JP3882453B2 - Image forming apparatus - Google Patents

Description

【００５５】
【表２】

【００５６】
表１及び表２の結果から明らかなように、空検知からシャットダウンまでの間に相当するトナー濃度値（５％、４％）にあるとき、平常時のコントラスト電位（３５０Ｖ）である場合には、特に像中ＢＣＯが発生するが、そのコントラスト電位を小さくした場合（３００Ｖ、２５０Ｖ）には、像中ＢＣＯが発生しなくなることがわかる。また、この空検知からシャットダウンまでの間における像中ＢＣＯの発生は、表２の低湿環境下よりも表１の高湿環境下で発生しやすいこともわかる。ちなみに、低湿環境下において、表２に示すようにコントラスト電位を「４００Ｖ」にした場合には、像中ＢＣＯが発生しやすくなることがわかる。
【００５７】
［他の実施の形態］
実施の形態１では、潜像電位のプレ調整について、その潜像電位の可変最大値：Ｖ_L1をトナー濃度（ＴＣ）の低下に正比例させて徐々に小さい値となるように変更させることにより、コントラスト電位：Ｖ_contを徐々に小さくするような制御（図１）を行う場合を示したが、本発明では、図１１に例示するように、その潜像電位の可変最大値をトナー濃度の低下に対応させて段階的に小さい値となるように変更し、そのときのコントラスト電位：Ｖ_contも段階的に小さくなるような制御を行うようにしてもよい。この場合、そのコントラスト電位を段階的に小さくする割合については適宜設定すればよく、例えば、図１１に例示するように、トナー濃度ＴＣが「０．５％低下する」ごとにコントラスト電位：Ｖ_contを「１０Ｖ」ずつ小さくなるように設定することができる。
【００５８】
このように構成した場合にも、実施の形態１の場合と同様に、そのときのコントラスト電位が段階的に少しずつ小さな値になるため、空検知からシャットダウンまでの間における画像形成において画像濃度の急激な変動が発生することがなく、画質良好な画像形成が可能となる。
【００５９】
また、実施の形態１では、空検知からシャットダウンになるまでの間におけるコントラスト電位：Ｖ_contを小さくする手法として、潜像電位の可変最大値：Ｖ_Lを小さくする構成を採用した場合について例示したが、本発明では、図１２に例示するように、帯電電位：Ｖ_H及び現像バイアス：Ｖ_Dの電位を適宜変更する制御を行うようにしてもよい。この場合、帯電電位：Ｖ_H及び現像バイアス：Ｖ_Dの電位は、その帯電電位と現像バイアスの電位差：Ｖ_cln1が背景かぶりの発生しにくい電圧値に保たれるように同量だけ変更することが好ましい。例えば、図１２に例示するように、帯電電位については平常時の−７００Ｖを−６５０に変更し、現像バイアスについては平常時−５６０Ｖから−５００Ｖに変更することができる。
【００６０】
このように構成した場合にも、空検知からシャットダウンになるまでの間においては、平常時におけるコントラスト電位：Ｖ_cont1(３１０Ｖ)が２５０Ｖに変更されて小さくなる。これにより、その間においては、実施の形態１の場合と同様に、像中ＢＣＯと背景部かぶりの双方が発生しない画質良好な画像形成が可能となる。なお、この場合、潜像電位の可変最大値：Ｖ_Lについては、上記コントラスト電位が小さくなることを妨げない範囲であれば、必要な量だけ変更しても構わない。
【００６１】
また、このように構成した場合、帯電電位については変更せず、現像バイアスのみを上記のような条件下で変更したときには、背景部かぶりが更に発生しにくくなる一方で、電荷の注入により逆極性に帯電したキャリアが感光ドラム上の静電潜像以外の部分（背景部）に付着するという不具合が発生するようになるため適当ではない。
【００６２】
【発明の効果】
以上説明したように、本発明の画像形成装置によれば、トナー濃度センサを用いてトナー収容器の空検知をするタイプの画像形成装置であっても、特に空検知をしてから画像形成動作が強制終了されるまでの間における背景部かぶり及び像中ＢＣＯの発生を簡易かつ確実に防止することができる。特に、像中ＢＣＯを確実に防止できるため、像中ＢＣＯに起因した画像中の白抜けや筋等の発生をも回避することが可能になる。
【図面の簡単な説明】
【図１】 実施の形態１における制御内容によるトナー濃度とコントラスト電位との関係を示す相関図。
【図２】 実施の形態１に係るカラープリンタを示す概要図。
【図３】 現像装置の概略縦断面図。
【図４】 現像装置の概略横断面図。
【図５】 現像装置とトナー補給装置を示す斜視図。
【図６】 トナー濃度センサ等の検出情報を使用する制御系の構成を示すブロック図。
【図７】 トナー濃度（磁気）センサの出力特性図。
【図８】 図６の制御系による主な制御内容を示すフローチャート。
【図９】 プリント量に対するトナー濃度の推移と制御事項との関係を示す説明図。
【図１０】 実施の形態１における制御内容を示すもので、（ａ）は平常時における各電位状態を示す説明図、（ｂ）は空検知からシャットダウンになるまでの間における各電位状態を示す説明図。
【図１１】 他の実施形態における制御内容によるトナー濃度とコントラスト電位との関係を示す相関図。
【図１２】 他の実施形態における制御内容を示すもので、（ａ）は平常時における各電位状態を示す説明図、（ｂ）は空検知からシャットダウンになるまでの間における各電位状態を示す説明図。
【図１３】 従来技術の制御内容を示すもので、（ａ）は平常時における各電位状態を示す説明図、（ｂ）はトナー残量が少ないと判断されかつ印字動作を停止する前における各電位状態を示す説明図。
【符号の説明】
１１…感光ドラム（像担持体）、１３…ＲＯＳ（潜像形成装置）、１４…現像装置、１９…トナーカートリッジ（トナー収容器）、６０…磁気センサ（トナー濃度センサ）、７０…トナー補給装置、８０…制御装置（制御手段）、Ｖ_H…帯電電位、Ｖ_D…現像バイアス、Ｖ_L…潜像電位、Ｖ_cont1…平常時におけるコントラスト電位（潜像電位と現像バイアスとの電位差）、Ｖ_cont2…変更後におけるコントラスト電位、Ｇ…二成分現像剤。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus represented by a copying machine, a printer and the like using a two-component development system.
[0002]
[Prior art]
In an image forming apparatus such as a copying machine or a printer using a two-component development method, an electrostatic latent image formed on an image carrier such as a photosensitive drum according to image information is converted into a two-component developer composed of toner and a carrier. As a result of the development, the toner in the developer in the developing device containing the two-component developer is gradually consumed, and the toner concentration (mixing ratio: the mixing ratio of the toner with respect to the whole developer) decreases.
[0003]
Therefore, normally, the toner concentration of the two-component developer contained in the developing device is detected by a toner concentration sensor, and the toner replenishing device is replenished to the developing device so that the toner concentration is kept constant. The toner amount is controlled.
[0004]
In addition, in such an image forming apparatus using the toner concentration sensor, the toner container (toner cartridge) in the toner replenishing device uses the detection information from the toner concentration sensor to be in an empty state without toner. Control that causes the image forming operation to be forcibly terminated when it is determined that the toner remaining in the developing device has decreased after the determination (so-called “empty detection”). There is something to do.
[0005]
[Problems to be solved by the invention]
By the way, an image forming apparatus of the type that uses this toner density sensor to detect empty toner container has the following problems.
[0006]
That is, when the empty state is detected and the image forming operation is forcibly terminated, no new toner is supplied to the developing device, and the two-component developer contained in the developing device is not replenished. Since the remaining amount of toner also decreases approximately in proportion to the amount of the developing operation, the density of an image (toner image) obtained by developing with such a developing device tends to gradually decrease.
[0007]
Incidentally, Japanese Patent Application Laid-Open No. 5-53424 discloses an image forming apparatus that detects a toner remaining amount in a developing device with a (magnetic) sensor after detecting that the toner remaining amount in the developing device is low. A means for keeping the image density constant by appropriately changing the developing bias when the printing operation is stopped is shown. Specifically, when the amount of remaining toner is low, the developing bias is changed to a value that is a low value (potential on the side where the density is high).
[0008]
However, in the image forming apparatus disclosed in this publication, as shown in FIG. 13, before and after the change of the developing bias (FIG. A) and after the change (FIG. B), the image carrier after the change is changed. Charging potential V _H And development bias V _D Potential difference V _cln However, since the potential difference is smaller than the potential difference before the change by the change in the developing bias, there is a problem that so-called background fogging easily occurs, in which toner adheres to the non-image area. Moreover, the lower the developing bias when the toner density is, the lower the latent image potential V after the change. _L And development bias V _D Difference in potential V _cont Is larger than the potential difference before the change by an amount corresponding to the change in the developing bias.For example, the charge on the image carrier side is injected into the carrier, and the carrier itself is developed with a reverse polarity, so that the latent image portion of the image carrier is developed. There is a problem that the so-called BCO (bead carrier over) in the image is easily generated because the carrier is attracted to the image and attracted.
[0009]
In particular, when the BCO occurs in the image, the toner at the time of development does not adhere to the image area where the carrier adheres, so that white spots appear in the image, and the carrier of the image carrier is caused by the carrier. Since the surface is damaged, streaks and the like are generated in the image, which causes a problem more serious than the above-described problem of a decrease in image density. Further, the BCO in the image tends to be more likely to be generated in a high humidity environment than in a low humidity environment.
[0010]
The present invention has been made in view of the above-described circumstances, and an object of the present invention is, in particular, as an image forming apparatus of a type that performs empty detection of a toner container using a toner concentration sensor. Another object of the present invention is to provide an image forming apparatus capable of easily and reliably preventing the occurrence of background fogging and BCO in an image after the image forming operation is forcibly terminated.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus of the present invention includes an image carrier charged to a predetermined charging potential, and an electrostatic latent image having a predetermined latent image potential corresponding to image information on the image carrier. A latent image forming apparatus that forms a latent image, and a developing apparatus that develops an electrostatic latent image formed by the latent image forming apparatus in a state where a two-component developer composed of toner and a carrier is supplied and a developing bias is applied. A toner replenishing device for replenishing toner from the toner container in the developing device, a toner concentration sensor for detecting the toner concentration in the two-component developer accommodated in the developing device, and a toner concentration sensor Based on the detection information, at least the toner replenishing device is controlled, and based on the detection information, it is determined that the toner container is empty. After the determination, the remaining amount of toner in the developing device is low. In the image forming apparatus and a control means for performing control to abort the image forming operation when it is determined that Tsu,
The control means determines that the potential difference between the latent image potential and the developing bias is normal when the toner container is empty and after the image forming operation is forcibly terminated. The variable maximum value determined by the latent image forming apparatus of the latent image potential is changed to a value smaller than the variable maximum value in normal time so as to be a smaller value.
[0012]
Here, the term “normal” means that the developer is sufficiently contained in both the developing device and the toner container, and the toner concentration of the developer in the developing device is substantially maintained at a preset specified value. This is the time when the control of the toner supply device by the control means is being executed. As for the change amount of the variable maximum value of the latent image potential by the control means, the potential difference between the latent image potential and the developing bias is maintained in a potential region where BCO in the image is unlikely to occur, and an appropriate density gradation is ensured. For example, the variable maximum value of the latent image potential from when it is determined that the toner container is empty until the image forming operation is forcibly terminated is equal to the potential difference in normal times. It is good to set so that it may become a small value of about 0.75 times to 0.95 times. Incidentally, at the time of changing control of the variable maximum value of the latent image potential by the control means, the charging potential and the developing bias are fixed without being changed in principle.
[0013]
According to such an image forming apparatus, when the control unit determines that the toner container is empty (empty detection) and the image forming operation is forcibly terminated, the latent image is displayed. Control is performed to change the variable maximum value of the potential to a value smaller than the variable maximum value in normal times. As a result, the potential difference between the latent image potential and the developing bias is kept smaller than the potential difference in normal times. It comes to be. At this time, the charging potential and the developing bias are not particularly changed. As a result, the potential difference between the latent image potential and the developing bias does not become larger than the potential difference in normal times, but rather becomes a small value, so that the BCO in the image as in the prior art does not occur. In addition, since the potential difference between the charging potential of the image carrier and the developing bias is not reduced by changing the developing bias, the background fogging as in the prior art does not occur.
[0014]
Further, with respect to the control means, from a predetermined time before determining that the toner container is empty, the variable maximum value of the latent image potential is changed to the small variable maximum value to be changed after the determination. It is good to comprise so that it may change so that it may approach gradually or in steps. In this case, the predetermined time before the determination is appropriately set between a specified value of the toner density at normal time and a toner density value which is a reference for determining that the toner container is empty.
[0015]
In such a configuration, the variable maximum value of the latent image potential is gradually or stepwise reduced from a predetermined time before the control unit determines that the toner container is empty. Therefore, the potential difference between the latent image potential and the developing bias at that time also becomes a small value gradually or stepwise. As a result, there is no problem that the concentration or the like fluctuates abruptly as the potential difference is suddenly changed when the sky is detected.
[0016]
In addition, the image forming apparatus of the present invention for achieving the above object replaces the control by the control unit to change the variable maximum value of the latent image potential to a value smaller than the variable maximum value in normal times. And controlling the charging potential and the developing bias potential so that the potential difference between the latent image potential and the developing bias is smaller than the potential difference in normal times while keeping the potential difference between the two at a predetermined value. It is configured to do.
[0017]
Here, the predetermined value in the potential difference between the charging potential and the developing bias means a potential difference in which at least background portion fog is unlikely to occur. Further, it is preferable to change the charging potential and the developing bias by the control means by the same amount, but the same amount is not necessary as long as the predetermined value is ensured. Further, even in the case of the above configuration, the charging potential and the developing bias potential are kept at a predetermined value from a predetermined time before it is determined that the toner container is empty. However, it is preferable that the control is performed so that the small value to be changed after the determination is gradually or stepwise approached.
[0018]
According to such an image forming apparatus, when it is between when it is determined that the toner container is empty and when the image forming operation is forcibly terminated, the charging potential and the developing bias potential are both set. Control is performed such that the potential difference between the latent image potential and the developing bias is changed to a value smaller than the potential difference in normal times while maintaining the potential difference at a predetermined value. As a result, as in the case of the image forming apparatus, the potential difference between the latent image potential and the developing bias is maintained at a value smaller than the potential difference in the normal state. Will not occur.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
FIG. 2 shows a color printer as an image forming apparatus according to Embodiment 1 of the present invention.
[0020]
The color printer according to the first embodiment includes yellow (Y) and magenta (M) that are individually formed by four image forming units 10Y, 10M, 10C, and 10K based on image information input from an external connection device (not shown). , Cyan (C) and black (K) toner images are primarily transferred so as to be superimposed on the surface of the intermediate transfer belt 21 of the intermediate transfer mechanism 20, and then the intermediate transfer belt 21 is used as a recording medium. By performing secondary transfer to the recording paper P side, a so-called full-color image can be formed.
[0021]
Each of the image forming units 10 forms the above-described four color toner images by an electrophotographic process, and is arranged in a horizontal state at a substantially central portion of the image forming apparatus main body 1. Has been. Each image forming unit 10 basically has a photosensitive drum 11 as an image carrier that is rotationally driven at a predetermined speed in the direction of arrow A, and a roll that uniformly charges the surface of the photosensitive drum 11. Type charging device 12, ROS 13 as a latent image forming device that forms an electrostatic latent image by exposing a light image corresponding to image information to the surface of photosensitive drum 11 after charging, and two electrostatic latent images. The developing device 14 for developing with toner of a predetermined color in the component developer G, the roll type transfer device 15 for transferring the toner image formed by the development to the intermediate transfer belt 21, and the surface of the photosensitive drum 11 are cleaned. A drum cleaner 16 is similarly provided.
[0022]
Among them, the charging device 12 applies a predetermined charging potential: V on the surface of the photosensitive layer of the photosensitive drum 11 from a power supply device (not shown) to the charging roll. _H A charging voltage for charging is applied. The ROS 13 emits laser beams LB-Y, LB-M, LB-C, and LB-K emitted from four semiconductor lasers (not shown) according to image signals separated for each color through a predetermined optical system. After the rotary polygon mirror 17 is irradiated and deflected and scanned, scanning exposure is performed obliquely from below on each of the opposing photosensitive drums 11 via a plurality of reflection mirrors (not shown). Reference numeral 18 in the drawing is a transparent window for transmitting and emitting each laser beam LB from the housing sealed box 13a. Each developing device 14 is a two-component developing type developing device that performs development using a two-component developer G composed of a non-magnetic toner of each color component and a magnetic carrier, and has a configuration as described later. is there. In addition, each of the developing devices 14 is provided by a toner replenishing device (70) described later from a detachable / replaceable toner cartridge 19Y, 19M, 19C, or 19K as a toner container in which replenishing toner and a carrier are accommodated. An appropriate amount of toner and carrier are supplied. Further, a primary transfer bias having a polarity opposite to the charging polarity of the toner image on the photosensitive drum 11 is applied to the transfer device 15 (transfer bias roll) from a bias power source (not shown).
[0023]
In each of these image forming units 10, the surface of the rotating photosensitive drum 11 is charged with a predetermined charging potential: V by the charging device 12. _H Then, the charged surface is scanned and exposed with a laser beam LB corresponding to the image signal color-separated from the ROS 13 to thereby obtain a predetermined latent image potential: V _L After that, the latent image is developed with toner of each color in the two-component developer G supplied from the developing device 14 under the application of a developing bias. Finally, the toner image is electrostatically and sequentially primary transferred onto the surface of the intermediate transfer belt 21 that passes between the photosensitive drum 11 and the transfer device 15. Further, the surface of the photosensitive drum 11 after the transfer is cleaned by a blade of a drum cleaner 16 or the like.
[0024]
Further, as shown in FIG. 1, the intermediate transfer mechanism 20 stretches an endless intermediate transfer belt 21 on a plurality of rolls including a secondary transfer backup roll 22 and a drive roll 23, and drives the intermediate transfer belt 21. The roll 23 is rotated in the direction of arrow B by the rotational power of the roll 23. In addition, the transfer device 15 is disposed at a position on the inner peripheral surface of the intermediate transfer belt 21 opposite to the position where the photosensitive drum 11 comes into contact with the photosensitive drum 11 so that the belt 21 is pressed against the photosensitive drum 11. Each primary transfer portion is configured. Reference numeral 24 in FIG. 1 denotes a belt cleaner that cleans the surface of the intermediate transfer belt 21. In addition, around the intermediate transfer belt 21, a belt home position detection device for detecting a belt home mark formed at the belt side end, and a direction orthogonal to the belt rotation direction B at the belt one side end position. A belt walk detection device for detecting a deviation (a deviation or meandering) is provided.
[0025]
Further, a secondary transfer roll 30 that presses the intermediate transfer belt 21 against the roll 22 is disposed at a position facing the backup roll 22, and a belt from a bias power source (not shown) is provided on the peripheral surface of the backup roll 22. The power supply roll 31 to which a secondary transfer bias having the same polarity as the charged polarity of the toner image on the toner 21 is supplied is disposed so as to directly contact, thereby forming a secondary transfer portion. Reference numeral 32 in the drawing is a roll cleaner that cleans the surface of the secondary transfer roll 30.
[0026]
The toner image (multiple) transferred to the intermediate transfer belt 21 of the intermediate transfer mechanism 20 is transferred to the secondary transfer roll 30 that faces the backup roll 22 as the belt 21 rotates. It is conveyed to the next transfer section. Then, the toner image on the intermediate transfer belt 21 is sent out from the paper storage tray 40 in accordance with the image formation and secondary transfer timing of the toner image, and is fed through a paper feed path in which a roll 41, a resist roll 42, and the like are arranged. The recording sheet P having a predetermined size conveyed to the next transfer portion (between the intermediate transfer belt 21 and the secondary transfer roll 30) is electrostatically subjected to secondary transfer. The residual toner remaining without being transferred to the intermediate transfer belt 21 after the secondary transfer is cleaned and removed by the belt cleaner 24. 1 indicates the conveyance path of the recording paper P.
[0027]
Subsequently, the recording paper P onto which the toner image has been transferred from the intermediate transfer belt 21 is naturally peeled off from the intermediate transfer belt 21 portion in the secondary transfer portion, and then sent to the roll nip type fixing device 45, and the fixing device. The toner image is heat-fixed by passing through a fixing nip formed by a heating roll 46 and a pressure roll 47 at 45. Then, the recording paper P after the fixing process is completed is discharged out of the apparatus main body 1 (paper discharge portion) through a paper discharge path in which a discharge roll 48 and the like are provided.
[0028]
Through this process, a color image is formed on the recording paper P by this color printer. Incidentally, in this printer, for example, it is possible to form a black and white image on the recording paper P by operating only the black image forming unit 10K among the four image forming units.
[0029]
Further, the developing device 14 and the toner replenishing device 70 used in each image forming unit 10 in this color printer are configured as follows.
[0030]
First, as shown in FIGS. 3 to 5, the developing device 14 includes a developing device housing 50, a developing roll 51 disposed on the photosensitive drum 11 side of the housing 50, and a rear lower side of the developing roll 51. Augers 52 and 53 as developer agitating and conveying means, a paddle 54 as a developer supplying means for supplying the two-component developer G agitated and conveyed by the augers 52 and 53 to the developing roll 51 side, and The main part is composed of a trimmer 55 that regulates the layer thickness of the two-component developer G that is supplied and conveyed in a state where a magnetic brush is formed from the paddle 54 to the developing roll 51. The paddle 54 is not particularly required when the developer G can be supplied from the auger 52 to the developing roll 51.
[0031]
Among these, the developing roll 51 includes a cylindrical sleep made of a nonmagnetic conductive material and a magnet roll disposed in the hollow of the sleeve. A predetermined developing bias (for example, a voltage in which alternating current is superimposed on direct current) is applied to the sleeve from a developing bias power source (not shown). Further, a partition plate 56 is provided at a portion between the augers 52 and 53 of the housing 50 in a state where passages 57a and 57b are formed at both ends thereof. 4 and 5, reference numeral 50 a denotes a developer receiving portion that receives a developer replenished from the toner replenishing device, and 50 b denotes a so-called trickle developing system that discharges and collects the deteriorated developer so as to overflow little by little. The developer discharge part is shown.
[0032]
In such a developing device 14, the two-component developer G accommodated in the housing 50 is circulated and conveyed while passing through the passages 72 a and 72 b while being agitated by the rotational drive of the augers 52 and 53. At this time, the toner of the developer G is frictionally charged to a predetermined polarity by being mixed and stirred with the carrier. Subsequently, in the developing device 14, the developer G is supplied to the side of the developing roll 51 via the paddle 54 and is carried in a state where a magnetic brush is formed, and the layer thickness passes through a position immediately below the trimmer 55 to be predetermined. The thickness is regulated. Then, when the developer G after the regulation of the layer thickness is conveyed to the developing area facing the photosensitive drum 11 by the rotation of the developing roll 51, the developing electric field formed by the developing bias applied to the developing roll 14 is applied. Only the toner adheres electrostatically to the latent image portion of the photosensitive drum 11 so that development is performed.
[0033]
The developing device 14 is provided with a magnetic sensor 60 as a toner concentration sensor for detecting the toner concentration: TC of the two-component developer G accommodated in the housing 50.
[0034]
The magnetic sensor 60 is of a type that detects a toner concentration by detecting a change in magnetic permeability due to the developer G in the housing 50, and has a main body 61 and a sensor 62 that protrudes from the main body 61. The developing device housing 50 is attached to the outer wall portion on the side where the auger 53 is located. Specifically, the sensor unit 62 (detection surface 62a) is attached so as to be exposed on the same surface as the inner surface 50c of the housing. According to the magnetic sensor 60, an analog output voltage corresponding to a change in magnetic permeability due to the two-component developer and a change in toner density can be obtained as a sensor output value. That is, as illustrated in FIG. 7, when the toner is sufficient and the toner concentration: TC is high, a small output voltage is obtained, and conversely, when the toner is low and the toner concentration: TC is low, a large output is obtained. A voltage is obtained. The sensor output value of the magnetic sensor 60 is input to a control device (80) to be described later and used for required control processing.
[0035]
On the other hand, the toner replenishing device 70 is of a type that replenishes the developing device 14 with toner and carrier (hereinafter referred to as “toner etc.”) because the trickle developing method is employed. The toner replenishing device 70 includes a holder 71 that detachably holds the toner cartridge 19 and a developer transport pipe 72 that transports toner discharged from the toner cartridge 19 to the developer receiving portion 50a of the developing device 14. And an auger or agitator as a developer agitating and conveying member (not shown) that rotates in the toner cartridge 19 and an agitator as a developer conveying member (not shown) that rotates in the developer conveying pipe 72. The main part is composed of a drive device 73 provided with an electric motor, a drive transmission gear mechanism and the like.
[0036]
Among these, for the developer transport pipe 72, the first transport pipe 72 a disposed on the end side where the toner discharge port of the toner cartridge 19 is located, the one end of the first transport pipe 72 a, and the developer of the developing device 14. The second transport pipe 72b disposed between the receiving portion 50a (receiving port) and the receiving portion 50a is combined. Reference numeral 75 in the figure denotes a drive transmission shaft that transmits the rotational power of the driving device 73 to the auger of the first transport pipe 72a, and 76 denotes a drive transmission that transmits the rotational power between the drive transmission shaft 75 and the auger of the first transport pipe 72a. A gear mechanism 77 is a drive transmission gear mechanism that transmits the rotational power of the auger of the first transport pipe 72a to the agitator of the second transport pipe 72b.
[0037]
In the toner replenishing device 70, when the toner replenishment timing based on the detection information of the magnetic sensor 60 comes as will be described later, the driving device 73 is started and the agitator in the toner cartridge 19 and the developer conveying pipes 72a and 72b are in operation. The auger or agitator is driven to rotate, whereby the toner or the like in the toner cartridge 19 is sent to the developer receiving portion 50a of the developing device 14 through the developer transport pipes 72a and 72b.
[0038]
In this color printer, required control based on detection information from the magnetic sensor 60 and the like is performed.
[0039]
FIG. 6 is a block diagram showing the main configuration of the control system. Reference numeral 80 in FIG. 6 denotes a central control unit including an arithmetic processing unit, a memory storing a control program and detection data, and the like. The central controller 80 includes a magnetic sensor 60 attached to each developing device 14, a pixel counter 65 that counts pixels of a print image, a power switch or an interlock of the printer main body (a front door of the printer main body 1). The switch 66 and the like which are operated by the opening / closing operation are connected, and necessary detection information and the like are inputted from these connected products. The central controller 80 also controls a controller 81 for controlling the operation of the drive device 73 in the toner replenishing device 70 and a latent image potential V _L Controller 82 for controlling the variable maximum value (maximum output value or maximum exposure amount), and charging potential in charging device 12: V _H Controller 83 for controlling the size of the developing device, and developing bias in developing device 14: V _D Is connected to a controller 84 for controlling the size of the display, and a display device 85 including a liquid crystal panel and a display lamp for performing a required display, and a required control signal from the control device 80 is connected to each of these connection destinations. It is output.
[0040]
In particular, as shown in FIGS. 1 and 8 to 9, the central control device 80 performs control (toner density sensor) related to the replenishment operation of the toner replenishing device 70 based on the detection information of the magnetic sensor 60, and the detection thereof. Based on the information, it is determined that the toner cartridge 19 is empty (empty detection), and when it is determined that the remaining amount of toner in the developing device 14 has decreased, the image forming operation is forcibly terminated (shutdown). ) Is controlled.
[0041]
In the central controller 80, as shown in FIG. 1 and FIGS. 8 to 10, when the toner cartridge 19 is detected to be empty and the image forming operation is shut down, the latent image potential: V _L And development bias: V _D Potential difference (contrast potential): V _cont 2 is the contrast potential at normal time: V _cont 1 (> V _cont Control (final adjustment of latent image potential) is performed so that the value is smaller than 2). In this embodiment, the control is performed using a variable maximum value of the latent image potential: V _L 2 is the variable maximum value in normal time: V _L 1 (> V _L This is realized by changing to a value smaller than 2). For example, as illustrated in FIG. 10a, the charging polarity of the toner is negative, and the charging potential is V _H Is "-700V", development bias: V _D Is “−560V”, the variable maximum value V of the latent image potential in normal times _L If 1 is set to “−210 V”, the variable maximum value V of the latent image potential after the sky detection is detected. _L Change 2 to "-260V".
[0042]
Further, in this central control device 80, the variable maximum value V of the latent image potential in normal time from a predetermined time before the empty detection of the toner cartridge 19 is detected. _L 1 is a small variable maximum value V that should be changed after the sky is detected _L The control is performed so as to gradually approach 2 (latent image potential pre-adjustment).
[0043]
1 and 7 to 9, the symbol α is a toner concentration value that is a target value at the time of toner concentration control using the toner concentration sensor 60, and β is a toner concentration value that is a determination reference (threshold value) when performing empty detection. , Γ is a toner density value that serves as a judgment criterion when performing shutdown, and η is a toner density that serves as a judgment standard when performing pre-adjustment of the latent image potential. These toner density values α, β, γ, and η are in a magnitude relationship of “α>η>β> γ”. For example, α = 10%, η = 9%, β = 7%, γ = 5. % Can be set.
[0044]
Next, the operation of the color printer provided with the control device 80 will be described with reference to the flowchart shown in FIG.
[0045]
First, when the printing operation by the printer is started, detection of the toner density by the magnetic sensor 60 is executed at a predetermined sampling timing set in advance. _TC Is smaller than a voltage value corresponding to the target value α (10%) of the toner density sensor (step S101). At this time, sensor output value: V _TC Is determined to be a voltage value higher than the target toner density α, the toner density in the developing device 14 is considered to be sufficient, and the toner replenishment operation or the like is not executed. When it is determined that the voltage value is small, a control signal is sent from the control device 80 to the controller 81 of the toner replenishing device 70, and a toner replenishing operation is executed (S102). That is, as described above, the driving device 73 of the toner replenishing device 70 is driven for a predetermined time, so that toner or the like is supplied from the toner cartridge 19 to the developing device 14 by a predetermined amount (see FIG. 5).
[0046]
When the toner concentration is detected by the magnetic sensor 60, the sensor output value of the magnetic sensor 60: V _TC Is smaller than a voltage value corresponding to the toner density value η (= 9%) (S103), and its sensor output value: V _TC Is determined to be a voltage value larger than the toner density value η, the process returns to step S101, and the sensor output value: V _TC The toner replenishing operation is repeated until the voltage returns to a voltage value corresponding to the toner density value α (see FIG. 9). Thus, during normal times, the toner concentration TC of the two-component developer G in the developing device 14 is controlled so as to be substantially maintained at a predetermined value (α).
[0047]
Conversely, in step S103, the sensor output value: V _TC Is determined to be a voltage value smaller than the toner density value η, a control signal is sent from the controller 80 to the latent image potential controller 82 of the ROS 13 to perform pre-adjustment of the latent image potential (S104). . In this embodiment, the sensor output value: V, as indicated by the straight diagonal line consisting of the solid line in FIG. _TC The variable maximum value of the latent image potential is changed in direct proportion to the change in. That is, at this time, as shown in FIG. 9, the remaining amount of toner or the like in the toner cartridge 19 decreases, and the sensor output value: V _TC Therefore, the variable maximum value V of the latent image potential is also changed in the normal state. _L Variable maximum value V after 1 when empty is detected _L Change control is carried out so that it falls correspondingly to 2.
[0048]
During the pre-adjustment relating to such a latent image potential, the sensor output value: V _TC Is smaller than a voltage value corresponding to the toner density value β (= 7%) (S105), and its sensor output value: V _TC The pre-adjustment is continued while the voltage value exceeds the voltage value corresponding to the toner density β, but when it is determined that the voltage value is smaller than the voltage value corresponding to the toner density β, that is, the sky is detected. In this case, the pixel counter 65 starts counting the number of pixels in the printing operation after the sky detection (S106), and the variable maximum value of the latent image potential is a small variable maximum value V after the sky detection. _L Finally, it is changed to 2 (S107). Moreover, when this empty detection is made, a control signal is sent from the control device 80 to the display device 85, and a warning message such as “Please replace the toner cartridge” is displayed on the display device 85 (see FIG. S108).
[0049]
Thereafter, whether the power of the printer main body is turned on / off (OFF) or the front door is opened / closed for the replacement operation of the toner cartridge 19, and the interlock switch 66 is turned on / off. Is determined (S109), and when it is determined that there is an on / off operation, the above control ends. That is, when the on / off operation is confirmed, the supply of the developer from the toner cartridge 19 to the developing device 14 by the toner replenishing device 70 is executed until the sensor output value recovers to the target value α, and the latent image potential. The variable maximum value of V is the normal value V _L After returning to 1, it ends.
[0050]
However, if it is not confirmed in step S109 that the on / off operation is performed, the counter value (integrated value) of the pixel counter 65 is set in advance to a predetermined value N (the number of pixels to be shut down: this is the toner density γ It is determined whether or not (S110). At this time, while it is determined that the counter value is smaller than the specified value N, the process returns to step S109 to continue the determination as to whether or not the power source or the interlock switch 66 is on / off. When it is determined that the counter value has reached the specified value N or more, the image forming operation by the printer is shut down (S111). Thereafter, the image forming operation is not resumed unless the toner cartridge 19 is replaced. Note that the determination of the shutdown is performed in place of the method of determining based on the pixel count after the sky detection in step S110, and whether or not the toner density becomes “γ = 5%” which is the above-described determination criterion in the same step. You may comprise so that it may judge based on.
[0051]
As described above, in this printer, when the toner cartridge 19 is empty and before the image forming operation is shut down, as shown in FIG. Value: V _L 1 (-210V) is smaller than that variable maximum value: V _L 2 (−260V), the contrast potential (| V _H -V _L 1 |): V _cont 1 (350V) is lower than that for the contrast potential (| V _H -V _L 2 |): V _cont 2 (300V) is changed (see FIGS. 1 and 9). At this time, as shown in FIG. _H (-700V) and development bias: V _D Since (-560V) is not changed, the potential difference between the two (| V _H -V _D |): V _cln Is kept constant.
[0052]
As a result, image formation between the sky detection and the shutdown is performed under the conditions such as the contrast potential as described above, so that both the BCO in the image and the background fog do not occur, and the image quality is good. Image formation is possible. Moreover, in this printer, the variable maximum value of the latent image potential is gradually changed to a small variable maximum value from the time before the sky detection (when the toner density is “η” or less) to the sky detection. For this reason, the potential difference between the latent image potential and the developing bias at that time gradually becomes a small value, so that a rapid change in image density does not occur, and this makes it possible to form an image with good image quality. Incidentally, as indicated by a two-dot chain line in FIG. 1, when the toner density TC becomes 7% (β) and the sky is detected, the variable maximum value of the latent image potential is changed to a small variable maximum value. The potential difference between the latent image potential and the developing bias may be changed from 350 V to 300 V at a time.
[0053]
Tables 1 and 2 below show the results of tests performed using this printer. Table 1 shows the test results conducted in a high humidity environment (85% relative humidity), and Table 2 shows the test results conducted in a low humidity environment (10% relative humidity). In this test, the charging potential and the developing bias potential are fixed in any environment, the variable maximum value of the latent image potential is changed to change the contrast potential, and the toner density TC as shown in the table is set. Test printing was performed under certain conditions, and the occurrence of BCO in the image and background fogging in the printed matter at that time was examined. Note that the contrast potential during normal operation was set to “350 V”. Considering that the detection accuracy of the magnetic sensor 60 has an error of ± 1%, when the toner density is “7.0%”, “near empty detection time” and the toner density is “5.0%”. And “4.0%” was set as the vicinity at the time of shutdown. “◯” in the table indicates that the BCO and fog are not generated at all, “×” indicates that the BCO and fog are generated, and “−” indicates that the test is not performed.
[0054]
[Table 1]

[0055]
[Table 2]

[0056]
As is apparent from the results of Tables 1 and 2, when the toner density value (5%, 4%) corresponding to the period from the empty detection to the shutdown, the contrast potential (350 V) is normal. In particular, BCO is generated in the image, but when the contrast potential is reduced (300 V, 250 V), it can be seen that BCO is not generated in the image. It can also be seen that the occurrence of BCO in the image between this sky detection and shutdown is more likely to occur in the high humidity environment of Table 1 than in the low humidity environment of Table 2. Incidentally, it can be seen that in a low-humidity environment, when the contrast potential is set to “400 V” as shown in Table 2, BCO in the image tends to occur.
[0057]
[Other embodiments]
In the first embodiment, regarding the pre-adjustment of the latent image potential, the variable maximum value of the latent image potential: V _L By changing 1 to a value that is gradually proportional to the decrease in toner density (TC) and gradually decreasing, the contrast potential: V _cont In the present invention, as shown in FIG. 11, the variable maximum value of the latent image potential is made to correspond to the decrease in the toner density. The contrast potential at that time is V _cont Alternatively, control may be performed so as to decrease stepwise. In this case, the ratio at which the contrast potential is decreased stepwise may be set as appropriate. For example, as illustrated in FIG. 11, the contrast potential: V every time the toner density TC decreases “0.5%”. _cont Can be set to be smaller by “10V”.
[0058]
Even in this configuration, as in the case of the first embodiment, the contrast potential at that time gradually becomes a small value step by step, so that the image density in the image formation from the sky detection to the shutdown is reduced. Rapid fluctuation occurs But Therefore, it is possible to form an image with good image quality.
[0059]
In the first embodiment, the contrast potential between the sky detection and the shutdown is V _cont As a technique for reducing the latent image potential, the variable maximum value of the latent image potential: _L However, in the present invention, as illustrated in FIG. 12, the charging potential: V is exemplified. _H And development bias: V _D It is also possible to perform control for appropriately changing the potential. In this case, charging potential: V _H And development bias: V _D Is the potential difference between the charging potential and the developing bias: V _cln1 Are preferably changed by the same amount so that the background voltage is kept at a voltage value that hardly causes background fogging. For example, as illustrated in FIG. 12, the charging potential is changed from −700 V in normal times to −650, and the developing bias is set to −5 in normal times. 6 It can be changed from 0V to -500V.
[0060]
Even in this configuration, the contrast potential in the normal state: V from the detection of the sky to the shutdown. _cont1 (3 1 0V) is changed to 250V and becomes smaller. Accordingly, in the meantime, as in the case of the first embodiment, it is possible to form an image with good image quality in which neither the BCO in the image nor the background fog is generated. In this case, the variable maximum value of the latent image potential: V _L As for, as long as the contrast potential does not hinder the decrease, the necessary amount may be changed.
[0061]
Further, in this configuration, when the development potential alone is changed under the above conditions without changing the charging potential, background fog is less likely to occur, but the reverse polarity is caused by the injection of charges. This is not suitable because a problem arises in that a carrier charged on the photosensitive drum adheres to a portion (background portion) other than the electrostatic latent image on the photosensitive drum.
[0062]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, even in the image forming apparatus of the type that uses the toner density sensor to detect emptyness of the toner container, the image forming operation is performed after particularly detecting emptyness. It is possible to easily and reliably prevent the background fogging and the BCO in the image from occurring until the image is forcibly terminated. In particular, since the BCO in the image can be reliably prevented, it is possible to avoid the occurrence of white spots or streaks in the image due to the BCO in the image.
[Brief description of the drawings]
FIG. 1 is a correlation diagram showing a relationship between toner density and contrast potential according to control details in Embodiment 1. FIG.
FIG. 2 is a schematic diagram illustrating a color printer according to the first embodiment.
FIG. 3 is a schematic longitudinal sectional view of the developing device.
FIG. 4 is a schematic cross-sectional view of the developing device.
FIG. 5 is a perspective view illustrating a developing device and a toner supply device.
FIG. 6 is a block diagram showing the configuration of a control system that uses detection information such as a toner density sensor.
FIG. 7 is an output characteristic diagram of a toner density (magnetic) sensor.
FIG. 8 is a flowchart showing main control contents by the control system of FIG. 6;
FIG. 9 is an explanatory diagram illustrating a relationship between a change in toner density with respect to a print amount and control items.
FIGS. 10A and 10B show the contents of control in the first embodiment, where FIG. 10A is an explanatory diagram showing each potential state in a normal state, and FIG. Illustration.
FIG. 11 is a correlation diagram showing a relationship between toner density and contrast potential according to control content in another embodiment.
FIGS. 12A and 12B show control contents in another embodiment, in which FIG. 12A is an explanatory diagram showing each potential state in a normal state, and FIG. 12B shows each potential state during the period from empty detection to shutdown. Illustration.
FIGS. 13A and 13B show the control contents of the prior art, in which FIG. 13A is an explanatory diagram showing each potential state in a normal state, and FIG. 13B is a diagram showing each potential before it is determined that the remaining amount of toner is low and the printing operation is stopped. Explanatory drawing which shows an electrical potential state.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Photosensitive drum (image carrier), 13 ... ROS (latent image forming device), 14 ... Developing device, 19 ... Toner cartridge (toner container), 60 ... Magnetic sensor (toner density sensor), 70 ... Toner replenishing device , 80... Control device (control means), V _H ... Charging potential, V _D ... Development bias, V _L ... Latent image potential, V _cont 1 ... Contrast potential in normal times (potential difference between latent image potential and developing bias), V _cont 2: Contrast potential after change, G: Two-component developer.

Claims (2)

An image carrier charged to a predetermined charging potential, a latent image forming device for forming an electrostatic latent image having a predetermined latent image potential corresponding to image information on the image carrier, and the latent image forming device A developing device that develops the formed electrostatic latent image in a state where a two-component developer composed of toner and a carrier is supplied and a developing bias is applied, and toner replenishment that replenishes the toner from the toner container And a toner concentration sensor for detecting the toner concentration in the two-component developer contained in the developing device, and at least controlling the toner replenishing device based on detection information from the toner concentration sensor, Based on the detection information, it is determined that the toner container is empty, and after that determination, the image forming operation is forcibly terminated when it is determined that the remaining amount of toner in the developing device has decreased. In the image forming apparatus and a control means for controlling that,
The control means determines that the potential difference between the latent image potential and the developing bias is normal when the toner container is empty and after the image forming operation is forcibly terminated. An image forming apparatus that performs control to change a variable maximum value determined by the latent image forming apparatus of the latent image potential to a value smaller than the variable maximum value in normal time so that the latent image potential becomes a smaller value. . The image forming apparatus according to claim 1.
The control means gradually or steps the variable maximum value of the latent image potential from the predetermined time before determining that the toner container is empty to the small variable maximum value to be changed after the determination. An image forming apparatus that performs control to change so as to be closer together.

Images