JPH1090993A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To output good images by using two reference images so as to accurately control toner concentration. SOLUTION: A reference image forming part 25 forms a black solid patch on a photosensitive body 6 by a low light quantity and a texture patch by a high light quantity. A developing characteristic estimating part 22 approximates a developing potential from a middle concentration part to a high concentration part, which is a difference between a photosensitive surface potential measured by a surface potentiometer 14 and a developing bias added to a developing means, and a toner sticking amount measured by a toner sticking amount sensor 15 by a linear equation. A condition control part 23 controls an image forming condition based on the approximated relation between the developing potential and the toner sticking amount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image by an electrophotographic process such as a copying machine, a printer, a facsimile, etc., and more particularly to a method for stabilizing a toner adhesion amount of a formed image.

[0002]

2. Description of the Related Art In a multi-tone full-color copying machine, printer, or the like, it is desired to output an image with stable density with high accuracy. However, in the electrophotographic process used in these apparatuses, the density of an image fluctuates due to deterioration of the photoconductor, toner, and developer and characteristic fluctuation due to the environment. A method and an image forming apparatus for obtaining a stable toner density by suppressing this fluctuation are disclosed in, for example, Japanese Utility Model Publication No. 60-4188, Japanese Patent Application Laid-Open Nos. 4-126462, 6-266190, and 7-253694. No. in the official gazette.

In Japanese Utility Model Publication No. 60-4188, a reference image is formed by using a line-shaped or dot-shaped pattern piece instead of a solid black piece having a uniform density as a reference density piece for toner density control. Then, the change in the toner density is detected to control the image density.

Japanese Patent Application Laid-Open No. Hei 4-126462 discloses that a reference patch is formed on a photoreceptor by inputting an output image signal based on a plurality of predetermined different reference density data to exposure means, and the formed reference patch is formed. The toner adhesion amount on the photosensitive member is read by a toner adhesion amount sensor, and the relationship between the read toner adhesion amount and the output image signal of the reference density data is detected.
An image signal conversion coefficient for converting the input image signal into an output image signal to be input to the exposure means is corrected based on the detected relationship so that the relationship between the input image signal and the toner adhesion amount becomes a predetermined target value.

In the density control disclosed in Japanese Patent Application Laid-Open No. Hei 6-266190, low-, medium-, and high-density reference patches are formed on a photoconductor, and the formed reference patches adhere to toner on the photoconductor. The amount is read by the toner adhesion amount sensor, the relationship between the output image signal and the toner adhesion amount is estimated from the toner adhesion amount of the three reference patches, and the input image signal is converted into an output image signal to be input to the exposure means. The correction amount of the signal conversion coefficient is calculated.

FIG. 3 shows the relationship between an output image signal obtained by converting an input image signal into a signal to be input to an exposure unit by an image signal conversion coefficient in an electrophotographic process and a toner adhesion amount.
As shown in the fourth quadrant, the output image signal is converted into the exposure amount of the exposure means. This exposure amount is related to the photoconductor surface potential in a latent image created by using the charging unit and the exposure unit as shown in the third quadrant of FIG. In addition, FIG.
As shown in the quadrant, the toner adhesion amount is related to the developing potential which is the difference between the photosensitive member surface potential and the developing bias potential of the developing means. As a result, as shown in the first quadrant of FIG. 3, the toner adhesion amount is determined by the output image signal. As described above, the relationship between the output image signal and the toner adhesion amount shows a higher-order relationship as shown in FIG. 3, but the relationship between the development potential and the toner adhesion amount is simple as shown in the second quadrant of FIG. Become a relationship. Since the relationship between the output image signal and the exposure amount shown in the fourth quadrant of FIG. 3 and the relationship between the exposure amount and the photosensitive member surface potential shown in the third quadrant of FIG. 3 have small short-term fluctuations, the user uses the device. The process can be executed at times when it is not necessary to acquire characteristics. On the other hand, the relationship between the developing potential and the toner adhesion amount changes depending on the toner charging amount and the like. The toner is consumed by the developing means every time printing is performed, and a new toner is used.
Be replenished. Therefore, the charge amount of the toner has a large short-term fluctuation. Therefore, in order to know the relationship between the output image signal and the toner adhesion amount, the relationship between the development potential and the toner adhesion amount should be examined in a short term. JP-A-7-2536
The control method disclosed in Japanese Patent Publication No. 94 pays attention to this point, and the potential of the latent image formed on the photoconductor by the output image signal and the developing bias of the developing means shown in the second quadrant of FIG. Focusing on the fact that the relationship between the potential difference, which is the potential difference, and the toner adhesion amount after developing the latent image can be approximately linearly approximated in the low-density portion and the middle-high density portion as shown in FIG. A plurality of patch patterns having different toner adhesion amounts are created on the body, and a plurality of patch patterns are formed.
The potential of the toner and the amount of toner adhesion are measured, and the developing characteristics of the developing means are calculated from the relationship between the plurality of measured potentials and the amount of toner adhesion to determine various potentials during image formation.

[0007]

As disclosed in Japanese Utility Model Publication No. 60-4188, a line-shaped or dot-shaped pattern is used.
When a toner image is corrected by detecting a change in toner density by forming a reference image using small pieces of the toner, it has been difficult to accurately correct the toner density of images having different densities.

Since the relationship between the output image signal and the toner adhesion amount is non-linear as shown in FIG. 3, when forming a high gradation image, the output image signal and the toner adhesion amount at each gradation are formed. It is necessary to find the relationship accurately. For this reason, as shown in, for example, JP-A-4-126462 and JP-A-6-266190, a reference patch is formed from output image signals based on a plurality of different reference density data, and In order to accurately estimate the toner-adhered amount relationship, it is necessary to prepare not only three reference patches of low density, medium density, and high density but also many reference patches, and it is not easy to correct the density.

Further, as disclosed in JP-A-7-253694, a potential potential, which is a difference between the potential of a latent image formed on a photoreceptor and the developing bias potential of a developing means, and the latent image are developed. In the case where the relationship between the subsequent toner adhesion amounts is linearly approximated in the low-concentration part and the medium-high concentration part, at least 2
One reference patch needs to be created for each of the low-density part and the medium-high density part. Further, as shown in FIG. 5, the measurement sensitivity of the sensor for detecting the toner adhesion amount decreases in the high-density portion and does not become linear, so that a reference patch for compensating for this is also required. In order to obtain approximate characteristics, it was necessary to create at least four reference patches.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned disadvantages, and provides an image forming apparatus capable of outputting a high-quality image by accurately controlling the toner density using two reference images. The purpose is to do so.

[0011]

An image forming apparatus according to the present invention forms an electrostatic latent image on a photoreceptor in accordance with an input image signal, and develops the formed latent image on a transfer material by developing means. An image forming apparatus for transferring an image to an image forming apparatus includes a reference image forming unit, a surface potential sensor, a toner adhesion amount sensor, a developing characteristic estimating unit, and a condition controlling unit. In a region other than the body region, a reference image of a solid black solid patch is formed at a low light amount, a reference image of a texture patch is formed at a high light amount, and a surface potential sensor is used for the two reference images before development. The surface potential on the photoreceptor was measured, the toner adhesion amount sensor measured the toner adhesion amount after development of each of the above reference images or after transfer to a transfer material, and the developing characteristic estimating means was measured by a surface potential sensor. Photoconductor The relationship between the developing potential in the intermediate density portion and the high density portion of the developing potential, which is the difference between the surface potential and the developing bias added to the developing means, and the toner adhesion amount measured by the toner adhesion sensor is expressed by a linear expression. Approximately, the condition control means controls the image forming condition from the relationship between the developing potential and the toner adhesion amount approximated by the developing characteristic estimating means.

The texture patch formed by the reference image forming means is preferably a line patch.

The developing characteristic estimating means estimates the relationship between the developing potential and the toner adhesion amount sensor in the low density portion from the approximate relationship between the developing potential and the toner adhesion amount sensor in the intermediate density portion to the high density portion. It is desirable to do.

The developing characteristic estimating means approximates the relationship between the developing potential of the low-density portion and the toner adhesion amount by a linear expression, and calculates each coefficient of the linear expression from the relationship between the intermediate-density portion and the high-density portion. It may be represented by the approximated linear expression, the intercept, the amount of the adhered saturated toner in the low density part, and the developing potential at the saturation point.

The developing characteristic estimating means approximates the relationship between the developing potential of the low density portion and the toner adhesion amount by a cubic expression, and each coefficient of the cubic expression approximates the relationship from the intermediate density portion to the high density portion. Slope, intercept and saturation toner at low concentration
The relationship between the adhesion amount and the medium-to-high density portion may be expressed by the developing potential and toner adhesion amount at the switching point between the linear expression and the cubic expression.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a control section of an electrophotographic process for attaching toner to an electrostatic latent image formed on a photosensitive member and visualizing the electrostatic latent image has a developing characteristic estimating section and a condition controlling section. . The condition control unit includes an exposure operation value determination unit, a charging operation value determination unit, and a reference image forming unit. The reference image forming section creates a solid black solid patch with a low light amount and a texture patch with a high light amount in an area different from the area of the photoconductor where an image is formed by the input image signal. The toner adhesion amount of the texture patch created with this high light amount is detected by a toner adhesion amount sensor and corrected to the toner adhesion amount corresponding to a solid black solid patch, and the nonlinear output characteristics of the toner adhesion amount sensor are corrected. Thus, it is possible to solve the problem that the toner adhesion amount in the high concentration region cannot be detected, and to accurately detect the toner adhesion amount in the high concentration region.

The surface potential of the solid patch and the texture patch before development on the photoreceptor is measured with a surface voltmeter, and the difference between the measured surface potential of the solid patch and the texture patch and the development bias voltage is calculated. That is, the developing potential at the low density point and the high light quantity, that is, the developing potential at the high density point are sent to the developing characteristic estimating unit. On the other hand, the toner adhesion amount sensor detects the toner adhesion amount of the solid patch and the texture patch after development, and sends the toner adhesion amount at the low density point and the toner adhesion amount at the high density point to the developing characteristic estimating unit. The developing characteristic estimating unit approximates the relationship between the developing potential and the toner adhesion amount with the linear expression from the development potential and the toner adhesion amount at the sent low density point and high density point. The exposure operation value determination unit corrects the image signal conversion processing based on the relationship between the development potential and the toner adhesion amount approximated by the development characteristic estimation unit, and converts the input image signal into the output image signal by the corrected image signal conversion processing. The charging operation value determining unit also generates a charging control signal from the relationship between the developing potential and the toner adhesion amount approximated by the developing characteristic estimating unit, and controls the charge applied to the photoconductor. Thus, an image corresponding to the development characteristics is formed, and an image having a stable density is always output.

By creating this texture patch as a line patch, the stability of the density of the solid patch and the texture patch is further improved, and the development characteristics are obtained with high accuracy.

The developing characteristic estimating unit approximates the developing characteristic, which is the relationship between the developing potential and the toner adhesion amount in the middle and high density regions, with a linear expression, and develops the image in the low density region using the approximated linear expression. The characteristics are similar. When approximating the development characteristic in the low density portion, it can be approximated by a predetermined function or by a linear expression or a cubic expression. By approximating the development characteristics in the low-density area by the linear expression, the development properties in the low-density area can be approximated by simple processing. In addition, by approximating the developing characteristics in the low-density portion by a cubic expression, an approximate expression of the developing characteristics in the low-density portion can be accurately obtained.

[0020]

FIG. 1 is a block diagram of one embodiment of the present invention.
As shown in the figure, the image forming apparatus irradiates a document placed on a document table of a reading unit (not shown) with light from a light source, and reads the reflected light with a CCD 1. After the image signal read by the CCD 1 is converted into a digital signal by the A / D converter 2, predetermined image processing is performed by the document image processing unit 3 and sent to the exposure operation value determination unit 4 as an input image signal. The exposure operation value determination unit 4 performs an image signal conversion process on the sent input image signal, determines an output image signal corresponding to the input image signal, and comprises the determined output image signal with a semiconductor laser element or the like. To the exposure control unit 5. The exposure control unit 5 controls the driving of the semiconductor laser device based on the output image signal sent, exposes the photosensitive member 6 with laser light corresponding to the output image signal, and forms an electrostatic latent image on the surface of the photosensitive member 6. To form

Around the photoreceptor 6, a charger 7 for applying a charge to the photoreceptor 6 and a developing roller 8 are provided with toner on the electrostatic latent image formed on the photoreceptor 6 so as to be visible. A developing unit 9 for forming an image, a transfer unit 10 for transferring a toner image to a transfer sheet, a separator 11 for separating the transfer sheet from the photoreceptor 6, and a transfer for transferring the transfer sheet from the paper supply unit to the transfer unit 10 A fixing roller 13 for fixing the toner image on the transfer paper separated from the roller 12 and the photosensitive member 6 is provided, and an image is formed by an electrophotographic process. Further, as a sensor for detecting environmental information of the photoconductor 6 and the developing unit 9, a surface voltmeter 14 for detecting a potential of the photoconductor 6 and a toner image of a toner image on the surface of the photoconductor 6 formed by the developing unit 9 are provided. A toner adhesion amount sensor 15 for measuring the adhesion amount,
Toner concentration sensor 16, temperature sensor 17, humidity sensor 1
8 are provided. The toner adhesion amount sensor 15 may be provided not only on the photosensitive member 6 but also on the transfer path 19 of the transfer paper.

As shown in the block diagram of FIG. 2, the density control unit of the electrophotographic process for attaching toner to the electrostatic latent image formed on the photoreceptor 6 and visualizing the electrostatic latent image includes a difference calculation unit 21 and a development characteristic estimation. And a condition control unit 23. The difference calculator 21 calculates a development potential P, which is a difference between the surface potential of the photosensitive member 6 measured by the surface voltmeter 14 and the development bias voltage of the development roller 8. The developing characteristic estimating unit 22 inputs the developing potential P calculated by the difference calculating unit 21 and the toner adhering amount TD of the reference image measured by the toner adhering amount sensor, and approximates the relationship between the developing potential P and the toner adhering amount TD. I do. The condition control unit 23 includes an exposure operation value determination unit 4, a charging operation value determination unit 24, and a reference image forming unit 25. The exposure operation value determination unit 4 corrects the image signal conversion process from the relationship between the development potential P and the toner adhesion amount TD approximated by the development characteristic estimation unit 22, and converts the input image signal into an output image signal by the corrected image signal conversion process. Convert. The charging operation value determining unit 24 generates a charging control signal from the relationship between the development potential P and the toner adhesion amount TD approximated by the developing characteristic estimating unit 22 and sends the signal to the charging control unit 26. The charging control unit 26 controls the charge applied by the charger 7 to the photoconductor 6 based on the transmitted charging control signal. The reference image forming unit 25 forms a reference patch on the surface of the photoconductor 6 using two preset reference density image data when performing image density control.

In describing the operation of the image forming apparatus configured as described above, various characteristics related to image density fluctuation of an output image when an image is formed by an electrophotographic process will be described.

In an image forming apparatus utilizing an electrophotographic process, as shown in the first quadrant of FIG. 3, there is a fixed relationship between the output image signal and the toner adhesion amount on the photoconductor 6,
If this relationship fluctuates, it is a major factor that the image density of the output image fluctuates. Conversely, if this relationship can be accurately detected, it can be estimated that the image density will fluctuate, and the image forming conditions such as the charge amount and the exposure amount of the photoconductor 6 are changed to the output image signal and the toner adhesion amount. By controlling in such a direction as to compensate for the change in the relationship, the image density change of the output image can be reduced.

This output image signal is directly related to the amount of exposure as shown in the fourth quadrant of FIG. That is, the exposure control unit 5 modulates the driving voltage of the semiconductor laser element, modulates the driving pulse width, or modulates both the driving voltage and the driving pulse width in response to the output image signal, and The laser light for exposing the surface is controlled. The relationship between the output image signal and the exposure amount fluctuates due to temperature characteristics, dirt on the surface of the photoconductor 6, and the like, but these fluctuations are small and do not fluctuate in a short time.

The exposure amount has a fixed relationship with the photoconductor surface potential as shown in the third quadrant of FIG. That is, as the exposure amount increases, the absolute value of the photoconductor surface potential decreases. This relationship changes due to sensitivity fluctuations caused by the surface of the photoreceptor 6 being scraped and the film thickness being reduced, sensitivity fluctuations of the photoreceptor 6 due to the temperature, temporary fluctuations in the sensitivity due to continuous image formation, and the like. However, fluctuations due to thickness reduction and temperature do not occur in a short period of time. Further, temporary sensitivity fluctuation due to continuous image formation mainly occurs in a high-exposure portion as shown by a dotted line in FIG. In the negative-positive development, the high exposure area corresponds to the high density area. Photoconductor 6
FIG. 5 shows the results of measurement of the toner adhesion amount of the toner image formed on the recording medium and the brightness when the toner image was transferred to a transfer sheet and fixed. As shown in FIG. 5, human vision has low sensitivity in the high-density portion, and cannot be detected even if the toner adhesion amount slightly fluctuates. Therefore, the short-term sensitivity fluctuation that temporarily occurs in the high-density portion due to continuous image formation is not so important in terms of stabilizing the image density. In addition, the relationship between the output image signal and the exposure amount and the long-term variation in the exposure amount and the photoconductor surface potential can be easily detected at a time when there is sufficient time such as when the user is not using the device. can do.

The development potential, which is the difference between the photoconductor surface potential and the development bias potential, and the toner adhesion amount are also shown in FIG.
There is a certain relationship as shown in the second quadrant. The relationship between the development potential and the toner adhesion amount is characterized in that it has linearity from a medium density portion to a high density portion where the toner adhesion amount is large. The inclination of this characteristic changes as shown by the dotted line in FIG. 6 largely due to the change in the charging characteristic of the toner. The change in the charge amount of the toner is greatly affected by humidity and a short-term variation in characteristics such as uneven charging occurs when the toner in the developing unit 9 is consumed and the newly replenished toner is charged. The short-term fluctuation of the output image density is mainly due to the fluctuation of the developing characteristic indicating the relationship between the developing potential and the toner adhesion amount. Therefore, it is important to detect the development characteristic indicating the relationship between the development potential and the toner adhesion amount in order to know the relationship between the output image signal and the toner adhesion amount.

The operation of controlling the image forming conditions by detecting the developing characteristics indicating the relationship between the developing potential and the toner adhesion amount in the image forming apparatus configured as described above will be described.

In order to know the characteristics in the high-density portion from the middle density to the development characteristics showing the relationship between the development potential and the toner adhesion amount, a development characteristic diagram showing the relationship between the development potential and the toner adhesion amount is shown in FIG. Thus, low concentration A and high concentration B
The following two patches may be created, and a linear first-order approximation may be made from the development potential and the toner adhesion amount. However, as shown in the characteristic diagram of the toner adhesion amount and the sensor output in FIG. 8, the output characteristic of the toner adhesion amount sensor 15 with respect to the toner adhesion amount is non-linear and the output characteristic of the toner adhesion amount sensor 15 is high. Since the output of the toner adhesion amount sensor 15 is attenuated in the density portion, the toner adhesion amount in the high concentration portion cannot be measured. That is, when the development characteristic diagram showing the relationship between the development potential and the toner adhesion amount in FIG. 7 is rewritten in consideration of the output characteristic of the toner adhesion amount sensor 15, a solid line in FIG. 9 is obtained. As shown in FIG. 9, the toner characteristic of the high density B reference patch
The amount of adhesion cannot be measured. Therefore, if the toner adhesion amount sensor 15 attempts to obtain the developing characteristics using the point C having linear sensitivity instead of the point B, the interval between the points A and C is narrow, and the developing characteristics can be obtained with high accuracy. Will be gone.

Therefore, as shown in FIG. 10, when the black solid patch 31a is formed with the same light quantity as the solid black patch 31a, the blackness of the solid patch 31a is reduced.
Texture patch 3 consisting of 50% halftone patches
The output of the toner adhesion amount sensor 15 for the solid patch 31a and the toner for the texture patch 31b when the exposure amounts of the two reference density image data 1b are changed.
The output of the adhesion amount sensor 15 is shown in FIG. 11 on the basis of the toner adhesion amount by the solid patch 31a. As shown in FIG. 11, the texture patch 31b is a solid patch 31a.
And the texture is different, the amount of toner attached when created with the same amount of light is reduced.
Even if the toner adhesion amount 1a is B, the texture patch 31b is in an area where the toner adhesion amount sensor 15 has linear sensitivity. Therefore, using the solid patch 31a, the toner adhesion amount when the low density A, that is, the exposure amount is small, is detected, and the high density B, that is, the toner adhesion amount when the exposure amount is large, is detected by the texture patch 31b. By correcting the toner adhesion amount detected by the toner adhesion amount sensor 15 in accordance with the blackness of the texture patch 31b, the toner adhesion amount at point B shown in FIG. 7 can be obtained.

By using the development potential Pa and toner adhesion Oa of the solid patch 31a at the point A and the development potential Pb and toner adhesion Ob of the texture patch 31b at the point B, as shown in FIG. The experimental results confirmed that the slope α and the intercept β of the linear linear expression of the development characteristic showing the relationship between the development potential P and the toner adhesion amount TD at In the following equation, the constants d, e, f, g, and h are obtained in advance by experiments.

TD = α · P + β α = (ji −) / (d · Pb−Pa) β = i−α · Pai = − (Oa−e) j = − (Ob−g) / h

Therefore, the reference image forming unit 25 creates a solid black patch 31a of low solid quantity shown in FIG. 10 in an area different from the area of the photoreceptor 6 where an image is formed by an input image signal, and The patch 31b is created with a high light quantity. Then, the surface potential of the solid patch 31a and the texture patch 31b before development on the photoconductor 6 is measured by the surface voltmeter 14 and sent to the difference calculation unit 21. Difference calculator 21
Is sent solid patch 31a and texture patch 3
The difference between the surface potential 1b and the developing bias voltage of the developing roller 8 is calculated, and the developing potential Pa at the point A and the developing potential Pb at the point B are sent to the developing characteristic estimating unit 22. On the other hand, the toner adhesion amount sensor 15 detects the toner adhesion amount of the developed solid patch 31a and the texture patch 31b, and the toner adhesion amount Oa at the point A and the toner adhesion amount at the point B via the adhesion amount correction unit 27. The attached amount Ob is sent to the developing characteristic estimating unit 22. The developing characteristic estimating unit 22 sends the developing potentials Pa and Pb and the toner adhesion amounts Oa and Ob.
Accordingly, the relationship between the development potential P and the toner adhesion amount TD is approximated by the above TD = α · P + β. The exposure operation value determination unit 4 corrects the image signal conversion processing from the relationship between the development potential P and the toner adhesion amount TD approximated by the development characteristic estimation unit 22,
The input image signal is converted into the output image signal by the corrected image signal conversion processing. The charging operation value determining unit 24 also generates a charging control signal from the relationship between the developing potential P and the toner adhesion amount TD approximated by the developing characteristic estimating unit 22, and generates a charging control signal.
The charging control section 26 controls the charge provided by the charger 7 to the photoconductor 6. Since an image corresponding to the development characteristics is output in this manner, an image having a stable density can be always output. In addition, the relationship between the development potential and the toner adhesion amount can be obtained with only two patches 31a and 31b using different light amounts for the development characteristics in the middle and high density regions and using different textures.

In the above embodiment, the texture patch 31 is used.
Although the case where b is formed by halftone patches has been described, by creating the texture patch 31b with line patches, the solid patch 31a and the texture patch 31b can be formed.
, And the developing characteristics can be obtained with high accuracy.

In the above-described embodiment, the case where the developing characteristic estimating unit 22 approximates the developing characteristic TD = α · P + β, which is the relationship between the developing potential P and the toner adhesion amount TD in the medium / high density region, has been described. The developing characteristics in the low density portion may be approximated together with the developing characteristics in the region.

That is, the relationship between the development potential P and the toner adhesion amount TD in the low-density portion fluctuates in correlation with the development characteristics of the middle and high-density portions as shown by the solid line and the dotted line in FIG. Therefore, when the relationship between the developing potential P and the toner adhesion amount TD in the middle and high density portions is approximated to the above TD = α · P + β, the development characteristics in the low density portion are TD = F (P, α,
β), the toner adhesion amount TD can be uniquely obtained from the development potential P, the gradient α of the development characteristic of the high density portion, and the intercept β. Then, the function F can be obtained in advance by an experiment, and the developing characteristic estimating unit 22 can obtain the developing characteristic of the low density portion by using the function F.

Although the above embodiment has been described with reference to the case where the developing characteristic of the low density portion is obtained by the function F determined by experiment, the developing characteristic of the low density portion can be approximated by a linear expression. For example, when the development characteristic of the high-density part of the development characteristic shown by the dotted line in FIG. 13 is approximated to TD = α · P + β, the gradient a of the linear expression approximating the development characteristic of the low-density part is It changes according to the characteristic gradient α, and can be expressed by a = k · α. Further, assuming that the toner adhesion amount at the point where the toner adhesion amount is saturated in the low density portion is TDd and the development potential is Pd, the development potential P in the low density portion and the toner adhesion amount TD
The linear equation approximating the relationship is: TD = a · (P−Pd) +
It can be expressed as TDd. If k, TDd, and Pd are determined in advance by an experiment, the developing characteristic estimating unit 22 can calculate the characteristic of the high-density part together with the approximate expression of the developing characteristic of the high-density part without creating a special patch to obtain the characteristic of the low-density part. An approximate expression of the development characteristics of the low density portion can be obtained. By approximating the development characteristics of the low-density portion by a linear expression in this way, the development characteristics of the low-density portion can be obtained by simple processing.

In the above embodiment, the case where the developing characteristics of the low-density portion are approximated by a linear expression is described. Characteristics can be obtained with higher accuracy. For example, when the developing characteristic of the low density part is approximated by a cubic equation, as shown in FIG. 14, when the developing characteristic of the high density part is approximated by TD = α · P + β, the toner adhesion amount in the low density part Saturation value T
In Dd, the first derivative has multiple solutions, that is, the maximum and minimum of the cubic equation coincide, and the cubic equation comes into contact with the linear equation approximating the high-density portion in terms of the development potential Pe and the toner adhesion amount TDe3.
The developing potential P and toner adhesion amount T in the low density portion are expressed by the following equation.
When the relationship of D is approximated, the approximated cubic expression can be expressed by the following expression.

[0039] ^{TD = a · P 3 + b} · P 2 + c · P + d a = A b = -3A · Pe 2 -2B · Pe + C c = 3A · Pe 3 + B · Pe 2 -C · Pe + D Pe = (TDe-β ^{) / α A = α 3 /} {27 · (TDd-TDe) 2} B = -α 2/3 · (TDd-TDe) C = α D = TDe

If TDe, TDe, and Pe are determined in advance by experiments, the developing characteristic estimating section 22 can accurately obtain the approximate expression for the developing characteristic of the high density portion and the approximate expression of the developing characteristic for the low density portion. it can. Therefore, an image having a stable density can be always formed.

[0041]

As described above, according to the present invention, a solid black solid patch is created with a low light intensity, a texture patch is created with a high light intensity, and the toner adhesion amount of the texture patch created with a high light intensity is measured. Since the toner adhesion amount is detected by the adhesion amount sensor and corrected to the toner adhesion amount corresponding to the solid black solid patch, the toner adhesion amount in the high density region cannot be detected due to the nonlinear output characteristic of the toner adhesion amount sensor. Thus, the toner adhesion amount in the high concentration region can be accurately detected.

Further, the surface potential of the solid patch and the texture patch before development on the photoreceptor is measured, and the difference between the measured surface potential of the solid patch and the texture patch and the development bias voltage is calculated to obtain a low light quantity, that is, a low density. The relationship between the developing potential at the point and the high light quantity, that is, the developing potential at the high density point and the toner adhesion amount at the low density point and the high density point, is approximated by a linear expression to approximate the relationship between the developing potential and the toner adhesion amount at the medium and high density regions. A short-term change in the developing characteristics is detected from the relationship between the developed potential and the toner adhesion amount, and the image forming conditions are controlled, so that an image corresponding to the developing characteristics can be formed, and an image with a stable density is always obtained. Can be output.

Further, by forming the texture patches using line patches, the stability of the density of the solid patches and the texture patches can be further improved, and the development characteristics can be obtained with high accuracy.

In addition, the developing characteristic, which is the relationship between the developing potential and the toner adhesion amount in the middle and high density regions, is approximated by a linear expression, and the developing characteristic in the low density portion is determined in advance by using the approximated linear expression. By approximating by a function or by a linear expression or a cubic expression, it is possible to detect short-term fluctuations in the development characteristics in a low density portion, and to form a stable image.

Further, by approximating the developing characteristics in the low density portion by a linear expression, the developing characteristics in the low density portion can be approximated by simple processing.

Further, by approximating the developing characteristic in the low density portion by a cubic expression, an approximate expression of the developing characteristic in the low density portion can be obtained with high accuracy, and a high quality image can be formed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an outline of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a density control unit according to the embodiment.

FIG. 3 is a characteristic diagram showing a relationship among an output image signal, an exposure amount, a photoconductor surface potential, a developing potential, and a toner adhesion amount.

FIG. 4 is a characteristic diagram showing a variation in sensitivity between an exposure amount and a photoconductor surface potential.

FIG. 5 is a characteristic diagram showing a relationship between a toner adhesion amount and brightness.

FIG. 6 is a graph showing a change characteristic of a development potential and a toner adhesion amount.

FIG. 7 is an explanatory diagram showing the principle when the relationship between the developing potential of the middle and high density portions and the toner adhesion amount is linearly approximated.

FIG. 8 is an output characteristic diagram of a toner adhesion amount sensor.

FIG. 9 is a change characteristic diagram showing a relationship between a developing potential and a toner adhesion amount detected by a toner adhesion amount sensor.

FIG. 10 is a configuration diagram of a solid patch and a texture patch.

FIG. 11 is an output characteristic diagram of a toner adhesion amount sensor for a solid patch and a texture patch when an exposure amount is changed.

FIG. 12 is an explanatory diagram when a relationship between a toner adhesion amount and a developing potential in a low density region is approximated by a function.

FIG. 13 is an explanatory diagram of a first-order approximation of the relationship between the toner adhesion amount and the development potential in a low-density region.

FIG. 14 is an explanatory diagram when the relationship between the toner adhesion amount and the developing potential in the low density region is approximated by third order.

FIG. 15 is an explanatory diagram showing a relationship between a toner adhesion amount and a developing potential in a conventional example.

[Explanation of symbols]

 Reference Signs List 4 Exposure operation value determination unit 5 Exposure control unit 6 Photoconductor 7 Charger 9 Developing unit 14 Surface voltmeter 15 Toner adhesion amount sensor 22 Development characteristic estimating unit 23 Condition control unit 24 Charging operation value determination unit 25 Reference image forming unit 31a Solid patch 31b Texture patch

Claims (5)

[Claims] An image forming apparatus that forms an electrostatic latent image on a photosensitive member in accordance with an input image signal, develops the formed latent image by a developing unit, and transfers the latent image to a transfer material; A surface potential sensor, a toner adhesion amount sensor, a developing characteristic estimating unit, and a condition controlling unit, and the reference image forming unit is provided with a low light amount in an area different from an area of the photoreceptor for forming an image based on an input image signal. A reference image of a solid black solid patch is formed, a reference image of a texture patch is formed with high light intensity, and a surface potential sensor measures the surface potential of the two reference images on the photoreceptor before development. The adhesion amount sensor measures the toner adhesion amount after the development of each of the reference images or after transfer to the transfer material. The developing characteristic estimating means includes a photoconductor surface potential measured by a surface potential sensor and a developing bias applied to the developing means. The relationship between the developing potential in the intermediate density portion and the high density portion of the developing potential, which is the difference between the developing potential, and the toner adhesion amount measured by the toner adhesion amount sensor is approximated by a linear expression, and the condition control means is a development characteristic estimating means. An image forming apparatus, wherein an image forming condition is controlled from an approximate relationship between a developing potential and a toner adhesion amount. 2. The image forming apparatus according to claim 1, wherein the texture patch formed by the reference image forming means is a line patch. 3. The developing characteristic estimating means estimates the relationship between the developing potential and the toner adhesion amount sensor in the low density portion from the approximate relationship between the developing potential and the toner adhesion amount sensor in the intermediate density portion to the high density portion. Claim 2
The image forming apparatus as described in the above. 4. The developing characteristic estimating means approximates the relationship between the developing potential of the low-density portion and the toner adhesion amount with a linear expression, and calculates each coefficient of the linear expression from the relationship between the intermediate-density portion and the high-density portion. 4. The image forming apparatus according to claim 3, wherein the slope is expressed by an approximated linear expression, an intercept, an attached amount of a saturated toner in a low density portion, and a developing potential at the saturation point. 5. The developing characteristic estimating means approximates the relationship between the developing potential of the low density portion and the toner adhesion amount by a cubic expression, and each coefficient of the cubic expression represents the relationship between the intermediate density portion and the high density portion. The slope of the approximated linear equation, the intercept, and the saturated toner in the low concentration area.
4. The image forming apparatus according to claim 3, wherein the relationship between the adhesion amount and the medium-high density portion is expressed by a developing potential and a toner adhesion amount at a switching point between a linear expression and a cubic expression.