JPH07230213A - Method for controlling reproduction of extra highlight for image forming device - Google Patents

Abstract

PURPOSE:To surely and easily obtain the stable reproducibility of extra highlight even when toner concentration in a developing device is changed in order to control the concentration at a middle/high concentration part to be constant. CONSTITUTION:When a power source is judged to come into on-state from off-state at a step Sl after it is turned on, humidity in an image forming part is measured by a humidity sensor at a step S2. Then, it is decided by an arithmetic unit whether the measured humidity is <=40%, between 40% and 70% or >=70% at a step S3. At a step S4, a chopping wave bias is set to be negative when the humidity is <=40%, set to be zero when it is between 40%, and 10% and set to be positive when it is >=70%. Then, the turning-on time of a laser is controlled based on the set chopping wave bias and the density of an image is adjusted. Thus, the density of the image at the extra highlight part is adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pole of an image forming apparatus for forming an image by developing a latent image formed by scanning a uniformly charged photosensitive member with a light beam of multi-gradation digital image data. More particularly, the present invention relates to a highlight reproduction control method, in which image density control means optically detects the reference patch density developed on the photoconductor and supplies toner based on the detected reference patch density so that the image density becomes constant. The present invention relates to an extreme highlight reproduction control method of an image forming apparatus for controlling the.

[0002]

2. Description of the Related Art In recent years, a digital image forming apparatus for irradiating a photosensitive body with a light beam modulated based on multi-tone digital image data to form a latent image has been actively announced. In this type of image forming apparatus, smooth reproducibility of the intermediate density portion is possible, but not only the background portion of the original is skipped to clearly reproduce the high density portion,
In order to reproduce an original having gradation like a photograph, it is necessary to stabilize the density of the intermediate density portion and below.

Generally, the sensitivity of the human eye is more sensitive to the middle density portion or less (density of about 1.2 or less) than that of the high density, and the lower the density is, the more noticeable it is. Is required to be higher than the stability in the high density portion, and especially in a color image forming apparatus, the density stability in the intermediate density portion and below is important. Among them, the stable reproducibility of the extremely highlighted portion with an image area ratio of about 15% or less, which is hardly considered in the conventional analog image forming apparatus, is so important that the image quality is improved in the digital image forming apparatus. It has become.

As a method of forming an image with multi-tone digital image data, the input multi-tone digital image data is converted into an analog signal and compared with a reference pattern of a predetermined cycle such as a triangular wave to perform pulse width modulation. A method is known which is performed based on the binarized signal generated.

In this method, since the output pulse width is determined by the magnitude relationship between the analog signal and the reference pattern, the relative magnitude relationship between the analog signal and the reference pattern has a great influence on the gradation of the reproduced image. become. In particular, the relationship between the black level and white level of the analog signal and the upper and lower peak levels of the reference pattern affects the gradation of the extremely highlighted part and the high density part, or the resolution of the overall reproduction gradation, which is important. ing.

Therefore, as disclosed in Japanese Patent Laid-Open No. 62-181575, the pulse width is detected and the pulse width between the black level and the white level is manually adjusted by the full scale range of the analog signal and the bias of the reference pattern. To adjust the bias of the reference pattern by detecting the pulse width as disclosed in Japanese Patent Laid-Open No. 4-336868, and as disclosed in Japanese Patent Laid-Open No. 63-177153. A light meter which detects the light quantity and manually adjusts the light quantity of a black level and a white level by the bias and gain of a reference pattern, or JP-A-62-09
As disclosed in Japanese Laid-Open Patent Publication No. 1077 and Japanese Patent Laid-Open No. 62-284578, there has been proposed a device for adjusting the light amount and potential of a predetermined pattern.

Further, in order to correct the gradation of the entire image forming apparatus, gamma correction by detecting a plurality of gradation pattern densities is disclosed in Japanese Patent Laid-Open Nos. 63-113568 and 63-208368. Gazette or Japanese Patent Laid-Open No. 63-21
No. 4077 is proposed.

On the other hand, in the above-mentioned method for controlling the toner density of the two-component developer, the image density control means optically detects the reference patch density developed on the photoconductor and the image density becomes constant. The method of controlling the toner supply based on the thus detected reference patch density is widely used without mentioning the preceding example. This method uses an optical sensor (hereinafter, also referred to as an ADC sensor) 64 as shown in FIG.
Is a method for measuring the density of the reference patch P formed on the photoconductor 27 and controlling the toner dispense so that the image density becomes constant based on the measured reference patch density.

As a modified example of this method, an ADC
A sensor and a sensor that detects the toner concentration in the developing unit (hereinafter also referred to as an ATC sensor) are used together and
JP-A-2-251865 and JP-A-2-251865 disclose a method in which toner dispense control is controlled by a DC sensor, and when the output of the ATC sensor exceeds a certain limit, the toner dispense control by the ADC sensor is changed or stopped.
It is proposed by Japanese Patent Laid-Open No. 262682 or Japanese Patent Publication No. 3-61947. However, these methods do not use the toner density detection result independently of the toner dispense control by the ADC sensor.

Further, correction of image forming conditions with a humidity sensor has been proposed, for example, in Japanese Patent Laid-Open Nos. 3-87859, 4-34563 and 63-33161. These are for changing the electric potential in order to correct the developing property change at the same toner density due to humidity.

[0011]

By the way, in the two-component development by the electrophotographic method, the developability of the medium / high density portion, that is, the medium / high density portion, depends on the number of copies, the operating time of the developing device or the environment such as humidity. It is known that the relationship between the image density and the toner density in a portion changes greatly.
As shown in FIG. 21, a medium / high concentration portion, for example, 60
The image density of% area ratio is particularly affected by humidity, and when the toner density is the same, generally the image density is high at high humidity and low at low humidity.
Relatively different depending on humidity.

On the other hand, as shown in FIG. 21, the effect of humidity is small at the image density of an extremely highlight portion, for example, 10% area ratio, and when the toner density is the same, an image is obtained at high humidity or low humidity. The concentration is almost unchanged.
As described above, the developability of the extremely highlighted portion with the same toner density does not change much in the environment such as the number of copies, the use time, the humidity, etc., unlike the medium / high density portion.

Therefore, the image density control means controls
If the toner dispense is controlled so that the image density in the high-density area does not change depending on the number of copies, the usage time of the developing device, the environment, etc., the toner density in the developing device will change. Changes in the image density of the extremely highlighted portion.
That is, if the image density in the middle / high density portion is made constant, the toner density becomes low at high humidity and the image density becomes extremely low at the extreme highlight portion, and conversely at high humidity the toner density becomes high and the extreme highlight portion becomes extremely high. The image density of the part becomes dark.

To explain this more specifically, if the toner density is controlled so that the 60% area ratio image density becomes the target of 1.25 in FIG. 21, the toner density becomes 6% when the humidity is 80%. Further, the toner concentration becomes 9.4% when the humidity is 30%. However, the 10% area ratio image density, which is the extreme highlight part at this time, is about 0.0 at high humidity.
While it is 16, it changes to about 0.04 when the humidity is low, resulting in a difference. As described above, this difference is a serious problem for the extreme highlight portion density difference because the sensitivity of the human eye is sensitive to the extreme highlight portion.

As described above, in the image forming apparatus that controls the toner density of the two-component developer by changing the toner density of the two-component developer in order to keep the image density of the middle / high density portions constant, the pulse width of the white level and the amount of light are different from the conventional ones. Or, even if the potential on the photoconductor is detected and the reproducibility of the extreme highlight is adjusted, there is a problem that the reproducibility of the extreme highlight portion changes.

As described above, in order to correct the gradation of the image forming apparatus as a whole, many methods have been proposed in which a plurality of gradation pattern densities are detected and gamma correction is performed. It is necessary to create or detect multiple patches to detect the gradation pattern density, which is not only time-consuming, but also requires a large amount of memory for the gamma correction data to correct the overall gradation. There is a problem that it will end up.

The present invention has been made in view of the above problems, and an object thereof is to change the toner density by controlling the toner dispense so that the density of the medium / high density portion becomes constant. Even so, it is an object of the present invention to provide a method for controlling extreme highlight reproduction of an image forming apparatus capable of reliably and easily obtaining stable extreme highlight reproducibility.

[0018]

In order to solve the above-mentioned problems, the invention according to claim 1 forms a light beam of multi-gradation digital image data on a uniformly charged photoreceptor. The latent image is developed with a two-component developer consisting of toner and carrier to form an image, and the image density control means optically detects the reference patch density developed on the photoconductor and the image density is constant. In the extreme highlight reproduction control method of the image forming apparatus for controlling the toner supply based on the detected reference patch density so that the medium / high density partial image density becomes constant by the image density control means. The toner supply is controlled based on the detected reference patch density, and the toner density of the two-component developer changed by the control of the toner supply is predicted by the toner density detecting means. Together with other measures, by the predicted or measured toner density, by using a developing adjustment means it is characterized by adjusting the ultrahighlight developability.

According to the second aspect of the invention, in order to adjust the developability of the extreme highlight, two or more of the developing bias, the charging and the exposure amount are changed so that the difference between the maximum density potential and the developing bias is changed. It is characterized in that the adjustment is made so that the difference between the lowest density potential and the developing bias changes without changing. Furthermore, the invention of claim 3 is characterized in that the developing property of the extremely highlighted portion is adjusted by adjusting the distance between the developing roll and the photoconductor.

Further, according to the invention of claim 4, a latent image formed by scanning a light beam by a signal obtained by gamma-correcting multi-tone digital image data on a uniformly charged photoreceptor is formed from toner and carrier. And a reference patch density developed on the photoconductor is optically detected by the image density control means and the detected reference is maintained so that the image density becomes constant. In an extreme highlight reproduction control method of an image forming apparatus for controlling toner supply based on patch density, based on the detected reference patch density so that the medium / high density partial image density is constant by the image density control means. The toner supply is controlled, and the toner density of the two-component developer changed by the toner supply control is predicted or measured by the toner density detecting means. To, by the predicted or measured toner density is characterized by changing the correction contents of the gamma correction using the gamma correction changing means.

Further, in the invention of claim 5, a latent image formed by scanning a uniformly charged photoconductor with a light beam by a signal obtained by gamma-correcting multi-tone digital image data is formed from toner and carrier. And a reference patch density developed on the photoconductor is optically detected by the image density control means and the detected reference is maintained so that the image density becomes constant. In an extreme highlight reproduction control method of an image forming apparatus for controlling toner supply based on patch density, based on the detected reference patch density so that the medium / high density partial image density is constant by the image density control means. The toner supply is controlled, and the toner concentration of the two-component developer changed by the control of the toner supply is predicted or measured by the toner concentration detecting means. Together, this predicted or measured toner density, by using a reference pattern adjustment means is characterized by adjusting the bias level and / or gain of the reference pattern.

Further, the invention of claim 6 uses a humidity sensor for measuring the humidity in the image forming apparatus, and predicts or measures the toner concentration based on the humidity in the image forming apparatus measured by the humidity sensor. It is characterized by doing.

Further, the invention of claim 7 is characterized in that the toner density is predicted or measured based on the usage time of the developing device or the number of times of image formation, which is related to the deterioration state of the developer.

Further, in the invention of claim 8, the toner concentration of the two-component developer in the developing device is predicted or measured based on the output of a toner concentration sensor which magnetically or optically measures the toner concentration. It is characterized by that.

[0025]

In the present invention thus constituted, the image density control means for optically detecting the reference patch density developed on the photoconductor to control the toner supply is used to detect the reference patch density based on the detected reference patch density. Medium / high density partial image density is controlled. Then, the toner density is changed by this control, and the changed toner density is predicted or measured by the toner density detecting means, and the developing property of the extreme highlight is adjusted by the developing property adjusting means by the predicted or measured toner density. To be done.

Therefore, the toner density is changed by controlling the toner supply in order to stabilize the medium / high density,
It is possible to easily control the fluctuation of the extreme highlight density reproduction caused by the change of the toner density without affecting the middle / high density portion.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of a color copying machine to which a first embodiment of an extreme highlight reproduction control method for an image forming apparatus according to the present invention is applied, and FIG. 2 is a block diagram of this color copying machine.

As shown in FIG. 1, the color copying machine 1 is roughly divided into a scanner section 4 for reading an original 3 (shown in FIG. 2) on an original table 2 and an image for processing image data read by the scanner section 4. A processing unit 5, a ROS optical unit 6 that drives a laser to emit a light beam in accordance with the image data processed by the image processing unit 5, and image formation that forms an image based on the light beam from the ROS optical unit 6. It is composed of a section 7.

As shown in FIG. 2, the scanner unit 4 includes an exposure lamp 8 for emitting irradiation light for irradiating the original 3, a CCD sensor 9 for reading reflected light of the irradiation light for irradiating the original 3, an amplifier 10, an A / D. The converter 11 includes a shading correction unit 12, a gap correction unit 13, and a density converter 14.

The image processing unit 5 is a basic image processing device 15 in a color copying machine such as color signal conversion and black reproduction (UCR) and MTF processing, a gamma correction means 16, a comparator 18, a triangular wave generator 19, and a triangular wave. The adjusting means 20, the patch signal generating means 58, and the selector 59 are included. The patch signal generation unit 58 creates and outputs patch image data for forming a toner reference patch image for controlling toner density on a photoconductor, which will be described later. The selector 59 selects analog image data at the time of normal copying, and when the arithmetic unit 52 of the image forming section 7 gives an instruction to make a patch, the patch signal generating means 58.
From the patch image data and sends the selected image data to the comparator 18. Then, the analog image data and the patch image data are binarized by the comparator 18. The patch signal generating means 58 also has a function of generating 100% image data for measuring the exposed portion potential when carrying out the photoreceptor potential control described later.

The ROS optical unit 6 includes a laser drive circuit 21, a laser 22, a laser light amount varying device 23 for variably controlling the laser light amount controlled by a computing device of the image forming unit 7 described later, a polygon mirror 24, and an fθ lens 2.
5 and the reflection mirror 26. The laser drive circuit 21 controls on / off of the laser 22 based on the binary image data sent from the comparator 18 and the laser light amount sent from the laser light amount varying device 23. The laser 22 emits a laser beam in response to an ON signal from the laser drive circuit 21.

As shown in FIGS. 1 and 2, the image forming section 7 further includes a photoconductor 27, a charging device 28, a rotary developing device 29, a transfer device 30, a cleaner device 31, a charge eliminating lamp 32, and a photoconductor 27. An electrometer 33 for measuring the electric potential,
A humidity sensor 34 for detecting the humidity in the image forming unit, a yellow developing device 35 that constitutes the rotary developing device 29, a magenta developing device 36, a cyan developing device 37, a black developing device 38, and a control signal from an arithmetic unit described later. And a transfer device 30 for controlling the toner supply to the rotary developing device 29 based on
Transfer drum 45, which also constitutes the transfer corotron 4
6, the peeling corotron 47, the static eliminating corotron 48, the fixing device 49, the paper conveying device 50, the paper tray 5
1. Arithmetic device 52 for controlling image formation, arithmetic device 5
From the charge amount varying device 53 that changes the charge amount of the charging device 28 controlled by 2, the developing bias varying device 54 that changes the developing bias, and the optical sensor 63 that measures the density of the reference patch developed on the photoconductor 27. It is configured.

In the color copying machine 1 configured as described above, the scanner unit 4 irradiates the original 3 with the irradiation light emitted from the exposure lamp 8, the reflected light is read by the CCD sensor 9, and the read signal is read. Amplifier 10
After being amplified to an appropriate level by the A / D converter 11, it is converted into 8-bit digital image data. Furthermore,
This digital image data is used for shading correction 12
After the gap correction 13 is performed, the density converter 14
Then, the reflectance data is converted into density data and sent to the image processing unit 5.

The density data sent to the image processing section 5 is further subjected to color signal conversion by the image processing device 15 of this image processing section 5,
Basic image processing in a color copying machine such as black reproduction (UCR) and MTF processing is performed, and converted into image data of four colors of yellow, magenta, cyan, and black. Next, this image data is subjected to gamma correction of each color gradation in accordance with the gradation of the image forming section 5 by the gamma correction means 16 and then converted from digital image data to analog image data by the D / A converter 17. Converted and selector 59
Sent to. Since the selector 59 selects analog image data during normal copying, this analog image data is sent to the comparator 18.

The analog image data sent to the comparator 18 is compared with the triangular wave signal of a predetermined cycle which is the reference pattern of the present invention sent from the triangular wave generator 19 through the triangular wave adjusting means 20 in the comparator 18 and pulsed. It is width-modulated and converted into binary image data. That is, as shown in FIG. 3, the analog image data (shown by a broken line) input in the comparator 18 is compared with a triangular wave (shown by a solid line), and a portion where the analog image data is larger than the triangular wave is " It is converted to binary image data (shown by a solid line) in which "0", that is, the laser is turned off, and the portion where the analog image data is smaller than the triangular wave is "1", that is, the laser is turned on. The triangular wave adjusting means 20 is adapted to adjust the bias for the triangular wave from the triangular wave generator 19 based on a control signal from an arithmetic unit of the image forming section 7 which will be described later. However, the present invention is not limited to this, and the same effect can be obtained even if the amplitude of the triangular wave is changed. Furthermore, in an image forming apparatus that reproduces images having different resolutions depending on the type of document such as characters and photographs, the bias amount can be adjusted for each resolution.

The converted binary image data is stored in the comparator 18
To the laser drive circuit 21 of the ROS optical section 6. The laser drive circuit 21 turns on / off the laser 22 based on the binary image data sent from the comparator 18.
Control. In this case, the output of the laser driving circuit 21 is controlled based on the variable control signal of the laser light amount from the laser light amount varying device 23 controlled by the control signal from the arithmetic unit of the image forming unit 7.

ON / OFF from the laser drive circuit 21
Based on the control signal, the laser 22 emits laser light, which is deflected by the polygon mirror 24 and further guided to the photoconductor 27 of the image forming unit 7 via the fθ lens 25 and the reflection mirror 26. Then, image formation is performed according to a well-known xerographic process. That is, after the rotating photoconductor 27 is uniformly negatively charged by the charging device 28, first, a black latent image of the first color is formed on the photoconductor 27 by the laser light from the ROS optical unit 6. . The formed latent image is developed by the black developing device 38 for the first color of the rotary developing device 29 in the portion written by the laser beam with the negatively charged black toner.

Next, the developed image is conveyed from the sheet tray 51 by the sheet conveying device 50 and transferred to the transfer drum 45.
Transfer to a sheet of paper (not shown) wrapped around
Is transferred from the photoconductor 27. Then, the toner image remaining on the photoconductor 27 without being transferred to the sheet is removed from the photoconductor 27 by the cleaner device 31, and the surface of the photoconductor 27 is neutralized by the static elimination lamp, and then the second color yellow Image formation follows. In that case, the second
The image formation of the yellow color is performed in the same manner as the image formation of the black color of the first color. When the image formation of the second color yellow is completed, the image formation of the third color magenta and the image formation of the fourth color cyan are sequentially performed in the same manner.
After the transfer of each color or the peeling of the paper, excess charges on the paper and on the film of the transfer drum 45 are discharged by the discharging corotron 48.

When the developed images of four colors are sequentially transferred to the paper on the transfer drum 45, the paper is peeled from the transfer drum 45 by the peeling corotron 47 and conveyed to the fixing device 49. The transfer image on the paper is fixed to form a color copy.

By the way, also in this embodiment, the image density control means optically detects the reference patch density developed on the photoconductor and detects the reference patch density so that the image density of the middle / high density portions becomes constant. The toner supply is controlled based on the patch density. This control will be described.

When the arithmetic unit 52 of the image forming section 7 issues a patch preparation instruction for each color to the patch signal generating means 58, the patch signal generating means 58 outputs a patch image data signal. The patch image data signal is selected by the selector 59 and sent to the comparator 18, and the comparator 18 binarizes the patch image data signal and outputs it to the laser drive circuit 21. Laser drive circuit 21
Controls on / off of the laser 22 based on the binary image data signal from the comparator 18, whereby the laser 22 emits a laser beam. This laser light is the photoconductor 2
The latent image of the reference patch image is formed on the photoconductor 27 by being guided to the image forming member 7, and the latent image is developed by the developing device of the corresponding color to form the reference patch image. Then, the optical sensor 63 optically reads the density of the developed reference patch image on the photoconductor 27 and outputs the reference patch image density signal to the arithmetic unit 52. The arithmetic unit 52 is
The toner dispense device 43 of the corresponding color is driven and controlled based on the reference patch image density signal so that the toner supply from the toner dispense device 43 becomes constant in the medium / high image density based on the reference patch density. Controlled.

If the toner supply is controlled so that the medium / high image density becomes constant, the image density of the extreme highlight portion changes as a result, so that the image density of the extreme highlight portion does not change. Extreme highlight reproduction control is performed as described above.

Next, a first embodiment of this extreme highlight reproduction control method will be described by applying it to the color copying machine 1. In the present embodiment, when the toner supply is controlled so that the medium / high image density becomes constant, the toner density changes depending on the humidity inside the image forming section 7. Is detected, and the changed toner density is predicted based on the detected humidity in the image forming unit 7. Then, based on the predicted toner density, the developing property adjusting means adjusts the image density of the extremely highlighted portion of the image.

This will be described more specifically. First, in the present embodiment, for example, as shown in FIG. 4, the toner density required to obtain the 60% area ratio target image density, 6 at that time.
The relationship between image density and humidity at 0% and 10% area ratio is used.

The extreme highlight reproduction control method of this embodiment is performed using the relationship shown in FIG. 4 and the flow shown in FIG. First, each process of the flow shown in FIG. 5 is performed when the power of the image forming apparatus is turned on. It should be noted that it may be carried out not only when the power is turned on, but also periodically.

After the power is turned on, it is determined in step S1 whether or not the power is turned on, and if it is determined that the power is turned on, the humidity sensor 34 determines the humidity in the image forming unit 7 in step S2. To be measured. If it is determined that the power is not turned on, the process of step S1 is repeated.

When the humidity in the image forming section 7 is measured in step 2, whether the humidity measured in step S3 is 40% or less, or between 40% and 70%, or 7
The arithmetic unit 52 determines whether it is 0% or more. When it is determined in step S4 that the humidity is 40% or less, the triangular wave adjusting unit 20 sets the triangular wave bias to a negative value, and when it is determined that the humidity is between 40% and 70%, the triangular wave is set. When the adjusting means 20 sets the triangular wave bias to zero (0) and further determines that the humidity is 70% or more, the triangular wave adjusting means 20 sets the triangular wave bias to positive.

FIG. 6 is a diagram for explaining the operation of this triangular wave bias. As shown in FIG. 6, when the triangular wave adjusting means 20 applies a positive bias to the triangular wave from the triangular wave generator 19, the width of the pulse output from the comparator 18 for the same analog image data becomes wider. Therefore the same 10%
The amount of laser light is larger than the image data of the area ratio,
As a result, the density developed is high. On the contrary, when a negative bias is applied to the triangular wave from the triangular wave generator 19 by the triangular wave adjusting means 20, the pulse width output from the comparator 18 is narrowed, and thus the developed density is thin. In FIG. 6, when the bias amount for the triangular wave is adjusted, the overall pulse width from the white level to the black level, that is, the laser light amount is significantly changed,
These descriptions are because the bias amount is drawn large in order to make the operation of the triangular wave bias easy to understand, and the actual bias is extremely small compared to the entire triangular wave amplitude. In addition, as shown in FIG. 7, the highlight portion, which is the low image area ratio portion, has a larger pulse width, that is, the potential change amount of the photoconductor 27 with respect to the change in the light amount, and as described above, the human eye is on the highlight side. In comparison with the high density side, the density change is slower. Therefore, in the bias adjustment range of the present embodiment, the density change on the medium / high density side is hardly noticed when adjusting the density of the highlight portion.

Then, the binarized image signal output from the comparator 18 is adjusted by the triangular wave bias set in step S4, and the laser drive circuit 21 causes the laser 22 to output the laser 22 based on the adjusted binarized image signal. Control the on / off time of the. As a result, the density of the extreme highlight portion of the latent image formed on the photoconductor 27 is adjusted, and as a result, the image density of the extreme highlight portion is adjusted.

Thus, in the first embodiment, the toner density in the developing unit is predicted based on the humidity in the image forming section 7 measured by the humidity sensor 34, and the triangular wave is adjusted based on the predicted toner density. By controlling the on / off time of the laser 22, the laser light for the image data of 10% area ratio, which is the extremely highlighted portion, is controlled, and the image density of 10% area ratio is adjusted. In that case, the comparator 18, the triangular wave adjusting means 20, the laser driving circuit 21, the laser light amount varying device 23, and the computing device 52.
This constitutes the developing property adjusting means used in the present invention. Further, the humidity sensor 34 constitutes a toner concentration detecting means used in the present invention.

FIG. 8 is a diagram showing a second embodiment of the present invention. The same components as those in the first embodiment described above are designated by the same reference numerals, and detailed description thereof will be omitted. In the second embodiment, the gamma correction means 16 is included in the image processing unit 5.
A gamma correction changing means 55 connected to is provided. The gamma correction changing unit 55 selects and selects a plurality of correction tables 56 in which different gamma correction contents are stored and a gamma correction content correction table 56 based on an instruction signal from the arithmetic unit 52 of the image forming unit 7. The gamma correction means 16 according to the corrected correction table 56.
And a first selector 57 for changing the gamma correction content of. Then, the arithmetic unit 52 of the image forming unit 7
The gamma correction content of the gamma correction means 16 is changed in response to the instruction signal.

Further, similar to the first embodiment, the image processing section 5 has patch signal generating means 58 and D for generating toner patch image data for density control on the photoconductor 27.
The second selector 5 which selects one of the analog image data from the A / A converter 17 and the patch image data from the patch signal generating means 58 and sends it to the comparator 18.
9 and are provided. The second selector 59 also selects analog image data during normal copying, and selects patch image data from the patch signal generating means 58 when the processor 52 of the image forming section 7 gives an instruction to create a patch. , Respectively, to the comparator 18. Similarly, the density of the toner patch image data formed on the photoconductor 27 is measured by the optical sensor 63.

In the second embodiment, the triangular wave adjusting means 20 in the first embodiment is omitted.

The extreme highlight reproduction control method of the second embodiment is the same as that of the above-described first embodiment shown in FIG.
The relationship between the humidity characteristic of the toner density and the highlight density for obtaining the area ratio target image density and the flow shown in FIG. 9 are used. First, each processing of the flow shown in FIG. 9 is performed when the power of the image forming apparatus is turned on. It should be noted that it may be carried out not only when the power is turned on, but also periodically.

As shown in FIG. 9, step S1 is performed after the power is turned on.
Then, it is determined whether or not the power is turned on, and if it is determined that the power is turned on, the humidity sensor 34 measures the humidity in the image forming unit 7 in step S2. If it is determined that the power is not turned on, the process of step S1 is repeated.

When the humidity in the image forming section 7 is measured in step 2, whether the humidity measured in step S3 is 40% or less, or between 40% and 70%, or 7
The arithmetic unit 52 determines whether it is 0% or more. Then, when it is determined in step S4 that the humidity is 40% or less, the arithmetic unit 52 causes the first gamma correction changing unit 55 to operate.
A selection signal is output to the selector 57, and the first selector 57 selects the high TC gamma correction table 56a,
When it is determined that the humidity is between 40% and 70%, the first selector 57 similarly selects the standard TC gamma correction table 56b, and when it is determined that the humidity is 70% or more, The first selector 57 selects the low TC gamma correction table 56c.

FIG. 10 is a diagram for explaining typical three contents of these gamma correction tables. In FIG. 10, (1) is a gamma correction table for standard TC,
(2) is a high TC gamma correction table, and (3) is a low TC gamma correction table. Of course, two or four or more gamma correction tables may be provided. Further, it is not necessary to have a plurality of gamma correction tables over the entire gradation, and it is possible to have only a highlighted portion.

FIG. 11 shows the color copying machine 1 using the standard T
FIG. 12 is a diagram showing the gradation property when gradation correction is not performed when the middle / high density portion is adjusted to the target at C (humidity 40% to 70%). FIG. It is a figure which shows the target gradation. That is, the standard TC shown in FIG.
When the gamma correction is performed using the standard TC gamma correction table shown in FIG. 10A, the target gradation shown in FIG. 12 is obtained.

Therefore, if the correction table of (2) of FIG. 10 is selected at S4 when the humidity is low (when the toner concentration is high; when the toner TC is high), the final gradation is the target floor of FIG. The result is almost equal to the tonality. Similarly, if the correction table of FIG. 10 (3) is selected at the time of high humidity (at the time of low TC), the final gradation is almost equal to the target gradation shown in FIG. To be

Then, the on / off time of the laser 22 is controlled by adjusting the contents of gamma correction using the gamma correction table selected in step S4. As a result, the density of the extreme highlight portion of the latent image formed on the photoconductor 27 is adjusted, and as a result, the image density of the extreme highlight portion is adjusted.

Thus, in the second embodiment, the arithmetic unit 52 predicts the toner density in the developing device based on the humidity in the image forming section 7 measured by the humidity sensor 34,
By changing the gamma correction content of the gamma correction means 16 based on the predicted toner density and controlling the on / off time of the laser 22, the extreme highlight portion 10 is obtained.
Laser light for image data of% area ratio is controlled,
The image density of 10% area ratio is adjusted.

FIG. 13 is a diagram showing a third embodiment of the present invention. The same components as those of the first and second embodiments described above are designated by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 13, in the third embodiment, only the patch signal generating means 58 is provided without providing the gamma correction changing means 55 in the second embodiment. Also in the third embodiment, the selector 59 selects analog image data at the time of normal copying, and when the arithmetic unit 52 of the image forming section 7 gives an instruction to make a patch, the patch signal generating means 58 outputs the patch. Image data is selected and sent to the comparator 18, respectively. Then, the analog image data and the patch image data are binarized by the comparator 18, respectively.

In the third embodiment, color copying is performed by an instruction signal from the arithmetic unit 52 of the image forming unit 7 before the copying is started immediately after the color copying machine 1 is turned on and after the lapse of every 30 minutes thereafter. The potential of the photoconductor 27 of the machine 1 is controlled. Note that, of course, the present invention is not limited to this, and the potential control of the photoconductor 27 may be performed during copying or the like in accordance with the sensitivity variation characteristic of the photoconductor 27 to be used.

FIG. 14 is a diagram showing a flow of processing for controlling the potential of the photoconductor 27. The potential control of the photoconductor 27 is performed according to the flow shown in FIG. 14, but before the respective processes are performed, the target dark potential VHS, the target exposure partial potential VLS, and the target dark potential VHS to the development bias potential VB are preset. The anti-fogging potential difference VC up to is stored in the arithmetic unit 52 of the image forming unit 7.

First, in step S1, the dark potentials VH1 and VH2 when the grid voltage of the charging device 28 is changed to VG1 and VG2 by the charge amount varying device 53 are detected by the electrometer 33. Next, in step S2, the detected dark potentials VH1 and VH
Using H2 and the grid voltages VG1 and VG2, the grid voltage VGS for obtaining the target dark potential VHS is calculated by the following formula.

VGS = (VG2−VG1) × (VHS−VH1) / (VH2−VH1) + VG1 Next, the obtained grid voltage VGS is used to charge the photoconductor 27 in step S3. Then, the arithmetic unit 52
The selector 59 of the image processing unit 5 selects 100% image data from the patch signal generator 58 in response to the instruction signal from and sends it to the comparator 18. The comparator 18 compares the 100% image data with the triangular wave from the triangular wave generator 19 and outputs 2
The laser driving circuit 2 of the ROS optical unit 6 converts the digitized data
Send to 1. On the other hand, the laser light amount varying device 23 drives the laser drive circuit 21 with two kinds of laser light amounts LD1 and LD2 to create a patch of 100% image data on the two kinds of laser light amounts LD1 and LD2 on the photoconductor 27. , The bright potentials VL1 and VL2 of the exposed portions are detected by the electrometer 33.

Next, in step S4, the laser light amount LDS for obtaining the target bright potential VLS is calculated by the following equation. LDS = LD2-(LD2-LD1) × (VLS-VL2) / (VL1 −
VL2) Next, in step S5, the development bias potential VB is obtained by subtracting the fog prevention potential difference VC from the target dark potential VHS, and then in step S6, the arithmetic unit 52 controls the charge amount varying device 53 to generate the grid voltage VGS.
By controlling the laser light amount varying device 23, the laser light amount LDS, and the developing bias varying device 5
4, the developing bias potential VB is set, and the potential control of the photoconductor 27 ends.

In the third embodiment, by adjusting the output of the humidity sensor 34 of the image forming section 7, that is, the humidity in the image forming section 7, two or more of the developing bias, the charging and the exposure are adjusted to an extremely high level. The image density of the light part is adjusted.

The extreme highlight reproduction control method of the third embodiment is similar to the first and second embodiments described above and shown in FIG. 4, the humidity characteristic of the toner density for obtaining the 60% area ratio target image density. And the highlight density and the flow shown in FIG. First, each process of the flow shown in FIG. 15 is performed when the power of the image forming apparatus is turned on.
It should be noted that it may be carried out not only when the power is turned on, but also periodically.

As shown in FIG. 15, step S after power is turned on.
In 1, it is judged whether the power is turned on from off,
When it is determined that the power is turned on, the humidity sensor 34 measures the humidity in the image forming unit 7 in step S2. If it is determined that the power is not turned on, the process of step S1 is repeated.

When the humidity in the image forming section 7 is measured in step 2, the correction amount α proportional to the humidity is obtained from FIG. 16 in step S3. Then, in S4, the correction amount α is added to the target dark potential VHS and the fog prevention potential difference VC in the photoconductor potential control of FIG. 14 to update the target dark potential VHS and the fog prevention potential difference VC. After that, the photoconductor potential control is performed according to the flowchart shown in FIG. As a result, the target exposure partial potential VLS is constant, and the target dark potential VHS and the fog prevention potential difference V
Since both C increase by the correction amount α, the developing bias potential VB does not change. Therefore, the grid voltage VGS and the laser light amount LD are set so that the difference between the exposed portion potential corresponding to the maximum density and the developing bias does not change, and only the difference between the dark potential corresponding to the minimum density and the developing bias changes.
This means that S and the developing bias potential VB have been adjusted.

Here, the image density is generally determined by the difference between the potential of the image portion and the developing bias potential VB from the highlight to the entire high density. Especially, the highlight portion corresponds to the minimum density (white background). It is known that it changes depending on the difference between the dark potential and the developing bias, that is, the fog prevention potential difference. As shown in FIG. 17, when the difference between the potential of each image portion and the developing bias potential is constant, the image density due to the fog prevention potential difference changes only in the extremely highlighted portion.

As described above, the toner density is predicted or measured according to the humidity, and only the difference between the dark potential and the developing bias corresponding to the minimum density is maintained without changing the difference between the exposed portion potential corresponding to the maximum density and the developing bias. As it changes, grid voltage VGS, laser light amount LDS, development bias potential VB
By adjusting, the extreme highlight patch image density can be adjusted to a desired density without affecting the middle / high density portions. Also in the third embodiment, substantially the same effects as those of the above-mentioned first and second embodiments can be obtained.

FIG. 18 is a schematic view of a developing device used in the fourth embodiment of the present invention. As shown in FIG. 18, the distance (DRS: D) between the photoconductor 27 and the developing roller 60 of each developing device is set.
A distance adjusting device 6 capable of changing the “run to Roll Space” by adjusting the distance between the reference plate 61 fixed at a predetermined position of the rotary developing device 29 and the developing device.
2 is provided. In the above-mentioned third embodiment, the grid voltage VGS, so that only the difference between the dark potential corresponding to the minimum density and the developing bias is changed without changing the difference between the exposed portion potential corresponding to the maximum density and the developing bias. Although the laser light amount LDS and the developing bias potential VB are adjusted to adjust the extreme highlight patch image density, in the fourth embodiment, by adjusting the distance between the photoconductor 27 and the developing roll 60, the extreme high patch image density is adjusted. The density of the light patch image is adjusted.

As shown in FIG. 19, the density of the extreme highlight patch image changes depending on the distance between the photoconductor 27 and the developing roll 60. In that case, the smaller the DRS, the more the extreme highlight is scratched and thinned by the developer on the developing roll 60. Therefore, by adjusting the distance between the photoconductor 27 and the developing roller 60, the same effects as those of the first to third embodiments described above can be obtained.

At this time, the densities on the medium / high density side also slightly change, and the smaller the DRS, the stronger the developing electric field and the higher the density. However, the change in the density of the highlight part is larger than that of the middle / high density side, and as described above, the human eye is more blunt on the high density side than on the highlight side. In the light reproducibility adjustment range, such a density change on the medium / high density side is not annoying.

The present invention is not limited to the above-mentioned respective embodiments, but instead of predicting the toner density based on the humidity, the toner density is predicted based on the number of copies or the usage time of the developing device, and the extreme highlight portion The image density may be adjusted.
This is because, in general, as the developer deteriorates, the toner density required to keep the medium-high density constant becomes lower.
The toner density can be predicted by the deterioration of the developer.

Further, as shown in FIG. 20, the toner concentration sensors 39, 40, 41, 42 for the respective colors are provided near the agitating / conveying roll 64 in the developing devices 35, 36, 37, 38, respectively. Toner concentration sensor 39, 40, 4
1, 42, the toner density in the developing device is periodically measured, and the arithmetic unit 52 can also adjust the image density in the extreme highlight portion based on the measured toner density.
With this toner concentration sensor, the toner concentration can be detected more accurately, and therefore more accurate extreme highlight control can be performed.

[0080]

As is apparent from the above description, according to the present invention, even if the toner supply is controlled in order to keep the image density of the middle / high density portions constant, the extreme highlight density reproduction that occurs It becomes possible to easily control the fluctuation of the value without affecting the middle / high concentration part. This makes it possible to easily and surely obtain stable extreme highlight density reproducibility.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a color copying machine to which a first embodiment of an extreme highlight reproduction control method of an image forming apparatus according to the present invention is applied.

FIG. 2 is a block diagram of this color copying machine.

FIG. 3 is a diagram illustrating binarization of image data by pulse width modulation.

FIG. 4 is a diagram showing a relationship between a humidity characteristic of a toner density and a highlight density for obtaining a 60% area ratio target image density.

FIG. 5 is a diagram showing a flow of processing of the first embodiment of the present invention.

FIG. 6 is a diagram illustrating an operation of a triangular wave bias.

FIG. 7 is a diagram showing a potential change amount of a photoconductor when a pulse width corresponding to 2% is adjusted by an image area ratio.

FIG. 8 is a block diagram of a color copying machine similar to that of FIG. 2 to which a second embodiment of the present invention is applied.

FIG. 9 is a diagram showing a flow of processing of a second embodiment of the present invention.

FIG. 10 is a diagram showing the contents of a correction table used in the flow of the second embodiment.

FIG. 11 is a diagram showing a gradation property when gradation correction is not performed in standard TC of a color copying machine.

FIG. 12 is a diagram showing target gradation of a color copying machine.

13 is a block diagram of a color copying machine similar to that of FIG. 2, to which a third embodiment of the present invention is applied.

FIG. 14 is a diagram showing a flow of processing for controlling the potential of the photoconductor in the third embodiment of the present invention.

FIG. 15 is a diagram showing a flow of processing of a third embodiment.

FIG. 16 is a diagram showing the relationship between the correction amount α and humidity used in the flow of the third embodiment.

FIG. 17 is a diagram showing the relationship between the fog prevention potential difference and the image density in the third embodiment.

FIG. 18 is a diagram showing a photoconductor and a developing device of a color copying machine to which a fourth embodiment of the present invention is applied.

FIG. 19 is a diagram for explaining changes in reproducibility of extreme highlights by extreme highlight control according to the fourth embodiment.

FIG. 20 is a diagram showing a developing device provided with a conventional toner concentration sensor.

FIG. 21 is a diagram showing a change in developability due to humidity.

FIG. 22 is a diagram illustrating the measurement of the density of a toner patch on a photoconductor using an optical sensor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Color copying machine, 2 ... Original platen, 3 ... Original, 4 ... Scanner part, 5 ... Image processing part, 6 ... ROS optical part, 7 ... Image forming part, 8 ... Exposure lamp, 9 ... CCD sensor, 10 ... Amplifier, 11 ... A / D converter, 12 ... Sewing correction means, 13 ... Gap correction means, 14 ... Density converter, 1
5 ... Basic image processing device in color copying machine for color conversion, 16 ... Gamma correction means, 17 ... D / A converter, 1
8 ... Comparator, 19 ... Triangular wave generator, 20 ... Triangular wave adjustment generator, 21 ... Laser drive circuit, 22 ... Laser, 23
... Laser light amount variable device, 24 ... Polygon mirror, 25
... fθ lens, 26 ... reflective mirror, 27 ... photoconductor, 28
... charging device, 29 ... rotary developing device, 30 ... transfer device, 31 ... cleaner device, 32 ... static elimination lamp, 33 ...
Electrometer, 34 ... Humidity sensor, 35 ... Yellow developing device,
36 ... Magenta developing device, 37 ... Cyan developing device, 38 ... Black developing device, 39, 40, 41, 42 ... Toner density sensor, 43 ... Toner dispensing device, 44 ... Toner density reference value changing means, 45 ... Transfer drum, 46 ... Transfer corotron, 47 ... Peeling corotron, 48 ... Static elimination corotron, 49 ... Fixing device, 50 ... Paper transport device, 51 ... Paper tray, 52 ... Arithmetic device, 53 ... Charge amount varying device, 54
... development bias varying device, 55 ... gamma correction changing means,
56 ... Correction table, 57 ... First selector, 58 ... Patch signal generating means, 59 ... (Second) selector, 60 ...
Developing roll, 61 ... Reference plate, 62 ... Distance adjusting device, 63
… Optical sensor, 64… Agitation / conveyance roll

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location G03G 15/06 101 H04N 1/407

Claims (8)

[Claims] 1. A latent image formed by scanning a light beam of multi-gradation digital image data on a uniformly charged photoreceptor is developed with a two-component developer consisting of toner and carrier to form an image. In addition, the image density control means optically detects the medium or high density reference patch density developed on the photoconductor and supplies toner based on the detected reference patch density so that the image density becomes constant. In the extreme highlight reproduction control method of the image forming apparatus, the toner density is controlled by the image density control means based on the detected reference patch density so that the medium / high density partial image density becomes constant, and The toner concentration of the two-component developer changed by the control of the toner supply is predicted or measured by the toner concentration detection means, and this prediction or measurement is performed. By the toner concentration, ultrahighlight reproduction control method for an image forming apparatus characterized by adjusting the ultrahighlight developability with a developer adjustment means. 2. In order to adjust the developability of the extreme highlight, two or more of the developing bias, the charging, and the exposure dose are set.
Without changing the difference between the maximum density potential and the developing bias,
2. The extreme highlight reproduction control method for an image forming apparatus according to claim 1, wherein the difference between the lowest density potential and the developing bias is adjusted so as to change. 3. The extreme highlight reproduction of the image forming apparatus according to claim 1, wherein the developing property of the extreme highlight portion is adjusted by adjusting the distance between the developing roll and the photoconductor. Control method. 4. A latent image formed by scanning a light beam according to a signal obtained by gamma-correcting multi-gradation digital image data on a uniformly charged photoreceptor is developed with a two-component developer consisting of toner and carrier. And form an image, and the image density control means optically detects the medium or high density reference patch density developed on the photoconductor and detects the reference patch density so that the image density becomes constant. In the extreme highlight reproduction control method of the image forming apparatus for controlling the toner supply based on the above, the toner supply based on the detected reference patch density so that the medium / high density partial image density becomes constant by the image density control unit. And the toner concentration of the two-component developer changed by the control of the toner supply is predicted or measured by the toner concentration detecting means. The predicted or measured toner concentration, ultrahighlight reproduction control method for an image forming apparatus and changes the correction contents of the gamma correction using the gamma correction changing means. 5. A multi-gradation digital image data is converted into an analog signal, a reference pattern of a predetermined cycle is compared with the analog signal, and a light beam by a pulse width modulated binarized signal is made uniform. The latent image formed by scanning on the charged photoconductor is developed with a two-component developer consisting of toner and carrier to form an image, and the medium or high density developed on the photoconductor by the image density control means. In the extreme highlight reproduction control method of the image forming apparatus, wherein the reference patch density is optically detected and the toner supply is controlled based on the detected reference patch density so that the image density becomes constant. The toner supply is controlled based on the detected reference patch density so that the medium / high density partial image density becomes constant, and the toner supply is changed by this toner supply control. The toner density of the two-component developer is predicted or measured by the toner density detecting means, and the bias level and / or gain of the reference pattern is adjusted by the reference pattern adjusting means according to the predicted or measured toner density. An extreme highlight reproduction control method for an image forming apparatus, comprising: 6. A toner sensor for measuring the humidity in the image forming apparatus is used, and the toner density is predicted or measured based on the humidity in the image forming apparatus measured by the humidity sensor. Item 6. An extreme highlight reproduction control method for an image forming apparatus according to any one of items 1 to 5. 7. The toner density is predicted or measured based on the usage time of the developing device or the number of times of image formation related to the deterioration state of the developer. Extreme highlight reproduction control method for image forming apparatus. 8. The toner concentration is predicted or measured based on the output of a toner concentration sensor that magnetically or optically measures the toner concentration of the two-component developer in the developing device. 6. An extreme highlight reproduction control method for an image forming apparatus according to any one of 1 to 5.