JP3576577B2 - Image density detection device - Google Patents

Description

で表される。ただし、Ｖ_ｍａｘ は感光体へ入射した発光素子（ＬＥＤランプ）１の光がすべて反射して受光素子（反射型光センサ）２に全部捕らえられた時のセンサ出力を表し、Ｖｃは原画濃度ｃ（複写濃度ｎ）の時のセンサ出力を表し、そしてＶｘは各トナー濃度パッチの濃度検知に基づくセンサ出力を表している。
【００４２】
図６から図８までの実施例では、ゲインｂをゲインａよりも大きくした場合について述べたが、ゲインｂをゲインａよりも小さくする場合もあり得る。その場合には、複写濃度に関するデータの取捨選択が図７とは逆になり、従って、γカーブの合成も複写濃度ｎ以下の部分が合成されることになる。この時のｎｘの変換は、
【００４３】
【数２】

【００４４】
【発明の効果】
以上に記述した構成を有する本発明によれば、画像パターンの濃度検知測定におけるセンサの出力レベルを正確かつ容易に複写濃度に対応（一致）させることができるので、所望の画像制御が高い精度で達成され得る。さらに、感光体のフレ量に影響されることなく、低濃度から高濃度までの広範囲にわたって確実な濃度検知が容易に達成される。
【図面の簡単な説明】
【図１】本発明の第１実施例を示すブロック図である。
【図２】本発明の第２実施例を示すブロック図である。
【図３】画像パターンの濃度検知測定の１例を示し、（ａ）では複数このトナ−濃度パッチからなる画像パターンが示され、（ｂ）では各トナー濃度パッチの検知レベルが示され、そして（ｃ）では（ｂ）に示された検知レベルに対応する複写濃度が示される。
【図４】本発明の第３実施例を示すブロック図である。
【図５】本発明の第４実施例を示すブロック図である。
【図６】画像パターンの濃度検知測定のもう１つの例を示し、（ａ）では所定のゲインを用いた測定が、（ｂ）では（ａ）におけるゲインよりも大きいゲインを用いた測定が示される。
【図７】図６における２回の濃度検知測定に関連して求められたそれぞれのＯＤ−ＣＤ特性（γカーブ）を示すグラフである。
【図８】図７に示された２つの、γカーブの合成作業を示す説明的グラフである。
【符号の説明】
１ 発光素子（ＬＥＤランプ）
２ 受光素子（反射型光センサ）
３ Ｉ／Ｖ変換器
４ 増幅および演算部
５ 対数変換部
５ａ 対数変換部
５ｂ 対数変換部
６ Ａ／Ｄ変換器
７ メモリ
８ 平均化処理部
９ 複写濃度判定部
Ｖｘ 検知レベル
ｄｘ デジタル値
ｎｘ 複写濃度
ａ ゲイン
ｂ ゲイン
ｐ_１ 〜ｐ_ｎ トナー濃度パッチ
Ｐ 画像パターン
ｉ 信号（電流値）
ｖ 電圧信号[0001]
[Industrial applications]
The present invention is directed to an image forming apparatus such as a copying machine, a facsimile, and a printer in which a developing material (hereinafter, simply referred to as a toner) is attached to a photoreceptor surface to form an image. The present invention relates to an image density detecting device for detecting the density of a toner image (toner density patch), and more particularly to detecting a toner density patch on a photoreceptor to accurately determine a reflection density (corresponding to a copy density when transferred onto paper). The present invention relates to an image density detecting device in a digital image forming apparatus capable of detecting an image density.
[0002]
[Prior art]
In order to read a document image, reflected light of irradiation light directed from the exposure lamp toward the document is once read by a scanning image input device (CCD), and is controlled to an appropriate light amount in an image processing unit based on information in the CCD. In a digital image forming apparatus configured to expose a photoconductor surface with a laser beam, a conventional image density detection device uses a LED lamp or the like to emit light (near red) to a toner density patch formed on the photoconductor. External light) is emitted, and the output level (voltage value) of a reflection type optical sensor (for example, a phototransistor or the like) by the reflected light from each toner density patch is sent to the next system for image control.
[0003]
In an image forming apparatus that forms an image on a drum by changing laser irradiation conditions in accordance with density data of a document read by a CCD, the image density on the drum is compared with the density data of the document. Are different from each other, it is possible to control so that the two are always equal by changing the irradiation condition of the laser beam.
[0004]
[Problems to be solved by the invention]
However, in the conventional image density detecting device, it is impossible to make the output level at which the toner density patch formed on the photoreceptor is detected correspond to the copy density after being transferred onto the paper. This is particularly noticeable in a toner density patch in a low density area. This is because the reflected light from the toner density patch in the low density area on the photoconductor contains more reflected light from the drum surface, and the sensor output due to this reflected light is smaller than the sensor output due to the reflected light from the transfer paper surface. Is also expensive.
[0005]
Further, the conventional image density detection is performed on a plurality of toner density patches formed on a photoreceptor under one kind of detection condition and by only one measurement. For this reason, it is difficult to determine the density difference especially in the high density area and the low density area. In addition, accurate detection is not possible because of the influence of the amount of deflection due to the curvature of the photoconductor. In order to solve this problem, a method of switching the amplification factor while measuring in one measurement, or switching the amplification factor at a predetermined position has been considered, but the former method achieves this. The device for the measurement is complicated, and the latter may cause a measurement error.
[0006]
In addition, the individual toner density patches formed on the photoreceptor do not have uniform densities on one side, and it is possible to obtain an accurate density by measuring only one point in the conventional image density detection method. Have difficulty.
[0007]
The present invention has been made in view of the above-described circumstances in the related art, and has as its object to minimize the influence of the amount of deflection due to the curvature of the surface of the photoreceptor, as well as to achieve high density regions and low density regions. An object of the present invention is to provide an image density detecting device capable of reliably detecting a density difference in an area.
[0021]
To achieve the above object, according to a first aspect of the present invention, a plurality of toner density patches having different density gradations formed on a photoreceptor so as to have a plurality of density gradations are reflected light. In the image density detection apparatus for detecting using an image sensor, the detection is repeatedly performed at least twice or more, and a process including a logarithmic conversion process is performed for each detection level obtained by the detection. Is provided.
[0022]
According to a second aspect of the present invention, in the detection device according to the first aspect, the detection of a plurality of sets of the image patterns is performed under different detection conditions for each set of the image patterns. An image density detecting device is provided.
[0023]
According to a third aspect of the present invention, there is provided the detection device according to the second aspect, wherein each of the image patterns is obtained by detection performed under different detection conditions, and thereafter, a logarithmic conversion process is performed. A plurality of output values corresponding to the copy densities by selecting a plurality of output values with a certain density as a boundary, and further comprising processing means for synthesizing the remaining output values so as to be continuous with each other. The present invention provides a device for detecting an image density.
[0024]
[Action]
Irradiation light from the light emitting element (LED lamp) is sequentially reflected from each toner density patch formed on the photoreceptor and received by the light receiving element (reflection type optical sensor), and the detection level (predetermined current value) from the light receiving element Are sequentially output. After these detection levels are converted into voltage values by I / V (current / voltage) conversion, they are sequentially subjected to amplification and arithmetic processing. Thereafter, each output value is subjected to logarithmic conversion processing, and each of the detection levels can be sent to the next system as an output value corresponding to (coincident with) the copy density after transfer.
[0025]
In the logarithmic conversion processing, the output value subjected to the amplification and the arithmetic processing is digitized by A / D (analog / digital) conversion, and the digital value is used as an address of a memory in which various logarithmic values are stored in advance. Done easily.
[0026]
Further, in order to achieve more accurate density detection, each of the plurality of toner density patches formed on the photoreceptor is detected at least twice or more, and the plurality of toner density patches obtained by the detection are detected. The detection level undergoes an averaging process.
[0027]
Further, in order to increase the detection accuracy in the high density area and the low density area of the toner density patch, each of the toner density patches is formed of the plurality of toner density patches, and is formed in two or more sets on the photosensitive member. By performing density detection on image patterns under different detection conditions (gains), a plurality of detection levels with different gains can be obtained. Subsequently, these detection levels are converted into a plurality of output values each corresponding to the copy density. Then, these output values are selected on the basis of a certain density, and are synthesized so that the remaining output values are continuous with each other.
[0028]
【Example】
Some exemplary embodiments of the present invention will be described with reference to the accompanying drawings.
Figure 1 is a block diagram of a first embodiment of the present invention comprises a plurality of toner density patch p ₁ ~p _n formed on the surface of the photoreceptor D, and a plurality of stages from a low concentration to a high concentration concentration floors Light (near-infrared light) is emitted from the light emitting element 1 such as an LED lamp toward the image pattern P having a tone. This irradiation light is reflected by each toner density patch, and the respective reflected light is detected by the light receiving element 2 such as a reflection type optical sensor (phototransistor).
[0029]
The light receiving element 2 outputs a signal (current value) i according to the intensity of the received reflected light. Subsequently, the signal i is passed through an I / V (current / voltage) converter 3 and converted into a voltage signal v, which is further changed to a predetermined detection level Vx by the amplification and operation unit 4. In the conventional image density detection, as described above, this detection level Vx is output as it is to the next system. However, in the present invention, the detection level Vx is set to achieve more accurate image control as easily as possible. The detection level Vx is converted to a copy density nx through a logarithmic converter 5 so that Vx corresponds to (coincides with) the density (copy density) on the paper after transfer, and is output to the next system.
[0030]
The logarithmic conversion of the detection level Vx may be performed by sequentially calculating in the logarithmic converter 5, but can be easily performed by the second embodiment of the present invention as shown in the block diagram of FIG. That is, the logarithmic converter 5a stores in the memory 7 various logarithmic values corresponding to the respective detection levels in advance as a conversion table, and A / D (analog / digital) conversion for outputting an address signal to the memory 7. The detection level Vx output from the amplification and operation unit 4 is converted into a digital value via the A / D converter 6 and used as an address signal of the memory 7. Therefore, according to this modification, every time the detection level Vx is output, the address signal corresponding to each detection level is sequentially output from the A / D converter 6, and the copy density nx is easily stored in the memory 7 each time. Is output. Incidentally, the copy density nx is represented by _{nx = e · log (Vx /} V max). Here, e is a constant, and V _max is a sensor output when the total reflection light from the photoconductor D of the light emitting element 1 is captured by the light receiving element 2.
[0031]
FIG. 3 shows an example of an image pattern composed of three types of toner density patches formed on a photoconductor (a), a graph (b) showing a detection level Vx for this image pattern, and a copy density corresponding to each detection level. The relationship of the graph (c) showing nx is shown. That is, when the density detection is performed on the image pattern shown in FIG. 3A, as is apparent from the graph of FIG. Accordingly, the detection level varies even within the same toner density patch, and the detection level is unstable particularly at the edge portions of the toner density patches adjacent to each other.
[0032]
Therefore, in order to determine an accurate density detection for one density patches, as reflected light from different locations relative to one concentration patch is received by the light receiving element 2, made of at least two or more detection Therefore, it is necessary to perform an averaging process on the obtained plurality of detection levels. Further, since the influence of the above-mentioned blur amount is greater for a high-density toner density patch, in an image pattern composed of a plurality of toner density patches formed on a photoreceptor, the higher the density of a toner density patch in a high-density area is, the more the patch becomes The number is increased and the gradation is moderated.
[0033]
The graph of FIG. 3C shows the copy density when the averaging process is not performed on the detection level (shown by a white circle) and the copy density when the averaging process is performed (shown by a black circle). ing. As is apparent from this graph, when the averaging process is not performed on the detection level, the copy density to be sent to the next system also has a variation in the detection level.
[0034]
FIG. 4 is a block diagram of a third embodiment of the present invention in which the logarithmic conversion unit 5b includes an averaging unit 8 for a plurality of detection levels obtained by performing a plurality of density detections on a toner density patch . According to FIG. 4, a plurality of detection levels output from the amplification and operation unit 4 are passed through an A / D converter 6 and converted into digital values dx, respectively. , And the averaged digital value is used as an address signal of the conversion table stored in the memory 7. As a result, variations in the detection level are corrected, and accurate density detection of the toner density patch is achieved.
[0035]
An example of the detection level averaging process in the present invention is performed as follows. That is, when each toner density patch passes through the light receiving element 2 as a sensor at a speed of several tens to several hundred meters / second, the detection level A / D is detected at a speed interval of several to tens of meters / second. The conversion is performed, so that several to dozens of digital values are sent to the averaging unit 8 for each toner density patch. The averaging unit 8 calculates an average value of all the digital values, or calculates a part of the average values.
[0036]
In the density detection, there remains a problem that cannot be solved by the third embodiment. That is, if an image pattern having a wide range of density gradations from low density to high density is to be detected with one type of gain (amplification factor), the detection level of the low density area is too small or the detection level of the high density area is too low. As the level saturates, the concentration of at least one of these regions is not accurately detected. A density detecting method and a detecting device for solving this problem are a fourth embodiment of the present invention described below with reference to FIGS. The fourth embodiment shown in the block diagram of FIG. 5 is provided with a copy density judging unit 9 after the logarithmic conversion unit 5, which detects a density detecting part whose numerical value is not clear, and is suitable for that part. The logarithmic conversion is performed again with the gain, the previous density detection result and the subsequent density detection result are selectively selected, and the clear density results both before and after are combined. As a result, clear and accurate copy density can be output to the next system.
[0037]
The operation of the copy density determining section 9 will be described below with reference to FIGS. A graph (a) on the left side of FIG. 6 shows a detection level VX when an image pattern p formed of a plurality of toner density patches p1 to pn formed on the photoconductor D is first subjected to density detection measurement using the gain a. It is. In the graph (a), the detection level VX relating to the high-density area A has a small gain, so the numerical value is not clear, and the density difference between the toner density patches is unknown. The copy density determination unit detects unclear detection levels in these high-density areas, and instructs the logarithmic conversion unit 5 to perform density detection measurement on the same image pattern P with the gain set to b (where b> a ). Instruct. The detection level VX obtained by using the large gain b is shown in a graph (b) on the right side of FIG. In the graph (b), the detection level for the low-density area B is saturated due to the large gain used, and accurate density detection is impossible. On the other hand, the graph (a) is not clear. In the high density area, the density difference is clearly shown for each toner density patch, and the numerical value of each detection level is also accurately detected. The operation of synthesizing accurate and clear measurement results obtained by these two concentration detection measurements will be described with reference to FIGS.
[0038]
In the above description, one image pattern P is used for the density detection twice by changing the gain . However, at least two or more identical image patterns are formed on the photosensitive member, and the plurality of image patterns are formed. However, the same result can be obtained even if the gain is switched each time and continuous measurement is performed using different gains.
[0039]
FIG. 7 shows OD-CD characteristics (generally called a γ curve in relation to the original image density OD and the copy density CD) created from the results of the two density detection measurements shown in FIG. . In FIG. 7, a γ curve based on the density detection measurement using the gain a is indicated by a solid line, and a γ curve based on the density detection measurement using the gain b (b> a) is indicated by a dashed line. As is apparent from FIG. 7, the density difference in the high density region surrounded by the thin dotted line is not clear in the γ curve of the gain a, while the low density region surrounded by the thin dotted line in the γ curve of the gain b. Is not clear. Therefore, two γ curves are selected by setting a specific copy density n (for example, n = 1, and the original image density at this time as c) as a threshold level. That is, in FIG. 7, data of the copy density n or less in which the density difference is clear is left in the γ curve of the gain a, while the copy density n or more in which the density difference is clearly shown in the γ curve of the gain b. Data is left.
[0040]
FIG. 8 shows the operation of synthesizing the remaining portions of the two .gamma. Curves selected in FIG. Thick dotted lines indicate the discarded portions of each of the two gamma curves. The remaining part of the γ curve of the gain b is converted as follows and combined with the remaining part of the γ curve of the gain a. Assuming that the copy density of a portion exceeding the copy density n is nx,
[0041]
(Equation 1)

It is represented by Here, V _max represents the sensor output when all the light of the light emitting element (LED lamp) 1 incident on the photoconductor is reflected and captured by the light receiving element (reflection type optical sensor) 2, and Vc is the original image density c Vx represents the sensor output based on the density detection of each toner density patch.
[0042]
In the embodiments of FIGS. 6 to 8, the case where the gain b is larger than the gain a has been described, but the gain b may be smaller than the gain a. In this case, the selection of the data relating to the copy density is the reverse of that in FIG. 7, and therefore, in the synthesis of the γ-curve, the portion having the copy density n or less is also synthesized. The conversion of nx at this time is:
[0043]
(Equation 2)

[0044]
【The invention's effect】
According to the present invention having the above-described configuration, the output level of the sensor in the density detection measurement of the image pattern can accurately and easily correspond (coincide) with the copy density, so that desired image control can be performed with high accuracy. Can be achieved. Furthermore, reliable density detection can be easily achieved over a wide range from low density to high density without being affected by the amount of deflection of the photoconductor.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first embodiment of the present invention.
FIG. 2 is a block diagram showing a second embodiment of the present invention.
3A and 3B show an example of density detection measurement of an image pattern, FIG. 3A shows an image pattern including a plurality of toner density patches, FIG. 3B shows a detection level of each toner density patch, In (c), the copy density corresponding to the detection level shown in (b) is shown.
FIG. 4 is a block diagram showing a third embodiment of the present invention.
FIG. 5 is a block diagram showing a fourth embodiment of the present invention.
6A and 6B show another example of density detection measurement of an image pattern, wherein FIG. 6A shows a measurement using a predetermined gain, and FIG. 6B shows a measurement using a gain larger than the gain in FIG. It is.
FIG. 7 is a graph showing OD-CD characteristics (γ curves) obtained in association with two density detection measurements in FIG.
FIG. 8 is an explanatory graph showing an operation of synthesizing the two γ curves shown in FIG. 7;
[Explanation of symbols]
1 light emitting element (LED lamp)
2 Light receiving element (reflective optical sensor)
3 I / V converter 4 Amplification and operation unit 5 Logarithmic conversion unit 5a Logarithmic conversion unit 5b Logarithmic conversion unit 6 A / D converter 7 Memory 8 Averaging processing unit 9 Copy density determination unit Vx Detection level dx Digital value nx Copy density a gain b gains p _{1 to pn} toner density patch P image pattern i signal (current value)
v voltage signal

Claims (3)

In an image density detection device that detects an image pattern formed of a plurality of toner density patches having different density gradations formed on a photoconductor using a reflection type optical sensor,
One image pattern is formed, or the same plurality of image patterns are formed, and the detection is performed under a plurality of different detection conditions when forming one image pattern, and the same plurality of image patterns are formed. An image density detecting apparatus, wherein when forming a plurality of image patterns, detection is performed under different detection conditions for each image pattern. A plurality of output values obtained by the above-described detection performed on the image pattern under different detection conditions, and then subjected to logarithmic conversion processing and corresponding to the copy density, are respectively selected at a certain density as a boundary. 2. The apparatus according to claim 1, further comprising processing means for combining the remaining output values so as to be continuous with each other. The image density detecting device according to claim 1, wherein the detection condition is a gain.

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