JP2004268436A - Image formation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure a stable gradational characteristic by impressing an optimum bias current to a laser element even when a quantity of laser light is changed by a variation of the photoreceptor sensitivity or the like. <P>SOLUTION: An image formation device has the laser element 31 as a light source, and forms an image by supplying a bias current and a laser driving current corresponding to image data to the laser element 31, guiding a modulated laser light onto a photoreceptor, and carrying out scanning exposure. The bias current to be impressed to the laser element 31 is controlled according to an emission quantity of the laser element 31. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２９】
本発明の他の実施の形態においては、例えば、ある発光量において１画素毎にオン／オフを繰り返すパターンで露光し、その結果低下した感光体１の帯電電位の検出が電位検出器９より行われる（図２参照）。
【００３０】
又は、現像手段４の現像により形成されたトナー像の濃度の検出がトナー検出器１０により行われる（図２参照）。
【００３１】
帯電電位またはトナー像濃度の検出結果が所定の値と一致するようにバイアス電流を設定する。この後、順次、発光量を変えて上記動作を行い、発光量とバイアス電流設定電圧との対応テーブルを作成し、記憶手段へ記憶させる。なお、露光パターンは例えばパルスデューティ５０％のパルス幅変調でも良い。
【００３２】
以上に説明した画像形成装置のレーザ光の制御は、半導体レーザの発光量に応じて半導体レーザに印加するバイアス電流を制御するものであるから、従来、問題であった中間調画像を鮮明に形成でき、安定した画質の画像形成装置が提供される。
【００３３】
なお、本発明は、実施の形態に限定されるものではなく、請求項に記載した範囲内で変更、変形が可能である。
【００３４】
【発明の効果】
本発明により、感光体感度等の変動によりレーザ光量が変化しても、半導体レーザに最適なバイアス電流を印加する事によって、安定した階調性を確保できる。
【図面の簡単な説明】
【図１】画像形成装置の概略構成図。
【図２】画像形成手段の構成図。
【図３】レーザ走査露光の光学系の一例を示す斜視図。
【図４】レーザ素子の発光特性図。
【図５】半導体レーザの発光量が変化した場合の画像濃度を示す特性図。
【図６】駆動ＩＣを用いた制御回路のブロック図。
【符号の説明】
１ 感光体
３ 像露光手段（書き込み手段）
４ 現像手段
７ 除電器
８ 温度検出器
９ 電位検出器
１０ トナー検出器
３１ レーザ素子
３２ コリメートレンズ
３３ スリット
３４ シリンドリカルレンズ
３５ 回転多面鏡
３６ ｆθレンズ
３７ 補正用シリンドリカルレンズ
３８ カバーガラス
４０ レーザ光源ユニット
４１ 駆動ＩＣ
４２ Ｄ／Ａコンバータ
４３ ＣＰＵ
Ａ 画像形成装置
Ｉｔｈ 閾値電流
Ｌ レーザビーム
ＬＤ レーザ素子
ＰＤ フォトダイオード[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus that modulates a laser beam and scans and exposes a photoreceptor to form an image in an image forming apparatus such as a digital copying machine or a printer. The present invention relates to an image forming apparatus that supplies a modulated laser beam to a charged photoconductor, scans and exposes the laser beam, forms a latent image, and reversely develops the latent image to form an image.
[0002]
[Prior art]
Several methods have been conventionally proposed to improve the response characteristics of a semiconductor laser.
[0003]
Patent Literature 1 proposes a method of controlling an optimum bias current by switching a resistance value of a bias current setting circuit so that a minimum density image can be formed in a state where a semiconductor laser is subjected to pulse width modulation with a pulse duty of 30% or less. ing.
[0004]
Patent Document 2 proposes a method of switching a bias current target value for a plurality of image forming modes to control a bias current without changing a laser light amount.
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-187374
[Patent Document 2]
JP 2000-355117 A
[Problems to be solved by the invention]
However, in the method of setting the bias current based on the minimum density image at the time of pulse width modulation, attention is paid only to the correction of the minimum density, so that the halftone gradation is insufficient. Further, in the method of controlling the bias current in the image forming mode, even when the laser light amount changes, the bias current is fixed for each mode, so that the response characteristic of the semiconductor laser changes and the image quality may be significantly deteriorated. There is.
[0008]
SUMMARY OF THE INVENTION It is an object of the present invention to realize stable gradation even when the amount of laser light changes following the deterioration of the photoreceptor sensitivity.
[0009]
[Means for Solving the Problems]
The above object is achieved by the following image forming apparatus according to the present invention.
[0010]
(1) An image for forming an image by supplying a bias current and a laser drive current according to image data to the semiconductor laser using a semiconductor laser as a light source, guiding the modulated laser light onto a photoconductor, and performing scanning exposure to form an image. The image forming apparatus according to claim 1, further comprising a control unit configured to control the bias current applied to the semiconductor laser according to a light emission amount of the semiconductor laser.
[0011]
(2) Using a semiconductor laser as a light source, supplying a bias current and a laser driving current according to image data to the semiconductor laser, guiding the modulated laser light onto the photoconductor charged by the charging means, and performing scanning exposure. An image forming apparatus for forming an image by means of a potential detecting means for detecting a potential on the charged photoconductor, and a correction coefficient for a bias current applied to the semiconductor laser in accordance with a light emission amount of the semiconductor laser. A correction coefficient generation unit that guides the laser beam modulated by predetermined modulation data during the non-image forming period onto the photoconductor, performs scanning exposure, and performs the correction coefficient based on a detection result of the potential detection unit. An image forming apparatus, comprising: a control unit for generating a bias current and controlling a bias current applied to the semiconductor laser according to an amount of light emitted from the semiconductor laser.
[0012]
(3) An image for forming an image by supplying a bias current and a laser driving current according to image data to the semiconductor laser using a semiconductor laser as a light source, guiding the modulated laser light onto a photoconductor, and performing scanning exposure to form an image. In the forming apparatus, a toner detecting unit for detecting an amount of toner adhered on the photoconductor that has been developed, and a correction coefficient generating unit for generating a correction coefficient for a bias current applied to the semiconductor laser in accordance with an emission amount of the semiconductor laser Having a laser light modulated by predetermined modulation data during a non-image forming period, is guided on the photosensitive member for scanning exposure, and generates the correction coefficient based on a detection result of the toner detection unit, An image forming apparatus comprising: a control unit configured to control a bias current applied to the semiconductor laser according to a light emission amount of the semiconductor laser.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the image forming apparatus of the present invention will be described with reference to the drawings.
[0014]
FIG. 1 is a schematic configuration diagram of an image forming apparatus, and FIG. 2 is a configuration diagram of an image forming unit.
[Image forming apparatus]
The image forming apparatus A includes an image forming unit in which a charging unit 2, an image exposing unit (writing unit) 3, a developing unit 4, a transfer unit 5A, a charge removing unit 5B, and a cleaning unit 6 are arranged around a rotating photoreceptor 1. Having. The image forming unit forms a latent image by performing an exposure scan based on image data read from a document by the laser beam L of the image exposure unit 3 after uniformly charging the surface of the photoconductor 1 by the charging unit 2. Then, the latent image is reversely developed by the developing means 4 to form a toner image on the surface of the photoconductor 1.
[0015]
The sheet S fed from the sheet storage unit 11 is sent to a transfer position. At the transfer position, the toner image is transferred onto the sheet S by the transfer unit 5A. Thereafter, the paper S is erased from the photoreceptor 1 by removing the electric charge on the back surface by the charge removing means 5B, transported by the transport unit 12, subsequently heated and fixed by the fixing means 13, and discharged from the paper discharge roller 14.
[0016]
When performing image formation on both sides of the sheet S, the sheet S heated and fixed by the fixing unit 13 is branched from the normal sheet discharge path by the transfer path switching plate 15, and is switched back in the reverse transfer unit 16 to be turned on the front and back. After reversing, the sheet S passes through the image forming section again, forms an image on the back surface of the sheet S, and is discharged from the sheet discharging roller 14 through the fixing unit 13 to the outside of the apparatus.
[0017]
The developer remaining on the surface of the photoreceptor 1 after the image processing is removed by the cleaning unit 6, and the surface of the photoreceptor 1 is made uniform by static elimination by the static eliminator 7. To end.
[0018]
A temperature detector 8 and a potential detector 9 are disposed between the laser beam L and the developing device 4, and a toner detector 10 is disposed between the developing device 4 and the paper feeding unit. A later-described potential and a toner adhesion amount are detected to control a bias current described later.
[0019]
[Optical system for laser scanning exposure]
In a digital image forming apparatus such as a digital copying machine or a printer, the photosensitive member 1 is usually scanned and exposed with a laser beam L to form an image. FIG. 3 is a perspective view showing an example of an optical system for this laser scanning exposure.
[0020]
A laser beam L emitted from a laser element 31 composed of a semiconductor laser is collimated by a collimating lens 32, then is deflected by a rotating polygon mirror 35 through a slit 33 and a cylindrical lens 34, and is deflected by an fθ lens 36 and a correcting cylindrical lens 37. The laser beam L is imaged on the photoreceptor 1 (shown in FIG. 1), is exposed in the main scanning direction by the rotating polygon mirror 35, and performs sub-scanning by rotating the photoreceptor 1 to form an image. 38 is a cover glass.
[0021]
The light output of the laser element 31 in the image forming apparatus A using the laser light as described above is affected by fluctuations in the current flowing in the laser element 31, the ambient temperature, and the like. Therefore, the voltage obtained by detecting the light output of the laser element 31 is compared with a reference voltage, and automatic light output control for keeping the light output constant, that is, APC (Auto Power Control) is performed. At the same time, it becomes necessary to increase the response speed of the laser emission control system, and there is a method of supplying a bias current to the laser element 31 in advance.
[0022]
FIG. 4 is an emission characteristic diagram of the semiconductor laser. When the optical output P of the semiconductor laser is plotted on the ordinate and the driving current I is plotted on the abscissa, the laser emits sharply when the current flowing through the semiconductor laser exceeds the threshold current Ith. Then, the LED emits light.
[0023]
Therefore, if a bias current that is equal to or less than the threshold current Ith and is as close as possible to the threshold current Ith is supplied in advance, the response characteristics of light emission of the semiconductor laser are improved. The bias current value makes it possible to appropriately control particularly the halftone gradation.
[0024]
FIG. 5 is a characteristic diagram showing the image density when the light emission amount of the semiconductor laser changes. When the density data X is plotted on the horizontal axis and the image density D is plotted on the vertical axis, the image density changes when the light emission amount of the semiconductor laser changes when the bias current is constant.
[0025]
In recent years, a semiconductor laser light output control drive having excellent response characteristics has been marketed. For example, there is SN65ALS544 (registered trademark) manufactured by Texas Instruments.
[0026]
FIG. 6 is a block diagram of a control circuit using a driving IC. The control is basically performed by the CPU 43 which is a control means. The laser element LD as the light emitting light source and the photodiode PD for detecting the light output are the laser light source unit 40 of the same package, and the light detected by the photodiode PD The output signal is compared with the light amount setting reference voltage Vref by the drive IC 41, and automatic light output control (APC) for controlling the drive current of the semiconductor laser is performed. Note that the light amount setting reference voltage Vref changes according to the fluctuation of the photoconductor sensitivity and the like, and the APC is performed by changing the light emission amount of the semiconductor laser so as to have an appropriate maximum density. The bias current can be set by inputting the bias current setting voltage Vb to the bias terminal B of the driving IC 41. In the present invention, the D / A converter 42 is controlled by the CPU 43, and the output voltage of the D / A converter 42 is controlled. It is input to the drive IC 41.
[0027]
In the present embodiment, the bias current setting voltage Vb is input to the drive IC according to the light emission amount of the semiconductor laser according to the correction coefficient stored in advance, and the bias current is controlled. Table 1 shows an example of the correction coefficient.
[0028]
[Table 1]

[0029]
In another embodiment of the present invention, for example, exposure is performed in a pattern in which ON / OFF is repeated for each pixel at a certain light emission amount. (See FIG. 2).
[0030]
Alternatively, the density of the toner image formed by the development of the developing unit 4 is detected by the toner detector 10 (see FIG. 2).
[0031]
The bias current is set so that the detection result of the charging potential or the toner image density matches a predetermined value. Thereafter, the above operation is performed by sequentially changing the light emission amount, and a correspondence table between the light emission amount and the bias current setting voltage is created and stored in the storage means. The exposure pattern may be, for example, pulse width modulation with a pulse duty of 50%.
[0032]
Since the control of the laser beam of the image forming apparatus described above controls the bias current applied to the semiconductor laser according to the light emission amount of the semiconductor laser, a halftone image which has conventionally been a problem is clearly formed. Thus, an image forming apparatus with stable image quality is provided.
[0033]
The present invention is not limited to the embodiments, but can be modified and modified within the scope described in the claims.
[0034]
【The invention's effect】
According to the present invention, even when the amount of laser light changes due to a change in the sensitivity of the photoconductor, stable gradation can be secured by applying an optimum bias current to the semiconductor laser.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus.
FIG. 2 is a configuration diagram of an image forming unit.
FIG. 3 is a perspective view showing an example of an optical system for laser scanning exposure.
FIG. 4 is a light emission characteristic diagram of a laser element.
FIG. 5 is a characteristic diagram showing an image density when a light emission amount of a semiconductor laser changes.
FIG. 6 is a block diagram of a control circuit using a driving IC.
[Explanation of symbols]
1 Photoconductor 3 Image exposure means (writing means)
4 Developing means 7 Static eliminator 8 Temperature detector 9 Potential detector 10 Toner detector 31 Laser element 32 Collimating lens 33 Slit 34 Cylindrical lens 35 Rotating polygon mirror 36 fθ lens 37 Correcting cylindrical lens 38 Cover glass 40 Laser light source unit 41 Drive IC
42 D / A converter 43 CPU
A image forming apparatus Ith threshold current L laser beam LD laser element PD photodiode

Claims (4)

In an image forming apparatus, a semiconductor laser is used as a light source, a bias current and a laser driving current corresponding to image data are supplied to the semiconductor laser, and the modulated laser light is guided onto a photosensitive member to perform scanning exposure to form an image. ,
An image forming apparatus, comprising: control means for controlling the bias current applied to the semiconductor laser according to an amount of light emitted by the semiconductor laser. 2. The image according to claim 1, wherein the control unit controls the bias current applied to the semiconductor laser according to a light emission amount of the semiconductor laser according to a correction coefficient of the bias current stored in advance. 3. Forming equipment. A semiconductor laser is used as a light source, a bias current and a laser driving current corresponding to image data are supplied to the semiconductor laser, and a laser beam modulated on a photoconductor charged by a charging unit is guided and exposed by scanning to form an image. In the image forming apparatus to be formed,
A potential detecting means for detecting a potential on the charged photoconductor, and a correction coefficient generating means for generating a correction coefficient for a bias current applied to the semiconductor laser according to a light emission amount of the semiconductor laser; The laser beam modulated by predetermined modulation data during the formation period is guided on the photosensitive member for scanning exposure, and the correction coefficient is generated based on the detection result of the potential detecting means, and the light emission amount of the semiconductor laser is generated. An image forming apparatus, comprising: a control unit that controls a bias current applied to the semiconductor laser according to the above. In an image forming apparatus, a semiconductor laser is used as a light source, a bias current and a laser driving current corresponding to image data are supplied to the semiconductor laser, and the modulated laser light is guided onto a photosensitive member to perform scanning exposure to form an image. ,
A toner detection unit that detects an amount of toner adhered to the developed photoconductor, and a correction coefficient generation unit that generates a correction coefficient of a bias current applied to the semiconductor laser according to a light emission amount of the semiconductor laser; The laser light modulated by the predetermined modulation data during the non-image forming period is guided on the photosensitive member for scanning and exposure, and the correction coefficient is generated based on the detection result of the toner detection unit, and the correction coefficient of the semiconductor laser is adjusted. An image forming apparatus comprising: a control unit configured to control a bias current applied to the semiconductor laser according to a light emission amount.

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