JP3591144B2 - Image density detection method and apparatus, image density control method and apparatus, and image forming apparatus - Google Patents

Description

【００３４】
現像器制御部３２は、トナー像２５がイエロートナーで形成されている場合、濃度信号ａと目標値の３３％を比較し、かつ、補正濃度信号ｃを考慮した制御信号を発生して現像ロール駆動モータ３３とトナー供給用ディスペンサ用モータ３４の回転数を制御する。これによってトナー付着量が所定の値に制御される。
【００３５】
画像濃度制御部３５は、補正濃度信号ｃを入力すると、スコロトロン帯電器３のグリット電源３７およびレーザ出力部１の光量コントローラ３６を制御してスコロトロン帯電器３のグリット電圧およびレーザ出力部１より出射されるレーザー光の光量を所定の値にする。これによって静電潜像のコントラスト比が所定の値に制御される。
【００３６】
このようにして所定の画像濃度を有した品質の高い記録画像を得ることができる。
【００３７】
ここで、第１および第２の赤外ＬＥＤ２１、２４の点灯と第１および第２のホトダイオード２２、２３の出力の関係を整理すると、以下の通りである。
【表２】

【００３８】
以上、本発明の画像形成装置を実施の形態に基づいて説明したが、本発明はこの実施の形態に限定されるものではなく、例えば、以下の変形等が可能である。
（１） 読み取り用のカラーパッチを作らないで、通常の出力画像を用いてトナー像濃度検知を行ってもよい。
（２） 帯電量、露光量、現像バイアス、現像ロール回転数、トナー供給係数のうち少なくともいずれかの操作量を制御すれば良いが、これ以外の操作量を用いて もよい。また、画像濃度制御あるいはトナー補給制御以外の制御にも適用することができる。
（３） トナー濃度信号を、例えば、判断、警告表示、等に使用してもよい。
（４） 用紙上の転写像、中間転写体上のトナー像、あるいは定着後の画像の濃度を検出するようにしてもよい。
（５） 発光手段および受光手段の配置角度は、θ_１ ＞θ_２ でもよい。また、第２のホトダイオード２３を、感光体面の法線に対して、第１の赤外ＬＥＤ２１と同じ側に配置しているが、感光体面の法線に対して第１の赤外ＬＥＤ２１の反対側であってもよい。
（６） 発光手段として、例えば、ハロゲンランプ、レーザーダイオード、等を使用することができ、受光手段として、例えば、光電管、光電子増倍管、ホトコンダクター、等を使用することができる。
（７） 受発光手段に集光光学系を備えてもよい。
（８） 濃度演算は前述した減算に限定することなく、以下の除算や他の演算を用いてもよい。
【数１】

（９） 演算式｛（ａ−ｂ’）＋（ａ’−ｂ）｝／２の代わりに以下の演算式を用いても良い。
【表３】

（１０）受発光素子をそれぞれ、あるいは何れかを１つにし、正反射成分と拡散反射成分を受光できるように２つの位置間で移動できるようにしてもよい。
（１１）２つの受光素子が同じ程度に汚れているときは、前述した演算は省略してもよい。
（１２）２つの発光素子を同時にオンし、その前あるいは後に何れか１つの発光素子をオンした駆動方式の演算効果から画像濃度を算出しても良い。
（１３）正反射成分の現像器制御部への出力を行わなくても良い。
（１４）正反射成分を画像濃度制御部だけへ出力しても良く、あるいは現像器制御部と画像濃度制御部の両方へ出力しても良い。
【００３９】
【発明の効果】
以上説明した通り、本発明の画像濃度検知方法および装置、画像濃度制御方法および装置、および画像形成装置によると、画像からの正反射成分と拡散反射成分の両成分を受光する２つの受光素子の検出信号に所定の演算処理を施して画像の濃度を検出するようにしたので、２つの受光素子に汚れの差があっても高い精度で画像濃度を検出することができる。従って、トナー汚れ防止装置（トナー汚れ清掃装置）を設けなくとも、人間の色差認識限界値以下の画像再現性を得ることができ、かつ、構成の複雑化およびコストアップを抑えることができる。また、ノイズや迷光が侵入したとしても、２つの受光素子の検出信号に施される前述した所定の演算式によってある程度除去することができるので、信頼性の高い検出結果を得ることができる。
【図面の簡単な説明】
【図１】本発明の実施の形態における画像形成装置を示す説明図。
【図２】本発明の実施の形態における画像形成装置を示すブロック図。
【図３】本発明の実施の形態における画像形成装置の画像濃度検出部を示す説明図。
【図４】本発明の実施の形態における画像形成装置の画像濃度検出部の赤外ＬＥＤの駆動タイミングを示すタイミングチャート
【図５】本発明の実施の形態における画像形成装置の画像濃度検出部の濃度信号の演算値とトナー付着量の関係を示すグラフ。
【図６】従来の拡散／反射型濃度検知装置を示す説明図。
【図７】イエロー・マゼンダ・サイアンの各カラートナーの反射スペクトルを示す説明図。
【図８】従来の拡散／反射型濃度検知装置におけるトナー付着量と各受光素子出力および演算値の関係を示すグラフ。
【図９】従来の拡散／反射型濃度検知装置におけるイエロー・マゼンダ・サイアン・黒の各トナー付着量と各受光素子出力の関係を示すグラフ。
【図１０】従来の拡散／反射型濃度検知装置におけるトナー付着量と各受光素子出力の関係を示すグラフ。
【図１１】従来の拡散／反射型濃度検知装置における濃度信号の演算値とトナー付着量の関係を示すグラフ。
【符号の説明】
１， レーザ出力部
２， 感光体ドラム
３， スコロトロン帯電器
４， 用紙搬送路
５， 信号処理部
６， 現像器
７， 転写器
８， 定着器
１２，画像濃度検出部
２１，赤外ＬＥＤ
２２，ホトダイオード
２３，ホトダイオード
２４，赤外ＬＥＤ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image density detection method and apparatus, an image density control method and apparatus, and an image forming apparatus, and more particularly, to an image density detection method having a large dynamic range and preventing detection accuracy from being reduced by toner contamination. The present invention relates to an image forming apparatus, an image density control method and apparatus, and an image forming apparatus.
[0002]
[Prior art]
As a conventional image density detecting device, for example, JP-A-62-280869, JP-A-2-210370, JP-A-2-246984 (JP-B-7-95208), JP-A-3-209281 There are publications and the like.
[0003]
FIG. 6 shows a generalized configuration of the conventional image density detecting devices disclosed in these publications, and emits infrared light having a wavelength of around 950 nm to a toner image (for example, a color patch) 25 on the photosensitive drum 2. An infrared LED 21, a first photodiode 22 that receives specularly reflected light from the toner image 25, a second photodiode 23 that receives diffusely reflected light from the toner image 25, and blocks noise light from outside. A housing 26 accommodating the infrared LED 21 and the first and second photodiodes 22 and 23.
[0004]
FIG. 7 shows the reflection spectra of the yellow (Y), magenta (M), and cyan (C) color toners. The infrared light emitted by the infrared LED 21 and having a wavelength of around 950 nm is applied to the Y, M, and C color toners. Have the same reflectance.
[0005]
In the above configuration, when a Y, M, C or black (K) toner image 25 is formed on the photosensitive drum 2 and infrared light having a wavelength of about 950 nm is emitted from the infrared LED 21 to this toner image 25, The first photodiode 22 receives specularly reflected light, and the second photodiode 23 receives diffusely reflected light and generates an element output corresponding to the amount of received light.
[0006]
FIG. 8 shows the image density of the toner image 25, that is, the element output and the calculated value according to the toner adhesion amount. The diffuse reflected light component a based on the element output of the first photodiode 22 and the element output of the second photodiode 23 are shown. , And the calculated values (ab) of the specular reflection component a and the diffuse reflection component b calculated by a calculation circuit (not shown). The specular reflection component a tends to saturate when the toner adhesion amount increases, but the calculation result (ab) does not saturate even when the toner adhesion amount increases, so that the toner adhesion amount can be accurately determined with a large dynamic range. Can be detected.
[0007]
FIG. 9 shows the saturation characteristics of the element output based on the specularly reflected light of the Y, M, C, and K color toner images. As described above, when the toner adhesion amount increases in any of the color toner images, Since the element output of the specular reflection light is saturated, the dynamic range is reduced if the toner adhesion amount is detected based only on the specular reflection component.
[0008]
FIG. 10 shows the influence of contamination on the conventional image density detecting device shown in FIG. Since this image density detecting device detects the density of the unfixed toner image, if the light receiving surfaces of the photodiodes 22 and 23 become dirty with toner or the like, the element output of the photodiode 22 decreases from a to a ′, and The element output drops from b to b ′.
[0009]
FIG. 11 shows an image density detection error when the element outputs of the photodiodes 22 and 23 decrease. As is clear from the drawing, if the photodiodes 22 and 23 are both contaminated to the same degree, as shown by the curve (a′-b ′), the curve (a) when the photodiodes 22 and 23 are not contaminated to the same degree The result is almost the same as in -b) and an operation value having no error is obtained. However, when only one of the photodiodes 22 and 23 is contaminated, or when the degree of contamination is different, an operation value represented by a curve (ab ′) or (a′-b) is obtained. As a result, the calculated value of the toner adhesion amount has an error ± e. As long as there is this kind of error ± e, the target level of image reproducibility cannot be reduced to ΔE = 3 or less, which is the human color difference recognition limit value. Regarding the color difference recognition limit value, see COLOR Research and Application, Vol. 14 Number 3, June 1989, pages 139-151.
[0010]
On the other hand, as a conventional toner stain prevention device (toner stain cleaning device), for example, a device in which a light-receiving opening surface faces downward is disclosed in Japanese Utility Model Laid-Open No. 2-119270. Japanese Patent Application Laid-Open No. Hei 4-260077 discloses a structure in which a photodiode is housed, and Japanese Patent Application Laid-Open No. 5-43165 discloses a structure in which a photodiode can be retracted so that it can be cleaned without removing a photoreceptor.
[0011]
It is considered that the provision of the toner contamination preventing device in the conventional image density detecting device can solve the above-mentioned error ± e to some extent.
[0012]
[Problems to be solved by the invention]
However, according to the conventional image density detecting device, if a toner contamination preventing device is provided to prevent a difference in toner contamination between the two light receiving elements, an extra function is added, and the structure becomes complicated. Increases cost. Further, even if the toner contamination preventing device is provided, it is inevitable that a difference occurs in the cleaning degree between the two light receiving elements, so that the detection accuracy is reduced based on the above-mentioned error ± e, and is lower than the human color difference recognition limit value. Image reproducibility cannot be obtained.
[0013]
Therefore, an object of the present invention is to prevent a decrease in detection accuracy due to a difference in dirt between two light receiving elements and thereby to obtain an image density detection method and apparatus capable of obtaining image reproducibility below a human color difference recognition limit value. An object of the present invention is to provide an image density control method and apparatus, and an image forming apparatus.
[0014]
Another object of the present invention is to provide an image density detection method and apparatus, an image density control method and apparatus, and an image forming apparatus that can detect image density with high detection accuracy without providing a toner stain prevention apparatus. is there.
[0015]
Another object of the present invention is to reduce the complexity and cost of the structure, and to eliminate the influence of noise and stray light inevitable for light detection, an image density detection method and apparatus, an image density control method and apparatus, and An object of the present invention is to provide an image forming apparatus.
[0016]
[Means for Solving the Problems]
The present invention, in order to achieve the above object, illuminated by the first feature, the image density detection method for detecting the density of an image formed on an image bearing member, a first optical path or al light to the image as well as detected by the specular reflection light reflected from the image to the first receiving means, the diffuse reflection light reflected from the image and detected by the second light receiving means, said first optical path to the image The first light receiving unit detects diffuse reflected light reflected from the image by irradiating light from a different second optical path, and detects the regular reflected light reflected from the image by the second light receiving unit. An image density detection method is provided, wherein the density of the image is detected based on the regular reflection light and the diffuse reflection light detected by the first and second light receiving means .
[0017]
According to a second aspect of the present invention, there is provided an image density detecting apparatus for detecting the density of an image formed on an image carrier, wherein the image has a first optical path and a first optical path. First and second light irradiating means for irradiating light from a second light path different from the first light path, and receiving regular reflection light and diffuse reflection light reflected from the image based on the light from the first light path. First and second light receiving means for receiving diffuse reflection light and regular reflection light reflected from the image based on the light from the second optical path, and the regular reflection light of the first light receiving means Calculating means for calculating the density of the image based on the diffuse reflected light and the diffuse reflected light and the specular reflected light of the second light receiving means , wherein the first irradiating means and the first light receiving means Means are both normals of the image carrier. Are arranged at a first angle with respect to the normal, and the second irradiating means and the second light receiving means are provided on both sides of the normal with a second angle different from the first angle. Provided is an image density detection device characterized by being arranged at an angle .
[0018]
According to a third aspect of the present invention, there is provided an image density control method for detecting the density of an image formed on an image carrier and controlling the density according to a third feature. the irradiated the road or al light specularly reflected light reflected from the image as well as detected by the first light receiving means, the diffuse reflection light reflected from the image and detected by the second light receiving unit, to the image The first light receiving unit detects the diffuse reflection light reflected from the image by irradiating light from a second light path different from the first light path and detects the regular reflection light reflected from the image. 2, the density of the image is detected based on the regular reflection light and the diffuse reflection light detected by the first and second light reception means, and the density is detected based on the detected density. Before the image To provide an image density control method characterized by controlling the concentration to a predetermined concentration.
[0019]
According to a fourth aspect of the present invention, there is provided an image density control apparatus for detecting the density of an image formed on an image carrier by an image forming unit and controlling the density, according to a fourth feature. First and second light irradiating means for irradiating light from a first optical path and a second optical path different from the first optical path, and being reflected from the image based on the light from the first optical path First and second light receiving means for receiving regular reflection light and diffuse reflection light and receiving diffuse reflection light and regular reflection light reflected from the image based on the light from the second optical path; the specular reflection light and the diffuse reflection light of the first light-receiving means, and calculating means for calculating the density of the image based on the diffuse reflection light and the specularly reflected light of the second light receiving means, wherein The above calculated by the calculating means A control means for controlling the concentration to a predetermined concentration based on time, the first illumination means and the first light receiving means, first against the normal on both sides of the normal line of said image bearing member And the second irradiating means and the second light receiving means are arranged on both sides of the normal with a second angle different from the first angle . An image density control device is provided.
[0020]
According to a fifth aspect of the present invention, there is provided an image forming apparatus for detecting the density of an image formed on an image carrier and forming an image having a predetermined density on the image carrier, according to a fifth feature, Image forming means for forming the image on the image carrier, first and second light irradiating means for irradiating the image with light from a first optical path and a second optical path different from the first optical path, Diffuse reflection light that receives specular reflection light and diffuse reflection light reflected from the image based on the light from the first light path, and is reflected from the image based on the light from the second light path; And first and second light receiving means for receiving light and regular reflection light, the regular reflection light and the diffuse reflection light of the first light reception means, and the diffuse reflection light and the regular reflection of the second light reception means. Calculate the density of the image based on light And calculation means, wherein on the basis of the concentration calculated by the calculation means comprises a control means for controlling the concentration to the predetermined concentration, the first illumination means and the first light receiving means, said image bearing member Are arranged at a first angle with respect to the normal on both sides of the normal, and the second irradiating means and the second light receiving means are arranged on both sides of the normal with the first angle. Is provided with an image forming apparatus having a different second angle .
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an image density detection method and apparatus, an image density control method and apparatus, and an image forming apparatus of the present invention will be described in detail.
[0022]
FIG. 1 shows an embodiment of an image forming apparatus according to the present invention, in which a laser output unit 1 for emitting a laser beam corresponding to a recorded image to a charged photosensitive drum 2 and a memory such as a computer (not shown). A signal processing unit 5 that performs predetermined signal processing on the read image signal read from the CPU and outputs a recording image signal to the laser output unit 1; a scorotron charger 3 that charges the photosensitive drum 2; A developing unit 6 for developing the electrostatic latent image of the photoconductive drum 2 with toner, a toner image density detecting unit 12 for detecting a toner adhesion amount of the toner image on the photoconductive drum 2, and a toner on the photoconductive drum 2 The image forming apparatus includes a transfer unit 7 for transferring an image to a sheet conveyed to the sheet conveying path 4, a fixing unit 8 for fixing a transferred image on the sheet, and a cleaner 11 for removing residual toner on the photosensitive drum 2. The signal processing unit 5 may be configured to input a document reading signal generated by document scanning or a read image signal read from a memory that stores the document reading signal and perform signal processing.
[0023]
FIG. 2 shows a control system of the image forming apparatus shown in FIG. 1, and the same parts as those in FIG. 1 are denoted by the same reference numerals. , A density calculator 31 for outputting a corrected density signal containing no error, a developing device controller 32 for inputting the corrected density signal and outputting a control signal for controlling the developing conditions of the toner image, And a control signal from the developing unit control unit 32 to output a control signal for controlling the forming condition of the electrostatic latent image, and to rotate the developing roll of the developing unit 6 at a predetermined rotation speed. A developing roller drive motor 33 for rotating; a dispenser motor 34 for inputting a control signal from the developing device controller 32 and supplying a toner to the developing device 6 to supply a predetermined amount of toner; and an image density controller Control from 36 A light amount controller 36 for inputting a signal to control the amount of laser light emitted from the laser output unit 1 and a control signal from the image density control unit 36 to apply a controlled voltage to the grid of the scorotron charger 3 And a reference pattern signal generator 38 that receives a control signal from the image density controller 35 and generates a reference pattern signal for forming a 20 mm × 20 mm color patch on the photosensitive drum 2.
[0024]
FIG. 3 shows the toner image density detecting unit 12, which includes a first infrared LED 21 provided at an angle θ ₁ (0 <θ ₁ <90 °) with respect to a normal line of the photosensitive drum 2, and an angle theta ₁ with respect to the line, chromatic and first photodiode 22 provided on the opposite side of the first infrared LED 21, the angle theta ₂ with respect to the normal to _{(0 <θ 2 <90 °} ) A second infrared LED 24 having an angle θ ₂ with respect to the normal line and a second photodiode 23 provided on the opposite side of the second infrared LED 24; For example, an aluminum housing 26 for accommodating the infrared LEDs 21 and 24 and the first and second photodiodes 22 and 23 and preventing intrusion of external noise light and heat rays (infrared light) of the fixing unit 8 is provided. are doing. A color patch 25 is formed on the photosensitive drum 2.
[0025]
The operation of the above configuration will be described below.
[0026]
The input read-out image signal is subjected to appropriate signal processing in a signal processing unit 5, converted into a recorded image signal, input to the laser output unit 1, and modulates a laser beam. In this way, the laser beam modulated by the recording image signal is radiated to the photosensitive drum 2 in a raster manner.
[0027]
On the other hand, the photosensitive drum 2 is uniformly charged by the scorotron charger 3, and when irradiated with laser light, an electrostatic latent image corresponding to a recording image signal is formed on the surface thereof. Next, the electrostatic latent image is developed with toner by the developing unit 6, the toner image is transferred onto a sheet (not shown) by the transfer unit 7, and fixed by the fixing unit 8. Thereafter, the photosensitive drum 2 is cleaned by the cleaner 11, and one image forming operation is completed.
[0028]
In the above-described image forming apparatus, a reference pattern signal is transmitted from the reference pattern signal generator 38 to the laser output unit 1 in accordance with an instruction from the image density control unit 35, and a toner image 25 of the reference pattern is formed on the photosensitive drum 2. . For example, the toner image 25 is formed so as to have 60% color toner in an area ratio of 20 mm × 20 mm. Next, the toner image density detector 12 measures the density of the toner image 25 of the reference pattern.
[0029]
FIG. 4 shows the drive timing of the toner image density detection unit 12. The first infrared LED 21 and the second infrared LED 24 are turned on alternately, and each emits infrared light having a wavelength around 950 nm. When the first infrared LED 21 is turned on, the first photodiode 22 receives regular reflection light from the toner image 25, and the second photodiode 23 receives diffuse reflection light. On the other hand, when the second infrared LED 24 is turned on, the second photodiode 23 receives the regular reflection light from the toner image 25, and the first photodiode 22 receives the diffuse reflection light. In this manner, the first and second photodiodes 22 and 23 output density signals based on the amount of received light to the density calculation unit 31, respectively.
[0030]
FIG. 5 shows the content of the calculation by the density calculation unit 31, where (ab ′) is a density signal a based on a regular reflection component whose level is not reduced by being received through a light-receiving surface free of toner contamination, The difference from the density signal b 'based on the diffuse reflection component, which is caused by the light receiving through the light receiving surface contaminated by the toner, and the level is reduced. (A'-b) is the light receiving through the light receiving surface contaminated by the toner. The difference between the density signal a ′ based on the specular reflection component whose level has been reduced by the operation and the density signal b based on the diffuse reflection component whose level has not been reduced due to the light being received through the light-receiving surface free from toner contamination. It is.
[0031]
As described above, when the first infrared LED 21 is turned on, the density signal a, b ′ or a ′, b is output from the toner image density detector 12 to the density calculator 31, and the second infrared LED 24 Is turned on, density signals a 'and b or a and b' are output.
[0032]
The density calculator 31 stores the input density signals a, a ', b, and b' in a memory, and then calculates and corrects c = {(ab ') + (a'-b)} / 2. The density signal c is output to the developing unit control unit 32 and the image density control unit 35, and the density signal a based on the regular reflection component in which the level does not decrease is output to the developing unit control unit 32.
[0033]
The developing device controller 32 has the following table as a density target value based on the regular reflection component of the 60% color patch described above.
[Table 1]

[0034]
When the toner image 25 is formed of yellow toner, the developing device controller 32 compares the density signal a with 33% of the target value, and generates a control signal in consideration of the corrected density signal c to generate a developing roller. The number of rotations of the drive motor 33 and the toner supply dispenser motor 34 is controlled. As a result, the toner adhesion amount is controlled to a predetermined value.
[0035]
When the correction density signal c is input, the image density control unit 35 controls the grid power supply 37 of the scorotron charger 3 and the light amount controller 36 of the laser output unit 1 to emit the grid voltage of the scorotron charger 3 and the laser output unit 1. The amount of laser light to be applied is set to a predetermined value. Thereby, the contrast ratio of the electrostatic latent image is controlled to a predetermined value.
[0036]
In this way, a high-quality recorded image having a predetermined image density can be obtained.
[0037]
Here, the relationship between the lighting of the first and second infrared LEDs 21 and 24 and the outputs of the first and second photodiodes 22 and 23 is summarized as follows.
[Table 2]

[0038]
As described above, the image forming apparatus of the present invention has been described based on the embodiment, but the present invention is not limited to this embodiment, and for example, the following modifications are possible.
(1) The toner image density detection may be performed using a normal output image without forming a color patch for reading.
(2) At least one of the operation amounts of the charge amount, the exposure amount, the developing bias, the rotation speed of the developing roll, and the toner supply coefficient may be controlled, but other operation amounts may be used. Further, the present invention can be applied to control other than image density control or toner supply control.
(3) The toner density signal may be used, for example, for determination, warning display, and the like.
(4) The density of a transferred image on paper, a toner image on an intermediate transfer member, or an image after fixing may be detected.
(5) The arrangement angle of the light emitting means and the light receiving means may be θ ₁ > θ ₂ . Further, the second photodiode 23 is arranged on the same side as the first infrared LED 21 with respect to the normal line of the photoconductor surface, but is opposite to the first infrared LED 21 with respect to the normal line of the photoconductor surface. May be on the side.
(6) As the light emitting means, for example, a halogen lamp, a laser diode, or the like can be used. As the light receiving means, for example, a phototube, a photomultiplier, a photoconductor, or the like can be used.
(7) The light receiving and emitting means may be provided with a condensing optical system.
(8) The density calculation is not limited to the above-described subtraction, and the following division and other calculations may be used.
(Equation 1)

(9) The following arithmetic expression may be used instead of the arithmetic expression {(ab ′) + (a′−b)} / 2.
[Table 3]

(10) The light emitting and receiving elements may be respectively or one of them, and may be moved between two positions so as to receive the regular reflection component and the diffuse reflection component.
(11) When the two light receiving elements are contaminated to the same extent, the above-described calculation may be omitted.
(12) The image density may be calculated from the calculation effect of the driving method in which two light emitting elements are turned on at the same time and one of the light emitting elements is turned on before or after that.
(13) It is not necessary to output the regular reflection component to the developing device controller.
(14) The specular reflection component may be output only to the image density controller, or may be output to both the developing device controller and the image density controller.
[0039]
【The invention's effect】
As described above, according to the image density detection method and apparatus, the image density control method and apparatus, and the image forming apparatus of the present invention, the two light receiving elements that receive both the regular reflection component and the diffuse reflection component from the image are used. Since a predetermined arithmetic processing is performed on the detection signal to detect the density of the image, the image density can be detected with high accuracy even if there is a difference between the two light receiving elements. Therefore, it is possible to obtain image reproducibility equal to or less than the human color difference recognition limit value without providing a toner stain prevention device (toner stain cleaning device), and it is possible to suppress a complicated configuration and an increase in cost. Further, even if noise or stray light enters, it can be removed to some extent by the above-described predetermined arithmetic expression applied to the detection signals of the two light receiving elements, so that a highly reliable detection result can be obtained.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram illustrating an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating an image forming apparatus according to the embodiment of the present invention.
FIG. 3 is an explanatory diagram illustrating an image density detection unit of the image forming apparatus according to the embodiment of the present invention.
FIG. 4 is a timing chart showing a drive timing of an infrared LED of an image density detecting unit of the image forming apparatus according to the embodiment of the present invention; 5 is a graph showing a relationship between a calculated value of a density signal and a toner adhesion amount.
FIG. 6 is an explanatory view showing a conventional diffusion / reflection type density detecting device.
FIG. 7 is an explanatory diagram showing reflection spectra of yellow, magenta, and cyan color toners.
FIG. 8 is a graph showing the relationship between the toner adhesion amount, the output of each light receiving element, and a calculated value in a conventional diffusion / reflection type density detecting device.
FIG. 9 is a graph showing the relationship between the amounts of adhered toner of yellow, magenta, cyan, and black and the output of each light receiving element in a conventional diffuse / reflective density detecting device.
FIG. 10 is a graph showing the relationship between the toner adhesion amount and the output of each light receiving element in a conventional diffusion / reflection type density detecting device.
FIG. 11 is a graph showing a relationship between a calculated value of a density signal and a toner adhesion amount in a conventional diffusion / reflection type density detection device.
[Explanation of symbols]
1, laser output unit 2, photoreceptor drum 3, scorotron charger 4, paper transport path 5, signal processing unit 6, developing unit 7, transfer unit 8, fixing unit 12, image density detecting unit 21, infrared LED
22, photodiode 23, photodiode 24, infrared LED

Claims (15)

In an image density detection method for detecting the density of an image formed on an image carrier,
Thereby detecting the specularly reflected light reflected from the first of the image by irradiating the optical path or al light on the image by the first light receiving means, the diffuse reflection light reflected from the image second light receiving means Detected by
The image is irradiated with light from a second optical path different from the first optical path, and diffused reflected light reflected from the image is detected by the first light receiving unit, and regular reflected light reflected from the image is detected. Is detected by the second light receiving means,
An image density detection method, comprising: detecting a density of the image based on the regular reflection light and the diffuse reflection light detected by the first and second light receiving units. The detection of the density of the image includes a first operation of comparing the specular reflection light of the light from the first optical path and the diffuse reflection light, and the specular reflection of the light from the second optical path. 2. The image density detection method according to claim 1, wherein the second operation is performed by comparing the result of the first and second operations with the diffused reflected light, and the third operation is performed by comparing the results of the first and second operations. 3. The image density detection method according to claim 2, wherein the comparison between the first and second calculations is a subtraction for calculating a difference, and the third calculation calculates an average value of the differences. 3. The image density detecting method according to claim 2, wherein the comparison between the first and second operations is a division, and the third operation performs a predetermined operation on a result of the division. In an image density detection device for detecting the density of an image formed on an image carrier,
First and second light irradiation means for irradiating the image with light from a first optical path and a second optical path different from the first optical path;
Diffuse reflection light that receives specular reflection light and diffuse reflection light reflected from the image based on the light from the first light path, and is reflected from the image based on the light from the second light path; And first and second light receiving means for receiving regular reflection light,
Calculating means for calculating the density of the image based on the specularly reflected light and the diffusely reflected light of the first light receiving means and the diffusely reflected light and the specularly reflected light of the second light receiving means ;
The first irradiating unit and the first light receiving unit are arranged on both sides of a normal line of the image carrier at a first angle with respect to the normal line,
The image density detecting device according to claim 1, wherein the second irradiating unit and the second light receiving unit are arranged at both sides of the normal line at a second angle different from the first angle . The calculating means is configured to perform a first calculation of comparing the specularly reflected light received by the first light receiving means with the diffusely reflected light received by the second light receiving means; A structure for executing a second operation for comparing the diffuse reflection light with the regular reflection light received by the second light receiving means and a third operation for comparing the results of the first and second operations. 5. The image density detecting device according to 5. The calculating means calculates a difference by performing subtraction between the specular reflection light and the diffuse reflection light as a comparison between the first and second calculations, and calculates the first and second values as a comparison between the third calculation. 7. The image density detecting device according to claim 6, wherein an average value of the difference in the calculation of 2 is calculated. The calculating means calculates a division result by performing a division between the specular reflection light and the diffused light as a comparison between the first and second calculations, and calculates the first and second calculations as a comparison of the third calculation. 7. The image density detection device according to claim 6, wherein a predetermined operation is performed on the division result in the operation of 2. An image density control method for detecting the density of an image formed on an image carrier and controlling the density,
Thereby detecting the specularly reflected light reflected from the first of the image by irradiating the optical path or al light on the image by the first light receiving means, the diffuse reflection light reflected from the image second light receiving means Detected by
The image is irradiated with light from a second optical path different from the first optical path and diffused reflected light reflected from the image is detected by the first light receiving unit, and regular reflected light reflected from the image is detected. Is detected by the second light receiving means,
Detecting a density of the image based on the regular reflection light and the diffuse reflection light detected by the first and second light receiving units;
An image density control method, wherein the density of the image is controlled to a predetermined density based on the detected density. The formation of the image on the image carrier is performed by charging a photoconductor, forming an electrostatic latent image based on exposure of the photoconductor according to the image, and developing the electrostatic latent image into a toner image. I,
10. The image density detection method according to claim 9, wherein the control of the predetermined density is performed by adjusting at least one of the charge amount of the charging, the light amount of the exposure, the developing voltage of the development, and the toner supply amount. In an image density control device that detects the density of an image formed on an image carrier by an image forming unit and controls the density,
First and second light irradiation means for irradiating the image with light from a first optical path and a second optical path different from the first optical path;
Diffuse reflection light that receives specular reflection light and diffuse reflection light reflected from the image based on the light from the first light path, and is reflected from the image based on the light from the second light path; And first and second light receiving means for receiving regular reflection light,
Calculating means for calculating the specular reflection light and the diffuse reflection light, and the density of the image based on the diffuse reflection light and the specularly reflected light of the second light receiving means of said first light receiving means,
Control means for controlling the density to a predetermined density based on the density calculated by the calculation means ,
The first irradiating unit and the first light receiving unit are arranged on both sides of a normal line of the image carrier at a first angle with respect to the normal line,
An image density control device according to claim 1, wherein said second irradiating means and said second light receiving means are arranged at both sides of said normal line at a second angle different from said first angle . The image forming unit includes a charging unit that charges a photoconductor, an exposure unit that exposes the charged photoconductor according to the image to form an electrostatic latent image, and a developing unit that develops the electrostatic latent image. Having developing means for forming a toner image,
The image density control device according to claim 11, wherein the control unit controls at least one image forming condition of the charging unit, the exposing unit, and the developing unit. In an image forming apparatus for detecting the density of an image formed on an image carrier and forming an image of a predetermined density on the image carrier,
Image forming means for forming the image on the image carrier,
First and second light irradiation means for irradiating the image with light from a first optical path and a second optical path different from the first optical path;
Diffuse reflection light that receives specular reflection light and diffuse reflection light reflected from the image based on the light from the first light path, and is reflected from the image based on the light from the second light path; And first and second light receiving means for receiving regular reflection light,
Calculating means for calculating the density of the image based on the specular reflected light and the diffuse reflected light of the first light receiving means, and the diffuse reflected light and the specular reflected light of the second light receiving means;
Control means for controlling the density to the predetermined density based on the density calculated by the calculation means ,
The first irradiating unit and the first light receiving unit are arranged on both sides of a normal line of the image carrier at a first angle with respect to the normal line,
The image forming apparatus, wherein the second irradiating unit and the second light receiving unit are arranged on both sides of the normal line at a second angle different from the first angle . The image forming unit includes a charging unit that charges a photoconductor, an exposure unit that exposes the charged photoconductor according to the image to form an electrostatic latent image, and a developing unit that develops the electrostatic latent image. Having developing means for forming a toner image,
14. The image forming apparatus according to claim 13, wherein the control unit controls at least one image forming condition of the charging unit, the exposing unit, and the developing unit. The charging unit is a scorotron charger having a grid electrode to which a predetermined grid voltage is applied from a grid power supply,
The exposure unit has a laser output unit that emits laser light corresponding to the image, and a light amount controller that controls the light amount of the laser light,
The developing unit has a developing roll drive motor that drives a developing roll, and a dispenser motor that drives a toner supply dispenser,
15. The image forming apparatus according to claim 14, wherein the control unit controls at least one of the grid power supply, the light amount controller, the developing roll drive motor, and the dispenser motor to bring the image to the predetermined density. 16. apparatus.

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