfer paper onto which the four-color superimposed toner images are collectively transferred from the intermediate transfer belt 110 is conveyed to a fixing device 117 by a conveying device including a conveying belt, and is fixed to a fixing roller 117a controlled to a predetermined temperature of the fixing device 117. The toner image is fixed by heating and pressurizing with the pressure roller 117 b and is carried out as a full color copy to the paper discharge tray 118.
Further, the surface of the photosensitive drum 103 after the belt transfer is cleaned by the photosensitive member cleaning device 112.
During repeat copying in which copying is performed continuously, the operation of the color scanner 102 and image formation on the photosensitive drum 103 are started following the first Y (fourth color) image forming process, and the second sheet is printed at a predetermined timing. The process proceeds to the BK (first color) imaging process.
In addition, the intermediate transfer belt 110 is cleaned by the cleaning device 115 following the process of transferring the four-color superimposed image to the first transfer sheet at a time, and the second BK toner image is transferred onto the belt there. The Thereafter, the same operation as that of the first sheet is performed, and thereafter the same operation is performed for each sheet.
[0030]
FIG. 1 shows a control system built in the copying machine.
This control system includes a main control unit 201 and a plurality of peripheral control units. The main control unit 201 temporarily stores various data as a main CPU 202, a ROM 203 storing a control program and various data, and a work area. The RAM 204 and an I / O interface unit 205 for performing input / output with each peripheral control unit and the like are configured.
[0031]
The main control unit 201 also includes a laser optical system control unit 206, a power supply circuit 207, a reflection density sensor 208, toner density sensors 106c, 107c, 108c, and 109c, an environmental sensor 210, and a surface potential sensor via an I / O interface unit 205. 211, a toner supply circuit 212, an intermediate transfer belt driving unit 213, and the like are connected. A laser optical system control unit 206 controls the laser optical system 105 based on an instruction from the main CPU 202, and a power supply circuit 207 applies a high voltage to the charging charger 104 based on an instruction from the main CPU 202 to transfer the transfer bias roller 111, paper transfer A transfer bias voltage is applied to the bias roller 114, and a developing bias potential is applied to the developing rollers 106a, 107a, 108a, and 109a, respectively. The reflection density sensor 208 optically detects the reflection density of the toner image on the photosensitive drum 103 between the yellow developing device 109 and the intermediate transfer belt 110, and the environment sensor 210 detects temperature and humidity. The surface potential sensor 211 detects the surface potential of the photosensitive drum 103 between the charging charger 104 and the black developing device 106.
[0032]
A toner replenishment circuit 212 replenishes magenta toner from the magenta toner replenishment unit to the magenta developing device 108 based on an instruction from the main CPU 202. Similarly, a plurality of toner replenishment circuits (not shown) each receive black toner based on an instruction from the main CPU 202. Black toner, cyan toner, and yellow toner are replenished from the replenishing unit, the cyan toner replenishing unit, and the yellow toner replenishing unit to the black developing device 106, the cyan developing device 107, and the yellow developing device 109. The intermediate transfer belt drive unit 213 drives the drive roller 131 based on an instruction from the CPU 202 to rotate the intermediate transfer belt 110.
[0033]
3A and 3B show a potential control routine of the main control unit 201. FIG.
Potential control by the potential control routine of this embodiment includes potential control a and potential control b. In the routine of potential control a of the main control unit 201, an input signal from a fixing temperature sensor that detects the fixing temperature of the fixing device 117 is received at step 501 in order to distinguish the power-on state from an abnormal process such as a jam. Based on this, it is determined whether or not the fixing temperature of the fixing device 117 exceeds 100 ° C., and if the fixing temperature of the fixing device 117 exceeds 100 ° C., it is determined as abnormal and the potential control a is not performed.
On the other hand, the potential control b is performed every time the image is formed.
In this embodiment, the potential control a is basically performed when the apparatus is activated. However, the potential control a may be performed every time a predetermined number of copies are made or every certain time as necessary.
[0034]
The potential control (a) will be described below.
When the fixing temperature of the fixing device 117 does not exceed 100 ° C., the main control unit 201 performs step 502. In the table Of the surface potential sensor 211 Comparison The calibration is performed positively and the calibration value is used in the subsequent potential calculation. Next, in the Vsg adjustment in step 503, the main control unit 201 takes in an output value for the background portion of the photosensitive drum 103 from the reflection density sensor 208 and irradiates the background portion of the photosensitive drum 103 from the reflection density sensor 208. The light emission amount of the reflection density sensor 208 is adjusted so that the reflected light of the light becomes a constant value.
[0035]
Next, the main control unit 201 forms a latent image pattern on the photosensitive drum 103 (step 504).
As shown in FIG. 4, electrostatic latent images (N electrostatic latent image patterns) 301, 302, 303... Having N gradation densities at the center in the width direction of the photosensitive drum 103 are photosensitive members. The rectangular latent image patterns 301, 302, 303,... Are formed at predetermined intervals along the rotation direction of the drum 103. In step 505, the output value of the surface potential sensor 211 with respect to the potential of these electrostatic latent images 301, 302, 303... Is read and stored in the RAM 204. Then, the main control unit 201 visualizes ten latent image patterns 301, 302, 303... On the photosensitive drum 103 in sequence at predetermined intervals for four colors of black, cyan, magenta, and yellow. Turn into.
[0036]
Next, in the P sensor detection in step 506, the main control unit 201 converts the latent image patterns 301, 302, 303... For four colors on the photosensitive drum 103 into the black developing device 106, cyan for each color. Each of the color toner images is developed by the developing device 107, the magenta developing device 108, and the yellow developing device 109 to be visualized, and the output value of the reflection density sensor 208 for each color toner image is Vpi (i = 1-N) is stored in the RAM 204.
[0037]
The main control unit 201 uniformly charges the photosensitive drum 103 to the charging charger 104 and changes the output of the laser optical system 105 via the laser optical system control unit 206 to change the latent image patterns 301, 302, 303,. However, the present invention is not limited to such a method, and the latent image pattern is visualized by switching the developing bias potential of each of the developing devices 106 to 109 without operating the laser optical system 105. You may make it image.
[0038]
Next, the main control unit 201 refers to the output value of the reflection density sensor 208 stored in the RAM 204 in the adhesion amount calculation step of step 507, referring to the table stored in the ROM 203, and determines the toner adhesion amount per unit area. Converted and stored in the RAM 204. Then, steps 508 to 510 are executed. Hereinafter, these steps will be described in detail.
[0039]
FIG. 5 is a plot of the relationship between the potential data obtained in step 505 and the toner adhesion amount data obtained in step 507 in each latent image pattern on the xy plane. The x axis indicates the potential (the difference between the developing bias potential VB and the surface potential VD of the photosensitive drum 103: VB−VD) (unit V), and the y axis indicates the toner adhesion amount per unit area (mg / cm). ² ). An infrared light reflection type sensor such as the optical reflection density sensor 208 of this embodiment is generally shown in FIG. 9 As shown in FIG. 5, the saturated adhesion characteristic is exhibited in the multi-adhesion portion where the toner adhesion amount is large, and the obtained detection value does not correspond to the actual toner adhesion amount.
For this reason, if the toner adhesion amount is calculated using the detection value of the reflection density sensor 208 obtained at the multiple adhesion portion as it is, an adhesion amount different from the actual adhesion amount is obtained, and this toner adhesion is obtained. The toner replenishment control based on the amount cannot be performed accurately.
In view of this, the main control unit 201 of the present embodiment determines the potential of the latent image pattern obtained from the surface potential sensor 211 and the reflection density sensor 208 for each latent image pattern of each color and the toner adhesion amount after visualization. As described later, the data is selected only in the linear section of the relationship (development γ characteristics of the developing device) between the potential data Xn (n = 1 to 10) and the toner adhesion amount data Yn. To do. Moreover, The data for this interval Do Development characteristics of each developing device 106-109 Of least squares Linear approximation by An approximate linear equation (E) of development characteristics is obtained for each color, and a control potential is calculated for each color by this approximate linear equation (E).
[0040]
The following formula is used for the calculation of the least square method.
Xave = ΣXn / k (1)
Yave = ΣYn / k (2)
Sx = Σ (Xn−Xave) * (Xn−Xave) (3)
Sy = Σ (Yn−Yave) * (Yn−Yave) (4)
Sxy = Σ (Xn−Xave) * (Yn−Yave) (5)
When the approximate linear equation (E) obtained from the potential of the latent image pattern obtained from the surface potential sensor 211 and the reflection density sensor 208 and the toner adhesion amount data after the visualization is Y = A1 * X + B1, the coefficient A1, B1 uses the above variables
A1 = Sxy / Sx (6)
B1 = Yave−A1 * Xave (7)
It can be expressed.
[0041]
The correlation coefficient R of the approximate linear equation (E) is
R * R = (Sxy * Sxy) / (Sx * Sy) (8)
It can be expressed as In this embodiment, the main control unit 201, in step 508, the potential data Xn of the latent image pattern obtained from the surface potential sensor 211 and the reflection density sensor 208 for each color, and the toner adhesion amount data after visualization. A group of five data (X1 to X5, Y1 to Y5), (X2 to X6, Y2 to Y6), (X3 to X7, Y3 to Y7), (X4 to X8, Y4 to Y8), (X5 to X9, Y5 to Y9), (X6 to X10, Y6 to Y10) are taken out and linear approximation calculation is performed in accordance with the above-described equations (1) to (8), and the correlation coefficient R is calculated. Thus, the following six sets of approximate linear equations and correlation coefficients (9) to (14) are obtained.
[0042]
Y11 = A11 * X + B11; R11 (9)
Y12 = A12 * X + B12; R12 (10)
Y13 = A13 * X + B13; R13 (11)
Y14 = A14 * X + B14; R14 (12)
Y15 = A15 * X + B15; R15 (13)
Y16 = A16 * X + B16; R16 (14)
The main control unit 201 selects, as the approximate linear equation (E), one set of approximate linear equations corresponding to the maximum value of the correlation coefficients R11 to R16 from the obtained six sets of approximate linear equations. .
[0043]
Next, in step 509, the main control unit 201 determines that the value of X when the Y value becomes the required maximum toner adhesion amount Mmax as shown in FIG. The value, that is, the value Vmax of the development potential is calculated. Each developing bias potential V of the black developing device 106, the cyan developing device 107, the magenta developing device 108, and the yellow developing device 109. _B And surface potential (exposure potential) V by image exposure of each color on the photosensitive drum 103 _L Is given by the following equations (15) and (16) from the above equation,
Vmax = (Mmax−B1) / A1 (15)
V _B -V _L = Vmax = (Mmax-B1) / A1 (16)
V _B And V _L Can be expressed by using the coefficient of the approximate linear method (E).
Therefore, equation (16) is
Mmax = A1 * Vmax + B1 (17)
It becomes.
[0044]
Here, the charging potential V before exposure of the photosensitive drum 103 _D And development bias potential V _B Is a linear equation as shown in FIG.
Y = A2 * X + B2 (18)
X-coordinate V of intersection of x axis _K From (development start voltage of the developing device) and the scumming margin voltage Vα obtained experimentally,
V _D -V _B = V _K + Vα (19)
Given in.
[0045]
Therefore, Vmax, V _D , V _B , V _L Is determined by equations (16) and (19). In this example, Vmax is used as a reference value and each control voltage V _D , V _B , V _L Is obtained in advance by experiments or the like, and is tabulated and stored in the ROM 203 as shown in FIG. In step 510, the main control unit 201 selects a table having Vmax closest to the calculated Vmax for each color, and each control voltage V corresponding to the selected table. _B , V _D , V _L Is the target potential.
[0046]
Next, in step 511, the main control unit 201 controls the laser emission power of the laser optical system 105 to be the maximum light amount via the laser optical system control unit 206, and takes in the output value of the surface potential sensor 211. Thus, the residual potential of the photosensitive drum 103 is detected. In step 512, when the residual potential is not 0, the target potential V determined by the above table is used. _B , V _D , V _L The residual potential is corrected for the target potential. Finally, in step 513, the power supply circuit 207 is adjusted so that the charging potential of the photosensitive drum 103 by the charging charger 104 becomes the target potential VD, and laser light emission in the laser optical system 105 is performed via the laser optical system control unit 206. The power is adjusted so that the exposure potential of the photosensitive drum 103 becomes the target potential VL, and the developing bias voltages of the black developing device 106, the cyan developing device 107, the magenta developing device 108, and the yellow developing device 109 are set as described above. The power supply circuit 207 is adjusted so as to be the target potential VB.
Next, this V _D , V _L The same residual potential is corrected for a predetermined number of potentials in a table centered on the target potential (two potentials obtained from the upper and lower tables centered on the target potential of interest in this embodiment), Use the final target potential. And V _D The charging charger grid voltage V applied to the charging charger 104 so as to achieve the target potential of _G To change V _D Is adjusted to the target potential. Next, V _D Is obtained, V _L Adjust the laser power to achieve the target potential. The charging charger grid voltage V obtained for a predetermined potential _G The laser power adjustment value is stored in the RAM 204. This value is used in the next potential control b. .
[0047]
Next, the potential control b of the main control unit 201, which is a feature of the present invention, will be described with reference to FIG.
In the latent image pattern formation in step 601, as in the above-described potential control a, as shown in FIG. 4, an electrostatic latent image pattern (N pieces of N latent image patterns having N gradation densities at the center in the width direction of the photosensitive drum 103 is formed. (Latent image patterns) 301, 302, 303... Are formed at predetermined intervals along the rotation direction of the photosensitive drum 103. In the potential control b of the present embodiment, rectangular latent image patterns 301, 302, and 303 having three different gradation densities each having a side of 40 mm are formed at intervals of 10 mm. The output value of the surface potential sensor 211 with respect to the potentials of the latent image patterns 301, 302, and 303 is read and stored in the RAM 204. The main control unit 201 visualizes the three latent image patterns 301, 302, and 303 on the photosensitive drum 103 sequentially at predetermined intervals for four colors of black, cyan, magenta, and yellow.
[0048]
What is important here is the potential (laser power) when the latent image pattern is formed. This potential is a latent value obtained by appropriately dividing the linear section determined from the upper and lower limits of the potential data and the toner adhesion amount data used when the approximate linear equation is obtained from the development characteristics (see FIG. 5) obtained by the potential control a. It is desirable to set the three potentials so as to form an image pattern, and this is a point for reducing the number of patches.
Here, if it is difficult to calculate the straight section, the target toner adhesion amount on the latent image pattern may be determined in advance by an experiment after a certain degree of accuracy reduction is recognized.
[0049]
Next, in P sensor detection (detection by the reflection density sensor 208) in step 603, the latent image patterns 301, 302, and 303 for the four colors on the photosensitive drum 103 are black developer 106 and cyan developed for each color. Each of the color toner images is developed by the device 107, the magenta developing device 108, and the yellow developing device 109 to be visualized, and the output value of the reflection density sensor 208 for each color toner image is Vpi (i = 1) for each color. ~ N) are stored in the RAM 204.
[0050]
Next, in the toner adhesion amount detection in step 604, the toner adhesion amount M / A (per unit area) by referring to the table stored in the ROM 203 for the output value of the reflection density sensor 208 stored in the RAM 204 in step 603. mg / cm ² ) And then stored in the RAM 204.
[0051]
FIG. 8 is a plot of data on each patch of the potential data obtained in step 602 and the adhesion amount data obtained in step 604 on the xy plane. The x-axis in FIG. 8 represents the potential potential, that is, the difference between the developing bias and the surface potential of the photosensitive drum 103: Vb−Vd (V), and the y-axis represents the toner adhesion amount M / A (mg per unit area). /cm ² ).
[0052]
In this potential control b, since the pattern data obtained from the surface potential sensor 211 and the reflection density sensor 208 are substantially in a straight section as shown in FIG. 8, the data in this section is compared with step 605. A linear equation is obtained, and from this, in step 606, the value of X at the required maximum toner adhesion amount Mmax, that is, the potential potential Vmax is calculated.
In the potential control b of the present embodiment, two points are selected from the three points, and the following three linear equations are obtained.
Y21 = A21 * X + B21 (20)
Y22 = A22 * X + B22 (21)
Y23 = A23 * X + B23 (22)
X = Vmax = (Mmax−B1) / A1 (15)
Note that the processing of the potential control b of this embodiment is performed from the standpoint of correcting the potential control a, and the value of Vmax obtained is not significantly different from the value of Vmax obtained by the processing of the potential control a. A straight line is selected so that Vmax obtained by the potential control b becomes a value closest to Vmax obtained by the potential control a. Thereby, for example, when a sudden change due to a temporary image detection error or the like occurs, it is possible to prevent Vmax from being obtained using the detection result at that time as it is.
[0053]
Here, in the potential control b of the present embodiment, two points are selected from three points to obtain a linear equation. However, the method is not limited to such a method, and an approximate straight line is obtained as described above. Of course, it is possible to increase the number of patterns. However, if the number is increased too much, a large amount of toner is consumed in addition to the original image formation. Therefore, it is desirable to obtain a linear equation with as little data as possible.
[0054]
Next, in step 607, Vmax is used as a reference value. _D , V _B , V _L 7 is stored in the ROM 203 in the form of a data table as shown in FIG. 7, and a table having Vmax closest to the calculated Vmax is selected for each color, and the control voltage V is determined based on the selected table. _B , V _D , V _L Is determined as a target potential.
[0055]
Next, in step 608, the target potential obtained in step 607 is set.
Here, unlike the potential control a, the potential control b is performed every time the image is formed. _D , V _L It is difficult in terms of time to perform feedback control so that becomes a target value. For this reason, V for the three tables obtained in the potential control a process in advance. _G , And a linear approximation of the relationship between the laser power adjustment values, the adjustment values are determined by calculation. .
[0056]
As described above, in the potential control method of the present invention, a plurality of latent image patterns having different toner adhesion amounts are formed on the photosensitive drum 103, the potentials are measured by the surface potential sensor 211, and the latent image patterns are visualized. The toner adhesion amount is measured by the reflection density sensor 208, and the development characteristics of the developing device at the start-up of the apparatus are calculated by the potential control a from the relationship between the measured potential and the toner adhesion amount. Further, in the potential control b, after the apparatus is activated, the development characteristics are calculated by reducing the number of the plurality of latent image patterns every time the image is formed.
Various potentials V for determining the development potential at the time of image formation of the image forming apparatus composed of a copying machine based on the development characteristics obtained by the potential control a and the potential control b. _B , V _D , V _L Since a smaller number of latent image patterns than the latent image pattern formed when calculating the potential control a are formed on the photosensitive drum 103, the potential control b has the same number of latent image patterns as the potential control a. Compared to the case of forming an image pattern, the pattern formation time can be shortened, and the toner consumption associated with the pattern formation can be reduced as much as possible to accurately grasp the development characteristics.
[0057]
In addition, the potential control b of the present embodiment is performed from the standpoint of correcting the potential control a, and a value closest to the value of Vmax obtained by the potential control a is employed. As a result, for example, even if a sudden change occurs in the detection result obtained by the potential control b due to a temporary image detection error or the like, erroneous potential control based on such a detection error or the like can be prevented. It is possible to accurately grasp the development characteristics and reproduce the optimum image from the obtained development characteristics.
[0058]
In particular, in the present embodiment, a plurality of sets of potential and toner adhesion amount data are obtained by the above measurement, and a section in which the relationship between the plurality of sets of potential and toner adhesion amount changes linearly is calculated. Since the approximate linear equation is obtained by linearly approximating the development characteristic from the data of the potential and the toner adhesion amount, and this approximate linear equation is used as the development characteristic, the detection characteristic of the reflection density sensor 208 is non-linear with a simple configuration. Even if it has, it is possible to perform accurate potential control without being affected by this non-linearity, and it is optimal for image reproduction against fluctuations in developer.
[0059]
Further, the approximate linear equation in the linear portion of the development characteristic is set as Y = A * X + B with A and B as coefficients, the measured potential data is X, the toner adhesion amount data is Y, and the developing bias potential V of the developing device. _B , Exposure potential V of the photosensitive drum 103 _L And the potential Vmax at which the maximum toner adhesion amount Mmax is obtained by potential control.
Mmax = A * Vmax + B
V _B -V _L = Vmax
Therefore, the developing bias potential V _B , Exposure potential V of the photosensitive drum 103 _L Can be accurately controlled.
[0060]
Further, K straight lines obtained by applying the least square method to M (M ≦ N) sets of data from the N sets of potential and toner adhesion amounts obtained in the above measurement. Thus, the correlation coefficient of each straight line is calculated, and the section of the combination of data from which the maximum value of the correlation function is obtained is set as the section, so that more accurate potential control can be performed.
[0061]
Next, it is optimal to employ the image forming apparatus that employs the potential control method that calculates the development characteristics of the developing device and determines various potentials during image formation of the image forming device, as in the above-described potential control method. An embodiment of the invention relating to a toner replenishment control method will be described.
In the potential control method according to the above-described embodiment, a plurality of latent image patterns having different toner adhesion amounts are formed, and the potentials of the latent image patterns and the toner adhesion amounts after the visualization are measured. Based on the relationship between the potential and the toner adhesion amount data, the actual (at that time) developing device development characteristics are calculated. Based on the calculated development characteristics, the power supply circuit 207 of the charging charger 104 and the laser of the laser optical system 105 are used so that a desired maximum toner adhesion amount Mmax can be obtained and a desired background contamination margin voltage can be secured. The light emission power, the developing bias potential of each developing device, and the like are adjusted, and control is performed so as to determine various potentials during image formation.
This development characteristic also reflects the influence of fluctuations in the developer, for example, fluctuations in the charge amount (Q / M) of the developer (carrier and toner), so that the developer is approaching the end of its life, for example. Even when the charge amount of the developer decreases, a desired maximum toner adhesion amount Mmax can be obtained, and a good image that can secure a desired background contamination margin voltage can be formed.
[0062]
For example, taking the amount of toner adhesion on the photosensitive drum 103 on the vertical axis and the potential on the photosensitive drum 103 on the horizontal axis, respectively, the approximate linear equation Y = A1 * obtained at the time of the first patch pattern formation is taken. The development characteristics change with time so that X + B1, the second approximate linear equation is Y = A2 * X + B2, and the third approximate linear equation is Y = A3 * X + B3. When the developer approaches the end of its life, the amount of charge of the developer decreases, and as a result, for example, the slope of the approximate linear equation gradually increases. Along with this, V can be obtained in accordance with an approximate linear equation corresponding to the calculated development characteristic so that a desired maximum toner adhesion amount Mmax can be obtained and a desired background contamination margin voltage can be secured. _D , V _B , V _L Therefore, for example, a desired image can be formed even under development characteristics in which the slope of the approximate linear equation is large.
[0063]
However, as a toner replenishment control method in an image forming apparatus that employs such a potential control method, there is a risk that a problem may occur if a conventionally known toner replenishment control method using a latent image pattern after visualization is used in combination. .
That is, in a conventionally known toner replenishment control method using a latent image pattern, a latent image pattern for toner adhesion amount detection is formed on the photosensitive drum 103, and the toner image is attached when this pattern is visualized. The toner replenishment amount is controlled by determining the toner adhesion amount based on the reflection density. The potential for forming this latent image pattern (the difference between the patch potential on the photosensitive drum 103 and the developing bias potential) is always kept constant. For this reason, as described above, the developer is approaching the end of its life, the charge amount (Q / M) of both the toner and the carrier is decreased, and the development characteristics are changed so that the slope of the approximate linear equation is increased. In this case, even if the toner density of the actual developer becomes considerably low, a certain amount of toner adhesion can be obtained on the latent image pattern after visualization. Therefore, the amount of toner replenished in accordance with the reflection density of the pattern after the visualization is reduced instead of the actual toner density, and the toner density is further lowered. As a result, the amount of toner adhering to the carrier is reduced, and the carrier is transferred to the photoconductive drum 103 side by direct contact with the surface of the photoconductive drum 103, causing problems such as carrier adhesion.
[0064]
Accordingly, in the toner replenishment control method of the present embodiment, the toner replenishment condition is determined in accordance with the development characteristics calculated in the potential controls a and b, thereby preventing a problem in toner replenishment control due to a change in the developer. Like to do. Hereinafter, the toner replenishment control method of this embodiment applied to the image forming apparatus employing the potential control method shown in FIGS. 3A and 3B will be described.
[0065]
When the image forming operation is started, a latent image pattern for potential control b is applied to a non-image area at a predetermined interval from the rear end of the image on the photosensitive drum 103 according to a predetermined image forming condition every time after image formation. The surface potential Vp of the latent image pattern portion is measured by the surface potential sensor 211, and the development bias is applied during the development of the latent image pattern so that the development potential of the latent image pattern becomes constant based on the measurement result of Vp. Apply. Then, the reflection density sensor 208 measures the reference reflection density Vsg of the background portion of the photosensitive drum 103 and the reflection density Vsp of the detection pattern portion. The reference reflection density Vsg of the background portion is adjusted in a state where there is no toner on the photosensitive drum 103 (in the present embodiment, about 4 V) when the potential control a is executed.
The toner supply is performed based on the measurement result of the latent image pattern used for the potential control b.
FIG. 9 is an example of output characteristics of the reflection density sensor 208 applied to the apparatus of this embodiment. A characteristic line a indicates black toner, and a characteristic line b indicates color toner. The output characteristics of the reflection density sensor 208 are such that the developing power (toner density) is low and the amount of reflected light increases when the toner adhesion amount on the pattern after visualization is small, and the output of the sensor 208, that is, the value of Vsp increases. To do. On the contrary, when the developing ability is high and the amount of toner adhering on the visualized pattern is large, the amount of reflected light decreases and the value of Vsp also decreases. However, in the case of the color toner indicated by the characteristic line b, when the toner adhesion amount exceeds a predetermined value, the reflected light from the toner surface increases and gradually increases again.
[0066]
Therefore, a preferable control level, that is, a prescribed value of the toner adhesion amount is roughly determined according to the output characteristics of the reflection density sensor 208, and in this embodiment, the prescribed value of the black toner adhesion amount is 0.4 mg / cm. ² The specified value of color toner adhesion amount is 0.3 mg / cm ² It is said.
For this reason, the black toner adhesion amount is 0.4 mg / cm 2 based on the development characteristics obtained by the potential control a. ² , Color toner adhesion amount 0.3mg / cm ² The latent image pattern of the developing potential is included in one of the latent image patterns of the potential control b.
For example, in the case of black toner, when the development characteristics obtained by the potential control a are as shown in FIG. 5, the development potential of the latent image pattern at three points when the determination of the linear region and the toner adhesion amount reach the above specified values. To decide.
Black toner: V _0.4 = (0.4-B1) / A1
Color toner: V _0.3 = (0.3-B1) / A1
If, for example, the toner adhesion amount is determined at three points of the specified values (0.3, 0.4, 0.5), the three development potentials at which such adhesion amount is obtained are controlled by the potential control a. It is 79,110,142 (V) when it calculates | requires by the approximate linear equation used by the process of (4).
The specified value is not limited to the three points (0.3, 0.4, 0.5), and may be determined according to the following criteria.
That is, the sensitivity characteristic of the reflection density sensor 208 is in a range showing linearity, and includes a prescribed value of the black toner adhesion amount and a prescribed value of the color toner adhesion amount for determining the developing potential, and more preferably 3 What is necessary is just to determine so that a point may become M / A at equal intervals.
[0067]
In the present embodiment, following the replenishment potential calculation, the Vb determined here is applied to the developing sleeve to develop the patch pattern. Reflected light with respect to the toner image on the developed patch pattern is detected by the reflection density sensor 208, and this potential is set to Vsp. The amount of reflected light in the toner non-development area is obtained in advance as Vsg, and the toner replenishment amount is determined based on the ratio of Vsp and Vsg.
Toner replenishment control is 0.4mg / cm for black toner ² (0.3 mg / cm for color toner ² The toner is replenished based on the output of the reflection density sensor 208 when the latent image pattern when the developing potential is 110 (V) is visualized. The replenishment amount at this time is obtained as follows by referring to the data table stored in the ROM 203 based on the output of the reflection density sensor 208.

The actual toner replenishment time X (sec) is Tadd (mg) as the calculated toner replenishment amount and K (mg / sec) as the replenishment capability of the toner replenishment motor.
X = Tadd / K
And Tona 1 to 3 under the above conditions correspond to the obtained toner replenishment amount Tadd.
[0068]
As a result, the pattern density after visualization, which is used for toner replenishment, is maintained within the range that the toner replenishment follows. However, because the developing ability may differ even with the same toner density due to environmental fluctuations over time, the toner gradually It is conceivable that the concentration rises or falls outside the preferred concentration range (for example, 4 to 7 wt%).
[0069]
In general, the slope of the development characteristic line increases as the toner concentration increases, and decreases as the absolute humidity decreases.
[0070]
Therefore, in the present invention, in consideration of this property, the slope of the development characteristic line is large from the development characteristics and the environmental characteristics so that the toner density is in a predetermined range. Preferably, the toner density is low when the absolute humidity is low. The development potential of the latent image pattern used for toner replenishment control is changed so that the toner density increases when the slope of the development characteristic line is small and the absolute humidity is high.
For example, as a result of the potential control a, when the slope of the development characteristic line is large, and desirably it is determined that the absolute humidity is low, 0.4 mg of the potential control b is set according to the degree so that the toner density decreases. Increase the development potential of the target latent image pattern by several tens of volts. As a result, the toner adhesion amount on the latent image pattern increases, so that the toner replenishment amount is suppressed and the toner density decreases.
[0071]
If the reflection density sensor 208 has the same sensitivity from the low adhesion amount region to the high adhesion amount region of the toner, the toner concentration, based on the detected value, even if no humidity sensor is provided. Image density can be controlled. However, in general, the reflection density sensor has low sensitivity in the high toner adhesion amount region, and therefore, based on the detection value detected in the medium adhesion amount region, the adhesion amount in the high adhesion amount region is predicted. Yes. Also, environmental fluctuations such as temperature and humidity, especially large fluctuations, affect the toner charge amount (Q / M), and the toner adhesion amount in the patch pattern will fluctuate, making this prediction difficult. Become. For this reason, it is desirable to use a sensor capable of detecting environmental fluctuations, such as a humidity sensor, in order to detect the toner adhesion amount in consideration of the absolute humidity condition, and is advantageous for controlling the toner density and the image density. There are many cases.
[0072]
Here, when the environmental change cannot be detected because the sensor for detecting the environmental change is not provided, the inclination of the development characteristic line based on the result of the potential control a, that is, the number of the selected potential control table, Similarly, when the slope of the development characteristic line is larger or smaller than the predetermined slope, the development potential of the latent image pattern used for the toner replenishment control of the potential control b is similarly set when the slope of the development characteristic line is large. If it is large or small, reduce it. According to this, although the toner density fluctuation amount is slightly increased as compared with the case where environmental fluctuations can be taken into consideration, it can be suppressed to a certain toner density range.
[0073]
As described above, according to the toner replenishment control method of the present embodiment, when such control is normally performed, if the toner density changes until the next development characteristic measurement only with the potential control a, the image also changes. On the other hand, since each potential is controlled by the potential control b in which the potential control is performed every time the image is formed, a stable image can be obtained following a short range change such as a toner density change.
[0074]
In particular, in the toner replenishment control method of the present embodiment, the development characteristics are directly detected in the apparatus, so that an optimum image potential can be obtained and an optimum toner density control condition can be determined. Thereby, the best image at that time can be guaranteed.
Further, since the development characteristic is used as the development characteristic using the linear equation in the region where the relationship between the latent image potential on the photosensitive drum 103 and the toner adhesion amount shows the linear characteristic, the stability of calculation accuracy can be obtained. In addition, the control routine can be simply constructed.
Further, since the reflection density sensor 208 for detecting the toner adhesion amount on the photosensitive drum 103 can be used for both the calculation of the development characteristics and the toner supply, the number of sensors can be minimized. . This simplifies the configuration and is very advantageous in terms of cost. In particular, when a full color system is constructed, it is not necessary to provide a sensor for toner density control for each color of toner density control, which is very advantageous.
[0075]
In the toner replenishment control method of the present embodiment, the development bias at the time of latent image pattern formation is assumed to be the case of black toner on the assumption of the calculated development characteristics (which are affected by fluctuations in developer characteristics). 0.4mg / cm ² In case of color toner, 0.3mg / cm ² Therefore, the toner adhesion amount to a certain level is obtained even when the toner density approaches the lower limit of the allowable range. For this reason, the amount of toner replenishment decreases instead of the actual toner concentration, and the toner concentration may be excessively lowered. However, such a fear can be referred to various known techniques for securing an optimum toner replenishment amount, for example, predicting the toner consumption amount using image data, and setting the predicted toner consumption amount when setting the toner replenishment amount. It can be eliminated by using the technique to do together. Of course, such a technique is also employed in the apparatus of the present embodiment.
(Hereinafter, blank space)
[0076]
【The invention's effect】
According to invention of Claim 1, In the second control that is performed in a cycle shorter than the cycle in which the first control is performed The total number of latent image patterns to be formed is In the first control performed at startup Since it is smaller than the total number of latent image patterns to be formed, In the first control Compared with the case where the same number of patterns as the number of latent image patterns to be formed are formed, the pattern formation time can be shortened, and toner consumption accompanying pattern visualization can be reduced. Moreover, since the latent image patterns within the linear section of the development γ characteristic line obtained at the start are used, the number of latent image patterns is smaller than that at the start. The Instead of forming, the development characteristics can be accurately grasped.
Therefore, various potential controls can be performed with high accuracy, and it is optimal for image reproduction against changes in the developer.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus to which the present invention can be applied.
FIG. 2 is a cross-sectional view showing a mechanism portion of the example.
FIG. 3 is a flowchart showing a flow of potential control (a) and (b) of the example.
FIG. 4 is a developed view showing a photosensitive drum and a patch pattern of the same example.
FIG. 5 is a characteristic diagram showing the relationship between the surface potential of the photosensitive drum and the toner adhesion amount in the example.
FIG. 6 is a diagram illustrating a relationship between an approximate line and a control potential in the example.
FIG. 7 is a diagram showing a table of the example.
FIG. 8 is an explanatory diagram of toner supply control in potential control (b) of the example.
FIG. 9 is an output characteristic diagram of the reflection density sensor of the same example.
[Explanation of symbols]
103 Photosensitive drum
108 Developing device
201 Main control unit
208 Optical reflection density sensor
211 Surface potential sensor

Claims (1)

After the image carrier is uniformly charged by charging by a charging device, an image is written by exposure by an exposure device to form an electrostatic latent image, and this electrostatic latent image is developed by a developing device. A method for controlling a potential, a potential of an exposed portion subjected to the exposure, and a developing bias voltage used in the developing device, characterized by the following.
First, the following first control is performed when the image forming apparatus is activated . That is, a plurality of latent image patterns having different potentials are formed on the image carrier, the potentials are measured by a potential measuring unit, and the latent image patterns are visualized by the developing device, and the toner adhesion amount is determined by toner. The development γ characteristic line is obtained based on the measurement results by the adhesion amount measuring means.
Then, the next second control is performed at a cycle shorter than the cycle for performing the first control. That is, either no less the total number than the total number of the plurality of latent image patterns formed at the start it was before linear ku while leading to the location of the toner adhesion amount is large saturation characteristics of the development γ characteristic line As described above, a plurality of latent image patterns with different potentials selected based on the measurement results at the time of starting are formed on the image carrier, and the potentials are measured by the potential measuring means and the latent image patterns are visualized. The toner adhesion amount is measured by the toner adhesion amount measuring means, and the potential used in the charging device, the potential used in the exposure device, and the developing bias voltage are determined based on the measurement results.

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