JP5262671B2 - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce toner consumption and image quality adjustment time in an image forming apparatus configured to calibrate an optical sensor based on a detection value of a gray-scale pattern composed of formed toner patches by changing, when the calibration of the optical sensor is not needed, the number of gray-scale patterns to be formed. <P>SOLUTION: The image density control device is configured, for determining an imaging condition, to detect a gray-scale pattern composed of a plurality of toner patches different in amount of adhesion continuously formed on a detection object by an optical detection means disposed in a position facing the detection object surface, perform calibration of the optical detection means based on the value of output voltage of the optical detection means obtained from the detection result, and calculate the amount of toner adhesion from the calculation result. The imaging condition of the gray-scale pattern is variable. The image density control device includes a toner patch quantity change means which changes the number of toner patches constituting the gray-scale pattern when it is determined that the calibration of the optical detection means is not needed. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an image density control apparatus in an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile, an image density control method used therefor, and an image forming apparatus using the image density control method.

Conventionally, image forming apparatuses such as electrophotographic copying machines and laser beam printers have a problem in that the density of the formed image changes with changes in usage environment (temperature / humidity) and changes over time. .
Therefore, in order to always obtain a stable image density, a gradation pattern for density detection is created on an image carrier such as a photoconductor, and the patch density is detected by an optical detection means (hereinafter also simply referred to as a sensor). A method of obtaining a toner adhesion amount of a gradation pattern from the detected value and obtaining a relational expression of the toner adhesion amount with respect to the development potential (slope: development γ, X intercept: development start voltage Vk) is widely used.
In these methods, the development potential is changed so that the target adhesion amount is obtained (specifically, LD power, charging bias, development bias is changed) based on the relationship between the calculated development potential and the toner adhesion amount, and the toner density control reference value. By changing this, a stable image density is always obtained.
As the optical sensor for detecting the toner adhesion amount of the gradation pattern, a type that detects only specular reflection light, a type that detects only diffuse reflection light, and a type that detects both are generally used. . These optical sensors are composed of light emitting elements such as LEDs and light receiving elements such as phototransistors.
The optical sensor irradiates the toner patch formed on the detection target surface with LED light, receives the reflected light (regular reflection light, diffuse reflection light) with a light receiving element such as a phototransistor, and the detection result is used as the toner adhesion amount. It has been converted.

However, in this optical sensor, the output of the light emitting element changes or the output of the light receiving element changes due to temperature change, deterioration with time, or the like. Furthermore, the output of the light receiving element also changes due to deterioration of the image carrier over time. For this reason, if the toner adhesion amount is uniquely determined from the output value of the light receiving element without correcting (calibrating) the output value of the light receiving element, there is a problem that the toner adhesion amount cannot be accurately detected.
Various techniques have been proposed in the past to solve such a problem that it is impossible to accurately detect the toner adhesion amount (see, for example, Patent Documents 1 to 3).
In Patent Document 1, a white reference plate is provided inside the optical sensor, and the calibration of the optical sensor is performed using this calibration plate, so that the toner adhesion amount can be accurately calculated even with changes over time of the optical sensor. Techniques for performing are disclosed.
Patent Document 2 includes a light receiving element that receives a regular reflection light and a light receiving element that receives diffuse reflection light by creating a gradation pattern composed of 10 to 16 toner patches having different toner adhesion amounts for each color. And a method for calculating the calibration of the optical sensor and the toner adhesion amount from the detection value of the optical sensor.
Therefore, since the optical sensor can be calibrated without providing a calibration plate inside the optical sensor, the toner adhesion amount can be accurately calculated without increasing the cost of the sensor.

Japanese Patent Application Laid-Open No. 2004-228561 has a means for obtaining the toner adhesion amount using an optical sensor including a light receiving element that receives specularly reflected light and a light receiving element that receives diffusely reflected light, and calibration of the optical sensor. A technique for changing the density of a toner patch necessary for the purpose based on past detection results is disclosed.
Therefore, it is possible to create a toner patch for calibrating the optical sensor and calculating the development γ without creating many toner patches. That is, since the number of toner patches can be reduced, this is a very effective method from the viewpoint of reducing toner consumption and downtime of the image forming apparatus.
Patent No. 3982188 JP 2004-354623 A JP 2006-139180 A

However, in the technique of Patent Document 1, having a calibration plate inside the optical sensor increases the cost of the optical sensor. Further, in the method of Patent Document 2, a toner patch of 10 to 16 patches is created for each image density adjustment, but this is not desirable from the viewpoint of reducing the toner consumption as much as possible.
In addition, since the number of gradation patterns is large, the total length of the gradation pattern formed on the intermediate transfer belt becomes long, and the time from when the optical sensor starts detection to when it ends is long. . That is, there is a problem that the downtime of the image forming apparatus used for adjusting the image density becomes long.
Furthermore, in the technique of Patent Document 3, the condition that the calibration of the optical sensor is originally required is that when the output characteristics of the light emitting element and the light receiving element used in the optical sensor change due to an increase in ambient temperature, the optical sensor When the detection surface of the belt becomes dirty due to toner scattering, etc., the surface condition of the detection target surface (transfer belt) has become rough, and the detection conditions have changed, such as when the specular reflection light output from the background of the belt has decreased. Is the case.

The above-described factors that require calibration of the optical sensor are all due to changes over time, and are not sudden and frequent. Therefore, the calibration of the optical sensor does not necessarily have to be performed every time the image quality adjustment is performed, and may be performed only when the calibration of the optical sensor is necessary. In this case, it is not necessary to create a toner patch for calibrating the optical sensor, and thus the number of toner patches to be created can be reduced.
Accordingly, an object of the present invention is to calibrate an optical sensor based on a detection value of a gradation pattern formed from a toner patch in consideration of the above-described situation, when calibration of the optical sensor is not necessary. An object of the present invention is to provide an image density control apparatus, an image density control method, and an image forming apparatus using the image density control method, which reduce the toner consumption and the image quality adjustment time by changing the number of gradation patterns to be created. .

In order to solve the above problems, the invention according to claim 1 is to develop an electrostatic latent image formed on the surface of the image carrier with a developer including toner carried on the developer carrier and a magnetic carrier. a developing device for a gradation pattern of different toner patches of urging Chakuryou formed on the detection target surface, created by the toner attached amount based on the diffuse reflection light output value obtained by the gradation pattern by the light sensing In an image forming apparatus for determining an image condition, a determination unit that determines whether or not sensitivity correction of the optical detection unit is necessary, and a case in which the sensitivity correction of the optical detection unit is determined by the determination unit A toner patch number changing means for forming a sensitivity correction gradation pattern comprising a predetermined number of toner patches in addition to the gradation pattern on the detection target surface, and the sensitivity correction detected by the optical detection means. The corrected diffuse reflection output value after correction is obtained by multiplying the corrected diffuse reflection output value obtained by removing the value based on the diffuse reflection output value from the background portion of the detection target surface from the diffuse reflection output value from the gradation pattern. Coefficient calculating means for calculating a sensitivity correction coefficient for correcting the toner to a predetermined value corresponding to the toner adhesion amount, and when the determination means determines that the sensitivity correction is not necessary, the toner patch number changing means The image forming apparatus determines the image forming condition using the sensitivity correction coefficient calculated last time without forming the sensitivity correction gradation pattern and calculating the sensitivity correction coefficient by the coefficient calculation means .

Further, in the invention according to claim 2, the determination means calculates an average value of reflected light output from the background portion of the detection target surface in the light detection means within a predetermined period, and the average value is within a predetermined range. sensitivity correction of the optical detection means is determined to be necessary when it is outside, wherein when average values are within the predetermined range, to claim 1, wherein the sensitivity correction is determined to be unnecessary of said optical detection means The image forming apparatus described above is characterized.

According to a third aspect of the present invention, the determination unit determines the necessity of correcting the sensitivity of the optical detection unit according to a temperature change from the previous LED current adjustment of the optical detection unit. The image forming apparatus according to claim 1 is characterized.
According to a fourth aspect of the present invention, the determination means determines the necessity of correcting the sensitivity of the optical detection means according to the number of printed sheets since the previous LED current adjustment of the optical detection means. The image forming apparatus according to claim 1 is characterized.
According to a fifth aspect of the present invention, when the determination unit determines that the sensitivity correction is not necessary and the sensitivity correction gradation pattern is not formed, the detection used for calculating the toner adhesion amount is performed. 5. The image forming apparatus according to claim 3 , wherein the specular reflection output value and the diffuse reflection output value from the background portion of the target surface use values at the time of previous image quality adjustment.
According to a sixth aspect of the present invention, when it is determined by the determining means that the sensitivity correction is not necessary and the sensitivity correction gradation pattern is not formed, the sensitivity used for calculating the toner adhesion amount is used. 5. The image forming apparatus according to claim 1, wherein the correction coefficient uses a value at the time of previous image quality adjustment.

According to a seventh aspect of the present invention, the developer carrier disposed opposite to the image carrier carries a two-component developer composed of toner and a magnetic carrier, and the two-component developer is supported on the image carrier. in the developing area formed between the body and the detection target and a step of developing the electrostatic latent image formed on said image bearing member surface with the toner, a gradation pattern of different toner patches of urging Chakuryou And forming an image forming condition based on a toner adhesion amount based on a diffuse reflection light output value obtained by light detection of the gradation pattern formed on a surface. A determination step for determining whether or not sensitivity correction is necessary, and a sensitivity composed of a predetermined number of toner patches in addition to the gradation pattern when the determination step determines that sensitivity correction of the optical detection means is necessary Tone for correction The number of toner patches on the surface to be detected is changed, and the diffusion from the diffuse reflection output value from the sensitivity correction gradation pattern detected by the optical detection means from the background portion of the surface to be detected Coefficient calculation for calculating a sensitivity correction coefficient for correcting the corrected diffuse reflection output value to a predetermined value corresponding to the toner adhesion amount by multiplying the corrected diffuse reflection output value from which the value based on the reflection output value is removed And when the determination step determines that it is not necessary to correct the sensitivity of the optical detection means, the sensitivity correction gradation pattern is formed by the toner patch number changing step and the coefficient calculation step is performed. The image forming method is characterized in that the imaging condition is determined using the sensitivity correction coefficient calculated last time without calculating the sensitivity correction coefficient .

According to an eighth aspect of the present invention, in the image forming method according to the seventh aspect, the determining step includes an average of the reflected light output from the background portion of the detection target surface in the light detection unit within a predetermined period. calculating a value, the average value is determined to be necessary sensitivity correction of the optical detection means when is outside the predetermined range, when the average value is within the predetermined range, the sensitivity of the optical detection means It is characterized by an image forming method that determines that correction is not necessary .

  According to the present invention, when the predetermined condition is satisfied, or when the average value of the regular reflection light output from the background portion of the intermediate transfer belt that is the detection target surface is calculated and is within the range of the preset value In this case, correction (calibration) of the optical sensor is not performed. For this reason, it is not necessary to create toner patches necessary for correction (calibration) of the optical sensor, so that it is possible to reduce the number of toner patches to be created at the time of image quality adjustment, and to reduce toner consumption.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a full-color printer which is an example of an image forming apparatus according to the present invention.
Four drum-shaped photosensitive drums 1Y, 1M, 1C, and 1Bk are arranged in parallel at equal intervals in the center of the main body of the full-color printer A shown in FIG. Y, M, C, and Bk indicate yellow, magenta, cyan, and black colors, respectively.
The following description will be given focusing on the photoreceptor 1Y for yellow image. The photosensitive drum 1Y is rotationally driven by a drive motor (not shown) in the clockwise direction in the drawing. Image forming means such as a charging roller 2, a developing device 4 having a developing roller 3, a cleaning device 7 and the like are sequentially arranged around the lower side of the photosensitive drum 1Y according to an electrophotographic process. The same applies to magenta, cyan, and black.
The surface of the photosensitive drum 1 is uniformly charged by a charging device 2 and then exposed by an optical system (not shown) to form an electrostatic latent image corresponding to image information. The developer in the developing device is conveyed to the developing nip region facing the photosensitive drum 1 by the developing roller 3 in the developing device 4, and toner is applied to the electrostatic latent image formed on the photosensitive drum 1 as an image carrier. Adhere and visualize.

The toner image formed on the photosensitive drum 1 is transferred onto an intermediate transfer belt 8 that is an image carrier disposed on the upper portion of the photosensitive drum 1. The toner images transferred onto the intermediate transfer belt 8 are transferred onto the intermediate transfer belt 8 in order with the movement of the intermediate transfer belt 8, and are overlaid.
The color-superposed toner images move to the secondary transfer device 12 and are transferred to transfer paper (not shown), and an image is formed on the transfer paper. The cleaning device 7 wipes away unnecessary toner remaining on the photosensitive drum 1 and stores unnecessary toner in a waste toner bottle. By repeating the above procedure, image formation is repeatedly performed.
The developing device 4 includes a developing roller 3 that is a developer carrying member, and the developing roller 3 is disposed so as to face the photosensitive drum 1. Further, the developing device 4 includes a biaxial conveying screw including a first screw 13 and a second screw 19. A toner concentration sensor 5 is provided at the lower portion of the developer chamber on the second screw 19 side.
As the toner concentration sensor 5, for example, a sensor that measures the toner permeability in the developing device is used. Here, in the toner density control, the output value: Vt of the toner density sensor is compared with the control reference value: Vtref of the toner density, and the toner replenishing amount is calculated from an arithmetic expression according to the difference, and the developing device is developed by the toner replenishing device. This is done by supplying toner inside.

In the image forming apparatus A in the present embodiment, apart from the image forming mode as described above, a process control operation is executed in order to optimize the image density of each color when the power is turned on or after a certain number of sheets have passed. The
In this process control operation, an image is formed on the intermediate transfer belt 8 by sequentially switching between a charging bias and a developing bias at appropriate timings as a density detection patch as a gradation pattern of each color.
As shown in FIG. 1, these gradation patterns are detected by an optical sensor 10 disposed outside the intermediate transfer belt 8 in the vicinity of the drive roller 15, and the output voltage is converted into an adhesion amount, thereby developing performance. Is calculated, and development bias value and toner density control target value are controlled based on the calculated values.
Here, the optical sensor 10 measures the amount of toner transferred from each color photosensitive drum 1 to the intermediate transfer belt 8. As a measuring method, a reference patch is created on the intermediate transfer belt 8 and irradiated with LED light. Then, the reflected light (regular reflected light or diffuse reflected light) from this pattern is detected. In the configuration of the optical sensor, a phototransistor, a photodiode, or the like is used as a light receiving element.

FIG. 2 is a flowchart showing the contents of the process control operation performed in this embodiment.
FIG. 3 is a flowchart for explaining the operation flow in the case of CMY for calibration control of the optical sensor in the calculation of the toner adhesion amount in the operation flow of FIG.
FIG. 4 is a schematic diagram showing a gradation pattern formed so as to correspond to the position where the optical sensor is provided.
FIG. 5 is a graph showing the relative luminous intensity and ambient temperature characteristics of the optical sensor.
FIG. 6 is a graph showing the detection output of the optical sensor.
FIG. 7 is a graph showing a calculation example of the sensitivity correction coefficient α.
FIG. 8 is a graph showing the regular reflection component decomposition.
FIG. 9 is a graph showing the nucleic acid reflection output after the background correction.
The contents of the process control operation performed in this embodiment will be described below with reference to FIGS. 1 and 4 together with the flowchart of FIG.

First, when the power is turned on, the bias of various motors and various devices is turned on when a predetermined number of sheets are printed, and preparations for executing process control are performed (device startup) (S1).
Next, the LED current of the optical sensor is adjusted as necessary (S2). The intermediate transfer belt background is irradiated with LED light, and the regular reflection light is detected. The LED current is adjusted so that the detected regular reflection light output is 4 V (this adjustment operation is hereinafter referred to as Vsg adjustment).
However, since it takes time to adjust Vsg, the LED current value at the time of the previous adjustment is used to irradiate the intermediate transfer belt background portion with LED light for a predetermined time, and its regular reflection light is detected, and the detected regular reflection light output is detected. (This operation is hereinafter referred to as Vsg_ave detection). If the average value is within the predetermined range, it is determined that there is no need to adjust the LED current, and Vsg adjustment is not executed.
Next, the output (Vt) of the toner density sensor 5 of the developing device 4 is acquired (S3). This is measured to know the current toner density, and is necessary for correcting the toner density (Vtref) described later.

Next, a gradation pattern is created (S4). This is necessary for detecting the development γ. In the present embodiment, specifically, the width 10 mm in the main scanning direction as shown in FIG. 4 so as to correspond to the position where the optical sensor 10 is provided, A gradation pattern is formed with a width of 14.4 mm in the sub-scanning direction and a pattern interval of 5.6 mm.
It is desirable that the number of gradation patterns for each color to be created be a number that fits in the pitch between the photosensitive drums. This is because if the total length of the gradation pattern of each color to be created is longer than the pitch between the photosensitive drums, it will overlap with other colors.
For this reason, writing of the next color gradation pattern must be started after delaying the writing and waiting for the creation of the gradation pattern of the other color. In such an operation, it takes a long time to create gradation patterns of all colors, and the time required for the adjustment operation increases.

In this embodiment, since the pitch between the photosensitive drums is 100 mm, the maximum number of gradation patterns that can be accommodated in the pitch between the photosensitive drums is (photosensitive drum pitch 100 mm) / (pattern sub-scanning). Direction width [14.4 mm] + pattern interval [5.6 mm]) = 5
Therefore, a toner patch is created with 5 or less patches for each color.
When writing the pattern, the exposure amount is full exposure (a value at which the photosensitive drum 1 is sufficiently discharged), and a gradation pattern is created by changing the development bias and the charging bias for each pattern (gradation pattern). A method for setting the developing bias and the charging bias at the time of creation will be described later).
Next, the gradation pattern is detected by the optical sensor 10 (S5). The optical sensor 10 detects the toner adhesion amount of each pattern in the gradation pattern created above and transferred to the intermediate transfer belt 8.
In the present embodiment, the Bk pattern detects only regular reflection light, and the C, M, and Y patterns detect both regular reflection light and diffuse reflection light. Further, only one optical sensor 10 for density detection is installed as shown in FIG. 4, and the gradation pattern of all colors is detected by this one sensor.

Next, the detection value of the optical sensor 10 is converted into the toner adhesion amount (S6). Here, a method for calculating the toner adhesion amount from the output value of the optical sensor 10 will be described. In the present embodiment, an optical sensor 10 including a light receiving element that receives regular reflection light and a light receiving element that receives diffuse reflection light is used to detect a toner patch having a high adhesion amount.
In the optical sensor 10, the output of the light emitting element changes or the output of the light receiving element changes due to a temperature change, deterioration with time, etc. shown in FIG. Furthermore, the output of the light receiving element also changes due to deterioration with time of the image carrier (intermediate transfer belt 8). For this reason, if the toner adhesion amount is uniquely determined from the output value of the light receiving element without performing any sensitivity correction (calibration) on the output value of the light receiving element, there is a problem that accurate toner adhesion amount cannot be detected. .
Therefore, the sensitivity correction (calibration) control of the optical sensor as described below is performed, and the adhesion amount of the toner patch is obtained from the output value of the light receiving element that receives diffuse reflected light (hereinafter, diffuse reflected light receiving element).

In the present embodiment, the amount of adhesion is calculated using the method described in Patent Document 3. Hereinafter, the optical sensor calibration control of the present embodiment will be described. In addition, the meaning of the symbol (abbreviation) in the following description is as follows.
Vsg: Background voltage Vsp of transfer belt Vsp: Output voltage Voffset of each pattern: Offset voltage (output voltage when LED_OFF)
_Reg. ... Specular reflection light output_dif. ... Diffuse reflected light output [n] ... Number of elements: n array variables (number of toner patches)
First, the case of Bk will be described. Data sampling in the case of Bk: Vsp, ΔVsg calculation. First, the difference from the offset voltage is calculated for all points [n] of the regular reflection light output. This is because the increase in the sensor output is represented only by the increase in the toner adhesion amount.

Specular light output increment:
ΔVsg_reg = Vsg_reg−Voffset_reg Expression (A)
ΔVsp_reg [n] = Vsp_reg [n] −Voffset_reg
... Formula (B)
Next, normal reflection light output is normalized: calculation of a normalization value Rn.
Normalized value Rn [n] = ΔVsp_reg [n] / ΔVsg_reg Expression (C)
Finally, the normalized value Rn is converted into an adhesion amount using the adhesion amount conversion table. An adhesion amount conversion table corresponding to the normalized value is created in advance, and the adhesion amount is obtained with reference to the adhesion amount conversion table for the normalized value. The above is the Bk adhesion amount conversion method.

Next, the case of C, M, and Y will be described with reference to the flowchart of FIG. Data sampling in the case of C, M, Y: Vsp, ΔVsg calculation (FIG. 6).
First, the difference from the offset voltage is calculated for all points [n] for both the regular reflection light output and the diffused light output (S11). This is because the increase in the sensor output is represented only by the increase in the toner adhesion amount.
Specular light output increment,
ΔVsp_reg. [N] = Vsp_reg. [N] -Voffset_reg
... Formula (1)
Diffuse light output increment,
ΔVsp_dif. [N] = Vsp_dif. [N] -Voffset_dif
... Formula (2)

Next, the sensitivity correction coefficient α is calculated (S12) (FIG. 7).
ΔVsp_reg. Determined in step (S11). [N], ΔVsp_dif. From [n], ΔVsp_reg. [N] / ΔVsp_dif. When [n] is calculated and the component decomposition of the regular reflected light output is performed, the coefficient α multiplied by the diffused light output (ΔVsp_dif [n]) is calculated.
α = min (ΔVsp_reg. [n] / Vsp_dif. [n] Expression (3)
Here, the ratio of α is obtained from the minimum value because it is known that the minimum value of the regular reflection component of the regular reflection light output is substantially zero and is a positive value.
The component decomposition of the regular reflection light is performed (S13) (FIG. 8).
The component decomposition of the regular reflection light output is performed by the following equation.
Diffuse light component of specular reflection output,
ΔVsp_reg. _Dif. [N] = ΔVsp_dif. [N] × α (4)
Specular component of specular reflection output,
ΔVsp_reg. _Reg. [N] = ΔVsp_reg. [N] -ΔVsp_reg. _Dif. [N] ... Formula (5)
In this way, if the diffuse light component is separated from the regular reflection light output, only a pure regular reflection light component can be extracted.

The regular reflection light output_regular reflection component is normalized (S14).
Next, the ratio of each pattern portion output to the belt background portion output is taken and converted into a normalized value from 0 to 1.
Normalized value,
β [n] = ΔVsp_reg. _Reg. / ΔVsg_reg. _Reg (Exposure rate of transfer belt background) Expression (6)
The background variation of the diffused light output is corrected (S15).
Next, a process of removing [diffused light output component from the background portion of the belt] from [diffused light output voltage] is performed.
Diffused light output after correction,
ΔVsp_dif. '= [Diffuse light output voltage] − [belt background output] × [normalized value of specular reflection component] = ΔVsp_dif. (N) -ΔVsp_dif. × β (n) (7)
The sensitivity correction of the diffused light output is performed (S16) (FIG. 9).
Plot the diffused light output after correcting the fluctuation of the background against the normalized value of regular reflected light (regular reflection component), and approximate the plot line to obtain the sensitivity of the diffused light output. Correction is performed so as to achieve a predetermined target sensitivity. As a method of approximating the plot line, polynomial approximation (secondary approximation) is used.

ｍ：データ数
ｘ［ｉ］：正反射光＿正反射成分の正規化値
ｙ［ｉ］：地肌部変動補正後拡散光出力
なお、計算に用いるｘの範囲は、本実施の形態では０．１≦ｘ≦１．００とする。 Next, a method for approximating the plotted points will be described. For the “normalized value of regular reflection light (regular reflection component)”, a plot line plotting the diffused light output after correction of background fluctuation is polynomial approximated (in this embodiment, quadratic approximation), A sensitivity correction coefficient η is calculated.
First, the plot line is approximated by a quadratic approximate expression (y = ξ1x2 + ξ2x + ξ3), and the coefficients ξ1, ξ2, and ξ3 are obtained by the least square method as described below.

m: Number of data x [i]: Regular reflection light_Normal reflection component normalized value y [i]: Diffusion light output after background portion fluctuation correction Note that the range of x used in the calculation is 0. 1 ≦ x ≦ 1.00.

ステップ（Ｓ１６）で求めた地肌部変動補正後の拡散光出力に対し、式（９）より求めた感度補正係数ηを乗じることで、付着量と拡散出力との関係が予め定められた関係となるように補正する。感度補正後の拡散光出力：△Ｖｓｐ＿ｄｉｆ”について
△Ｖｓｐ＿ｄｉｆ”＝［地肌部変動補正後拡散光出力］×［感度補正係数：η］＝△Ｖｓｐ＿ｄｉｆ（ｎ）”×η・・・式（１０）
以上が、ＬＥＤ光量低下などにより生じる光学センサの経時的な変動などに対する光学センサ出力値の補正（校正）制御（処理）である。上記のように補正することにより、温度変化、経時劣化などによる発光素子や受光素子の出力値変動に対して受光素子の出力値とトナー付着量との関係を一義的な関係に修正することができる。 The coefficients ξ1, ξ2, and ξ3 can be obtained by solving the simultaneous equations (1), (2), and (3) in the above equation (8). A sensitivity correction coefficient η is obtained so that a certain normalized value a calculated from the approximated plot line becomes a certain value b.

By multiplying the diffused light output after the background fluctuation correction obtained in step (S16) by the sensitivity correction coefficient η obtained from Equation (9), the relationship between the adhesion amount and the diffused output is a predetermined relationship. Correct so that Diffused light output after sensitivity correction: ΔVsp_dif ″ = [diffused light output after background fluctuation correction] × [sensitivity correction coefficient: η] = ΔVsp_dif (n) ″ × η (10)
The above is the correction (calibration) control (processing) of the optical sensor output value with respect to the temporal variation of the optical sensor caused by the LED light quantity reduction or the like. By correcting as described above, it is possible to correct the relationship between the output value of the light receiving element and the toner adhesion amount to a unique relationship with respect to fluctuations in the output value of the light emitting element or light receiving element due to temperature change, deterioration with time, etc. it can.

ΔVsp_dif ″ is converted into an adhesion amount using the adhesion amount conversion table (S17). After the correction (calibration) control of the output value of the optical sensor up to this step (S17), the corrected (calibrated) optical is performed. By referring to the adhesion amount conversion table based on the output value of the sensor, it is possible to convert the output value of the optical sensor into the toner adhesion amount, so that the optical sensor can detect a good toner adhesion amount over time. be able to.
However, as described above, the calibration of the optical sensor is performed when the output of the light emitting element or the light receiving element fluctuates due to a temperature change (see FIG. 5) or a change with time, and further receives light due to the deterioration with time of the detection target (intermediate transfer belt). Although it is necessary to perform this when the output of the element has changed, it is not always necessary to calibrate the optical sensor each time image quality adjustment is performed. Therefore, in this embodiment, when it is determined that calibration of the optical sensor is not necessary, the calibration value (sensitivity correction coefficient) at the previous adjustment is used, and the toner patch created for calibration is used. Try to reduce.
Returning to FIG. 2, next, development γ and development start voltage Vk are obtained (S7). The development γ and the development start voltage Vk are obtained from the relationship between the development potential at the time of toner patch image formation and the toner adhesion amount obtained in step (S6) described above.

FIG. 10 is a graph showing the relationship between the development potential and the toner adhesion amount. Specifically, as shown in FIG. 10, the horizontal axis represents the development potential, the vertical axis represents the toner adhesion amount, and a linear equation is obtained by the least square method. The slope of the linear equation is called development γ, and the X intercept is called development start voltage Vk.
Returning to FIG. 2 again, the developing bias necessary for obtaining the target toner adhesion amount is obtained (S8). The development potential (horizontal axis) is obtained from the target adhesion amount (vertical axis) based on the above linear equation.
The target adhesion amount is determined in advance as a value necessary for obtaining the top concentration (determined by the coloring degree of the toner pigment and the toner particle diameter, but is generally about 0.4 to 0.6 mg / cm ^2. ). The development bias value obtained here is defined as development bias Vb of the image area. The charging bias: Vc is determined in advance so that the carrier does not fly to the photoconductor (Vb = 400 to 750 V, Vc = Vb + 100 V to 200 V is generally used). Vb and Vc obtained in this way are set as biases at the time of image formation.

Finally, the toner density control reference value (Vtref) is corrected (S9). The toner density control reference value (Vtref) is corrected from the development γ and the toner density sensor output (Vt).
That is, Δγ = development γ detection value−development γ target value is obtained. Here, the development γ target value is predetermined for each apparatus. For example, 1.0 mg / cm ² / kV {if the development potential is 1000 V (1 kV), 1.0 mg / cm ² of toner is detected on the photosensitive drum 1. Means to adhere to.
Further, {development starting voltage = 0V and target toner adhesion amount of 0.5 mg / cm ² requires a developing potential of 500V. Since development potential = Vb−Vl, when Vl = 50V, Vb = 550V. V1 represents a post-exposure potential and depends on the photoconductor characteristics because it is the potential of the photoconductor drum 1 when fully exposed}.
When Δγ exceeds a predetermined value, Vb exceeds a settable range or an abnormal image occurs. Therefore, the toner density control reference value (Vtref) is corrected so that Δγ becomes the target range. However, no correction is performed when Vt at this time is significantly different from Vtref.

As an example of correction,
Correction condition 1: When Δγ ≧ 0.30 mg / cm ² / kV (high) and Vt−Vtref ≧ −0.2V, Vtref = Vt−0.2V. That is, the control reference value is set so as to lower the toner density from the current time.
Correction condition 2: When Δγ ≦ 0.30 mg / cm ² / kV (low) and Vt−Vtref ≦ 0.2V, Vtref = Vt + 0.2V. That is, the control reference value is set so as to increase the toner density from the current time. Other than the correction condition 1 and the correction condition 2, Vtref = previous value.
The above is the operation flow of process control.
In the calculation of the development γ, it is desirable that the data points used when obtaining the linear line by the least square method are evenly distributed within the effective range. This is because when the data points are close, the accuracy of the development γ is deteriorated due to an error factor.
Here, the error factor means that the output of the sensor has an error due to variations in the toner adhesion amount of the patch due to the periodic unevenness of the developing sleeve or scratches on the transfer belt, and the toner adhesion amount cannot be detected accurately. is there.
For this reason, if the data points are close (the development potential at the time of gradation pattern creation is close), the difference in the attached amount of the patch to be formed becomes small. There is a risk of doing. From the above, it is required that toner patches for calculating the development γ are created by being evenly distributed within the effective range.

Hereinafter, a bias setting method (calculation method) of the gradation pattern to be created, which is shown in step (S4) of the process control operation described above with reference to FIG. 2, will be described. Here, a description will be given by taking as an example the case of creating a gradation pattern of 5 patches for each color. However, the number of patches of each color to be created is not limited to this.
First, the development bias of each color obtained from the result of the previous process control is acquired. Then, the maximum development potential: PotMax is obtained from the development bias. The maximum development potential can be obtained by the following formula (11).
Maximum development potential: PotMax = (development bias: Vb) − (potential after solid portion exposure: Vl) [−V] (11)
Here, the solid portion post-exposure potential: Vl is the photosensitive drum potential after the exposure, and is a value depending on the characteristics of the photosensitive drum. In this embodiment, Vl = 50 [−V]. For example, if the development bias is 550 [-V] as a result of the previous process control, the development potential is PotMax = 550-50 = 500 [-V]. As described above, the maximum development potential of each color is obtained using Expression (11).

  Subsequently, the development bias of the gradation pattern is calculated from the maximum development potential of each color. Here, development biases are calculated using different methods for Bk, C, M, and Y. This is because the adhesion amount detection method differs between Bk and C, M, and Y. In this embodiment, Bk detects the toner adhesion amount using only regular reflection light, and C, M, and Y detect the toner adhesion amount using regular reflection light and diffuse reflection light. In the case of Bk toner, the irradiated light is absorbed by the toner surface, and thus there is a characteristic that the sensitivity of diffuse reflection light cannot be obtained. For this reason, in the Bk toner, the toner adhesion amount is detected using only regular reflection light. In the case where the amount of adhesion is detected using only regular reflection light, the sensitivity decreases as the toner density increases, and therefore the detection range of the amount of adhesion is narrower than C, M, and Y. For the above reasons, gradation pattern density is set using different methods for Bk, C, M, and Y.

<For Bk>
The development bias is calculated by substituting the maximum development potential obtained from the equation (11) into the following equation (12).
VPn (Bk) = PotMax (Bk) × 2n / 15 + (potential after solid portion exposure: Vl) [−V] (12)
Here, n of VPn (Bk) represents the nth of the gradation pattern.
<C, M, Y>
The magnitudes of the maximum development potentials of the respective colors obtained by the equation (11) are compared, and the order is determined. The maximum development potential of each color is set to PotMAX (1), PotMAX (2), and PotMAX (3) in descending order.
For example, if the maximum development potential is C, M, and Y in descending order, PotMAX (1) = PotMAX (C), PotMAX (2) = PotMAX (M), PotMAX (3) = PotMAX (Y). However, if the acquired maximum development potential is the same, the order is C, M, and Y.

Here, the previous development γ of each color may be compared to give an order. For example, when the development γ is C, M, and Y in descending order, PotMAX (1) = PotMAX (Y), PotMAX (2) = PotMAX (M), PotMAX (3) = PotMAX (C). .
Subsequently, the sequenced development potential is substituted into the following equation (13) to calculate the development bias of the gradation pattern.
VPn (m) = PotMAX (m) × {(m + 3 (n−1))} / 15+ (potential after solid portion exposure: Vl) [−V] (13)
Here, VPn (m) represents the development bias of the patch, n in VPn (m) represents the n-th gradation pattern of each color, and m represents the bias order (1, 2, 3). The development bias of the gradation pattern of each color can be expressed as follows.
VP1 (1) = PotMAX (1) × 1/15 + Vl
VP1 (2) = PotMAX (2) × 2/15 + Vl
VP1 (3) = PotMAX (3) × 3/15 + Vl
VP2 (1) = PotMAX (1) × 4/15 + Vl
VP2 (2) = PotMAX (2) × 5/15 + Vl
VP2 (3) = PotMAX (3) × 6/15 + Vl
VP3 (1) = PotMAX (1) × 7/15 + Vl
VP3 (2) = PotMAX (2) × 8/15 + Vl
VP3 (3) = PotMAX (3) × 9/15 + Vl
VP4 (1) = PotMAX (1) × 10/15 + Vl
VP4 (2) = PotMAX (2) × 11/15 + Vl
VP4 (3) = PotMAX (3) × 12/15 + Vl
VP5 (1) = PotMAX (1) × 13/15 + Vl
VP5 (2) = PotMAX (2) × 14/15 + Vl
VP5 (3) = PotMAX (3) × 15/15 + Vl
For example, VP2 (3) indicates the second patch having the lowest developing bias obtained from the previous process control result.
Next, the charging bias of the gradation pattern is set using the calculated development bias. The setting of the charging bias is calculated using Equation (14) common to Bk, C, M, and Y.
Charging bias: VPcn (color) [V] = VPn (color) × (1 + 0.01 × background potential coefficient) + background potential offset Equation (14)
However, as for the setting of the charging bias, the background potential coefficient and the background potential offset are set so that the background dirt does not occur.

FIG. 11 is a graph showing an outline of gradation pattern calculation. FIG. 11 shows an outline of gradation pattern calculation in the case of (PotMAX (1) = PotMAX (C))> (PotMAX (2) = PotMAX (M))> (PotMAX (3) = PotMAX (Y)). Is shown.
Here, the reason for ranking the colors by comparing the magnitude relationships based on the previous development bias of each color and setting the patch density of the gradation pattern based on the ranking will be described.
This is because the development γ is more stably calculated even when the developer characteristics change. In this method, based on the development bias of each color at the time of the previous process control, ranking is performed based on the magnitude relationship, and the bias value of the gradation pattern is set based on the result.
As shown in FIG. 11, compared to the other colors, when the development bias is low (development γ is high), it is on the high adhesion amount side, and when the development bias is high (development γ is low), the low adhesion amount is low. Create a toner patch on the side. Thus, by creating toner patches, it becomes possible to create more toner patches within the effective range when calculating development γ. The above is the gradation pattern bias calculation method in the present embodiment.
As described above, by setting the gradation pattern bias and calculating the toner adhesion amount, the development γ can be detected with high accuracy, and a stable image density can be obtained.

However, since the development γ detection method according to this embodiment described above simultaneously corrects (calibrates) the optical sensor, it is necessary to create a toner patch necessary for calibration.
Here, when the correction (calibration) of the optical sensor is necessary, when the output characteristics of the light emitting element and the light receiving element used in the optical sensor change due to an increase in the ambient temperature, the detection surface of the optical sensor is the toner. The surface of the detection target surface (intermediate transfer belt) becomes rough and the specular reflection light output from the background portion of the belt decreases.
The above-mentioned factors that require correction (calibration) of the optical sensor are all due to changes over time and cannot occur suddenly or frequently. Therefore, calibration of the optical sensor performs image quality adjustment. In this case, it is not always necessary to carry out the measurement every time, but only when the optical sensor needs to be calibrated.
Therefore, in this embodiment, it is determined whether correction (calibration) of the optical sensor is necessary based on the temperature change from the previous adjustment of the LED current of the optical sensor and the number of printed sheets. When it is determined that calibration of the optical sensor is not necessary, the previous value is used as the calibration value (sensitivity correction coefficient) of the optical sensor. Therefore, since it is not necessary to create a toner patch necessary for correction (calibration), a gradation pattern with a reduced number of toner patches is created, and development γ is calculated.
As described above, it is possible to reduce the amount of toner consumption and the time required for image quality adjustment by determining whether the correction (calibration) of the optical sensor is necessary and changing the number of toner patches to be created. Become.

FIG. 12 is a flowchart showing an operation flow for changing the number of gradation patterns. The operation for determining the necessity for correction (calibration) of the optical sensor and changing the number of toner patches will be described below with reference to the flowcharts of FIGS.
First, information such as temperature and the number of sheets to be passed is acquired (S21). The temperature change up to the present and the number of sheets passed are obtained from the previous adjustment of the LED current. For the temperature change, the temperature at the previous LED current adjustment is stored in a nonvolatile memory, and a difference value from the current temperature is obtained.
For the number of sheets to be passed, a counter is provided that counts up each time one sheet is printed since the previous LED current adjustment. Then, when the LED current is adjusted, the counter is cleared.
Next, it is determined whether or not the optical sensor 10 is corrected (calibrated) (S22). The temperature change amount and the number of sheets passed in step (S21) are compared with a determination threshold value, and it is determined whether correction (calibration) of the optical sensor 10 is necessary.
Here, the reason why the necessity of calibration of the optical sensor is determined using the temperature change amount and the number of sheets passed will be described. The case where the correction (calibration) of the optical sensor is necessary is a case where the output variation of the semiconductor light emitting element and the light receiving element used in the optical sensor 10 occurs due to an increase in ambient temperature as described above. Therefore, it is determined whether there is a need for correction (calibration) of the optical sensor based on the amount of temperature change since the previous adjustment of the LED current.

In addition, when the surface property of the intermediate transfer belt 8 that is the detection target surface is rough, the regular reflection output is reduced, so that correction (calibration) of the optical sensor 10 is required. Such a change with time is determined by the number of sheets. Therefore, it is determined whether there is a need for correction (calibration) of the optical sensor 10 based on the number of sheets that have passed since the previous adjustment of the LED current.
If it is determined in step (S22) that correction (calibration) of the optical sensor 10 is not necessary, Vsg_reg and Vsg_dif at the previous image quality adjustment are used (S23).
Next, if it is determined in step (S23) that the optical sensor needs to be corrected (calibrated), the background portion of the intermediate transfer belt 8 is actually irradiated with the LED, and the regular reflection light output and the diffuse reflection light output are output. The average value is obtained (S24). As the LED current value at that time, a value obtained as a result of the previous adjustment of the LED current is used (this operation is hereinafter referred to as Vsg_ave detection).
In the present embodiment, the measurement sampling interval is 4 msec, the measurement time is 600 msec, the specular reflection light output (Vsg_reg) and the diffuse reflection light output (Vsg_dif) of the background are detected, and the average value is calculated.
Next, as a result of the detection of Vsg_ave obtained in step (S24), it is confirmed whether or not Vsg_reg is a value within a predetermined range (S25). In the present embodiment, when 3.5V ≧ Vsg_reg ≧ 4.5V, it is determined that correction (calibration) of the optical sensor is not necessary (Vsg_ave upper / lower limit determination).
Next, in step (S25), if the result of Vsg_ave is within the upper and lower limit range, the values of Vsg_reg and Vsg_dif obtained in step (S24) are used for the subsequent calculations (S26).
If it is determined in step (S22) and step (S25) that correction (calibration) of the optical sensor 10 is not necessary, it is not necessary to create a toner patch necessary for correction (calibration). A gradation pattern in which the number of toner patches is reduced is created (S27).

The development bias is calculated by changing Expressions (12) and (13) in the gradation pattern bias calculation method described above to Expressions (16) and (17) below. Here, a description will be given assuming that the number of gradation patterns to be created is two patches for each color. However, although the number of patches to be created is not limited to two patches for each color, it is necessary to create a toner patch for at least two patches for each color in order to calculate development γ.
<Bk>
VPn (Bk) = PotMax (Bk) × 2n / 6 + (potential after solid portion exposure: Vl) [−V] (16)
<CMY>
VPn (m) = PotMAX (m) × {(m + 3 (n−1))} / 6+ (potential after solid portion exposure: Vl) [−V] (17)
The charging bias is calculated using Expression (14). A gradation pattern is created using the development bias and the charging bias obtained by the above calculation formula. By setting the gradation pattern bias as described above, the gradation pattern bias can be created evenly distributed.
By creating the gradation pattern evenly distributed, it is possible to prevent deterioration in development γ calculation accuracy due to error factors such as variations in the amount of toner adhesion due to periodic unevenness of the developing sleeve 3 and scratches on the intermediate transfer belt 8. .
Since it is not necessary to perform correction (calibration) of the optical sensor, the values at the time of the previous adjustment are used as they are for the sensitivity correction coefficients α and η obtained by the equations (3) and (9) in the toner adhesion amount calculation described above. (S28).

If it is determined in step (S25) that the result of Vsg_ave is outside the upper and lower limits, the LED current is adjusted (S29). The LED current is adjusted so that the specular reflection light output value of the background portion of the intermediate transfer belt 8 is 4 [V] (Vsg adjustment).
Further, the values of Vsg_reg and Vsg_dif after execution of Vsg adjustment are used for the subsequent calculations. However, since Vsg adjustment takes time, step (S29) is skipped according to the process control execution timing. Specifically, when process control is executed by an interruption during printing, the image quality adjustment time becomes long, so it is not performed.
A gradation pattern is created using the pattern bias calculated by the gradation pattern bias calculation method described above (S30). Next, sensitivity correction coefficients α and η are calculated using the optical sensor calibration control method described above (S31). Next, the toner adhesion amount is calculated from the detection value of the optical sensor 10 (S32). Finally, development γ is calculated from the relationship between the development potential at the time of toner patch image formation and the toner adhesion amount obtained in step (S32) (S33).
The above is the control for changing the number of toner patches in the present invention. When it is determined that calibration of the optical sensor 10 is not necessary, the number of toner patches is reduced, and Vsg_ave detection is not performed, so that it is possible to reduce the amount of toner consumption and the time required for the adjustment operation. .

Next, the pattern creation operation of the present invention will be described. When correction (calibration) of the optical sensor is required, a gradation pattern of 20 patches in total for each color with 5 patches and 4 colors is created. When correction (calibration) is not required, a total of 8 patterns with 2 patches for each color and 4 colors in total. The following description will be given on the assumption that a patch gradation pattern is created.
In order to show the effect of shortening the time when it is determined that correction (calibration) of the optical sensor 10 in this embodiment is not necessary, the following two operations are compared. That is, it is determined that this comparison requires correction (calibration) of the optical sensor, Vsg_ave detection is performed, a gradation pattern of five patches for each color is created, and no correction (calibration) of the optical sensor is required. This is the case where a gradation pattern of two patches for each color is created.
FIG. 13 is a diagram showing gradation patterns created when a gradation pattern of 5 patches for each color is created and when a gradation pattern of 2 patches for each color is created.
FIG. 14 is a table showing each parameter in the present embodiment.
When a gradation pattern of 5 patches for each color is created, Vsg_ave detection is performed using the Bk write end signal immediately before the process control as a reference, and the gradation pattern is created simultaneously for all colors using the end as a trigger.
Detection ends up to the final pattern of Y. Therefore, the time taken to detect the gradation pattern is Vsg_ave detection + (pitch between photosensitive drums × 4 colors) / linear velocity. When this is calculated using the parameters shown in FIG. 14, it is 3.93 (sec).

When a gradation pattern of two patches for each color is created, since Vsg_ave detection is not performed, a gradation pattern can be created with reference to a signal for completion of writing of each color immediately before process control.
However, if a gradation pattern is created from the write end signal for each color, all colors overlap. This is because in the present embodiment, detection is performed by the optical sensor 10 having the same color for all colors. For this reason, for the color on the upstream side, the start of the writing time must be delayed by the time for creating the gradation pattern on the downstream side.
From the above, when a gradation pattern of two patches for each color is created, the time required for detection of the gradation pattern is from the Bk write end signal to the final Y pattern,
{Toner patch sub-scanning length × total number of toner patches + interval length × (total number of toner patches−1)} / linear velocity. When calculated using the parameters shown in FIG. 14, it is 1.29 (sec).
Comparing the time taken for the gradation pattern detection time when a gradation pattern of 5 patches for each color is created and when the gradation pattern of 2 patches for each color is created, it is about 2 when the gradation pattern of each color is created. .5 seconds can be shortened.

As described above, when it is determined that calibration of the optical sensor is not necessary according to a predetermined condition from the previous LED current adjustment, it is not necessary to create a toner patch for performing correction (calibration). Therefore, the number of toner patches to be created can be reduced, and the amount of toner consumed when adjusting the image quality can be reduced. Further, the time required for correction (calibration) can be shortened by reducing the number of toner patches.
In addition, the necessity of calibration of the optical sensor is judged according to the average value of the reflected light output from the background of the detection target surface, and if it is judged that correction (calibration) of the optical sensor is not necessary, the correction is made. Since there is no need to create toner patches for performing (calibration), the number of toner patches to be created can be reduced, and the amount of toner consumed when adjusting image quality can be reduced. Further, the time required for correction (calibration) can be shortened by reducing the number of toner patches.
As described above, by using the image density control method that can reduce the number of toner patches to be created and reduce the amount of toner used when adjusting the image quality, the toner consumption and the time required for the image quality adjustment can be reduced. It is possible to provide an image forming apparatus capable of

1 is a schematic configuration diagram illustrating a full-color printer which is an example of an image forming apparatus according to the present invention. It is a flowchart which shows the content of the process control operation | movement performed in this Embodiment. 3 is a flowchart for explaining the operation flow in the case of CMY for calibration control of an optical sensor in the calculation of toner adhesion amount in the operation flow of FIG. It is the schematic which shows the gradation pattern formed so that it might correspond to the position in which the optical sensor was provided. It is a figure which shows the relative luminous intensity and ambient temperature characteristic of an optical sensor with a graph. It is a figure which shows the detection output of an optical sensor with a graph. It is a figure which shows the example of calculation of the sensitivity correction coefficient (alpha) by a graph. It is a figure which shows regular reflection component decomposition | disassembly with a graph. It is a figure which shows the nucleic acid reflection output after background part correction | amendment with a graph. It is a figure which shows the relationship between development potential and toner adhesion amount with a graph. It is a figure which shows the outline of a gradation pattern calculation with a graph. It is a flowchart which shows the operation | movement flow for changing the number of gradation patterns. It is a figure which shows the gradation pattern produced when the gradation pattern of each color 5 patch is produced, and when the gradation pattern of each color 2 patch is produced. It is a figure which shows each parameter in this Embodiment as a table | surface.

Explanation of symbols

  A image forming apparatus, 1 image carrier (photosensitive drum), 2 developer carrier (developing sleeve), 3 developing roller, 4 developing device, 8 detection target surface (intermediate transfer belt), 10 optical detection means (optical) Sensor), 19 second screw, S4 gradation pattern (toner patch) creation step (gradation pattern (toner patch) creation means), S6 toner adhesion amount calculation step (toner adhesion amount calculation means), S16 optical sensor output value calibration Step (optical sensor output value calibration means), S24 Average value calculation process of reflected light output from the background portion of the detection target surface (average value calculation means of reflected light output from the background portion of the detection target surface), S33 Development γ calculation (Toner patch number change) step (development γ calculation (toner patch number change means)

Claims (8)

Gradation pattern including the developing device, consisting of different toner patches of biasing Chakuryou be developed with a developer containing a toner and a magnetic carrier an electrostatic latent image carried on the developer carrying member which is formed on an image bearing member surface In an image forming apparatus for determining an image forming condition based on a toner adhesion amount based on a reflected light output value obtained by light detecting the gradation pattern.
Determination means for determining whether or not sensitivity correction of the optical detection means is necessary;
When the determination means determines that sensitivity correction of the optical detection means is necessary, a sensitivity correction gradation pattern including a predetermined number of toner patches is formed on the detection target surface in addition to the gradation pattern. Means for changing the number of toner patches;
A sensitivity correction coefficient for correcting the corrected diffuse reflection output value to a predetermined value corresponding to the toner adhesion amount is calculated from the diffuse reflection output value from the sensitivity correction gradation pattern detected by the optical detection means. Coefficient calculating means for calculating by multiplying the corrected diffuse reflection output value after removing the diffuse reflection output value from the background portion,
If it is determined by the determining means that the sensitivity correction is not necessary, the sensitivity correction coefficient is not calculated by the toner patch number changing unit and the coefficient calculating unit does not calculate the sensitivity correction coefficient. An image forming apparatus , wherein the image forming condition is determined using the calculated sensitivity correction coefficient . The determination means calculates an average value of reflected light output from the background portion of the detection target surface in the light detection means within a predetermined period, and the sensitivity of the optical detection means when the average value is outside a predetermined range. correction is deemed necessary, wherein when average values are within the predetermined range, the image forming apparatus according to claim 1, characterized in that it is determined that there is no need the sensitivity correction of the optical detection means. The determination means includes
Last in accordance with the temperature change from the time of the LED current adjustment, the image forming apparatus according to claim 1, wherein the determining the need for sensitivity correction of the optical detection means of the optical detection means. The determination means includes
Previous depending on the number of printed sheets from the time of the LED current adjustment, the image forming apparatus according to claim 1, wherein the determining the need for sensitivity correction of the optical detection means of the optical detection means. When it is determined by the determining means that the sensitivity correction is not necessary and the gradation pattern for sensitivity correction is not formed,
5. The image formation according to claim 3, wherein the specular reflection output value and diffuse reflection output value from the background portion of the detection target surface used when calculating the toner adhesion amount use values at the time of previous image quality adjustment. Equipment . When it is determined by the determining means that the sensitivity correction is not necessary and the gradation pattern for sensitivity correction is not formed,
5. The image forming apparatus according to claim 1, wherein the sensitivity correction coefficient used for calculating the toner adhesion amount uses a value at the time of previous image quality adjustment. A developer carrier disposed opposite to the image carrier carries a two-component developer composed of toner and a magnetic carrier, and the two-component developer is developed in the development area formed between the image carrier and the image carrier. Developing the electrostatic latent image formed on the surface of the image carrier with the toner;
The gradation pattern of different toner patches of urging Chakuryou formed on the detection target surface, and determining the image forming conditions by the toner attached amount based on the reflected light output value obtained by the gradation pattern by the light sensing In an image forming method comprising:
A determination step of determining whether sensitivity correction of the optical detection means is necessary;
When it is determined in the determination step that sensitivity correction of the optical detection unit is necessary, a gradation pattern for sensitivity correction including a predetermined number of toner patches is formed on the detection target surface in addition to the gradation pattern. A toner patch number changing step;
A sensitivity correction coefficient for correcting the corrected diffuse reflection output value to a predetermined value corresponding to the toner adhesion amount is calculated from the diffuse reflection output value from the sensitivity correction gradation pattern detected by the optical detection means. A coefficient calculating step of calculating by multiplying the corrected diffuse reflection output value after removing the diffuse reflection output value from the background portion,
If it is determined that the sensitivity correction of the optical detection means is not necessary in the determination step, the sensitivity correction coefficient is calculated by the formation of the sensitivity correction gradation pattern by the toner patch number changing step and the coefficient calculation step. The image forming method is characterized in that the image forming condition is determined using the sensitivity correction coefficient calculated last time without performing the step . The image forming method according to claim 7.
The determination step calculates an average value of reflected light output from the background portion of the detection target surface in the light detection unit within a predetermined period, and the sensitivity of the optical detection unit when the average value is out of a predetermined range. correction is deemed necessary, the average value when it is within the predetermined range, the image forming method characterized in that it is determined that the sensitivity correction is not required of the optical detection means.

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