JPH05313453A - Image forming device - Google Patents

Abstract

PURPOSE:To realize an image forming device where faithful reproducibility is obtained even in the case of an original having half tone density such as a photograph. CONSTITUTION:In a copying machine having a photographic mode, toner images for detection 16 and 18 are formed on the surface of a photosensitive drum 1, and image forming process conditions such as electrostatic charging potential, exposure, and developing bias are changed by a CPU 6 based on the density of the toner images for detection 16 and 18 detected by a P (density) sensor 5. It is good to use patterns for detection 15 and 17 having the different ratio of toner adhering area to the entire area as a pattern for detection and change at least the electrostatic charging potential when the density of the toner image for detection 16 having the large ratio is thicker than reference density. It is also good to change at least the exposure when the density of the toner image for detection 18 having the small ratio is thinner than the reference density. It is conceivable to set the plural photographic modes corresponding to the number of the lines of the original and use the pattern for detection having the different number of lines corresponding to the respective photographic modes.

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 such as a copying machine, a facsimile or a printer, and more particularly to an image forming apparatus capable of obtaining faithful reproducibility even in a halftone density original such as a photograph. is there.

[0002]

2. Description of the Related Art Conventionally, in a copying machine using this type of electrophotographic process, since the emphasis is placed on copying general office documents, it is possible to make a copy having a relatively high density even for a document having a low density. However, there is a drawback in that faithful reproducibility cannot be obtained in an original designed to obtain a large amount of halftone density such as a photograph.

Therefore, in order to solve this drawback, it is known to provide a halftone image forming mode (hereinafter referred to as a photographic mode) for setting an image forming process condition suitable for an original having a large amount of halftone density such as a photograph. Has been. When this photo mode is selected, the image forming process conditions (charging potential, exposure amount, developing bias, etc.) are fixed to the predetermined image forming process conditions that are suitable for reproducing originals with high halftone density such as photographs. Is set. For this reason, in the conventional image formation in the photographic mode, it is not possible to control the density according to the difference in the number of lines of the document or the state of the apparatus (change over time such as deterioration of the image carrier, influence of environmental change). , An image having a large ratio of the area where toner adheres to the entire area of the image pattern (hereinafter, referred to as black area ratio) causes image deterioration such as dot crushing and line crushing, and an image having a small black area ratio, The phenomenon that the image is not reproduced occurs. Therefore, since it is not possible to obtain the density reproducibility corresponding to the original, that is, the appropriate dot reproducibility and line reproducibility, it is impossible to obtain the faithful reproducibility of the original with the halftone density even if the above photo mode is selected. The problem remained.

In order to solve the above problem, it is known to detect the line width of an image pattern, compare it with a reference value, and set image forming process conditions based on the comparison result (for example, See Japanese Patent Application Laid-Open No. 2-308186).

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its object is to:
An object of the present invention is to provide an image forming apparatus capable of obtaining faithful reproducibility even in an original having a halftone density such as a photograph.

[0006]

In order to achieve the above-mentioned object, the invention of claim 1 provides a charging means for uniformly charging the surface of an image carrier, and an electrostatic latent image on the surface of the image carrier by optical writing. And an developing means for forming a toner image corresponding to the electrostatic latent image on the surface of the image bearing member are provided, and the image forming process conditions for reproducing the halftone density image are applied. In an image forming apparatus having a halftone image forming mode set in advance, a toner density detecting means for detecting the toner adhesion amount of the toner image is provided, and a detection pattern corresponding to a predetermined detection pattern is provided on the surface of the image carrier. And a control unit for changing the image forming process condition on the basis of the density of the toner image for detection detected by the toner density detecting unit.

The invention according to claim 2 is characterized in that, as the detection pattern, a plurality of detection patterns having different ratios of the toner adhesion area to the entire area of the detection pattern are used. ..

According to a third aspect of the invention, when the density of the detection toner image corresponding to the detection pattern having the large ratio is higher than a preset reference density, at least the charging potential of the charging means is changed. It is characterized in that a control means for controlling is provided. For example, at least a control unit that lowers the charging potential of the charging unit is provided.

Further, according to the invention of claim 4, when the density of the detection toner image corresponding to the detection pattern having the small ratio is lower than a preset reference density, it is easy to control the density of the low density portion. It is characterized in that a control means for changing at least the exposure amount by the exposure means is provided. For example, a control means for reducing at least the exposure amount of the exposure means is provided.

According to a fifth aspect of the present invention, a plurality of the halftone image forming modes are set according to the type of the original, and the detection patterns of different types corresponding to the respective halftone image forming modes are set. Is used. For example, a plurality of halftone image forming modes are set according to the difference in the number of lines of the document, and the detection patterns having different numbers of lines are used in correspondence with the respective halftone image forming modes.

[0011]

According to the invention of claim 1, the detection toner image corresponding to the predetermined detection pattern, for example, the detection pattern having a predetermined density, is formed and detected by the toner density detecting means. Control means is provided for changing the image forming process conditions based on the density of the detection toner image. As a result, when the reproducibility of the image density is changed due to the change with time such as the deterioration of the image carrier or the change in the environment, the change is corrected so that the image density is not changed. The process conditions, for example, the charging potential, the exposure amount, the developing bias voltage, etc. are changed and set.

According to the second aspect of the present invention, as the detection pattern, a plurality of detection patterns having different ratios of the toner adhesion area to the entire area of the detection pattern are used. Accordingly, the detection patterns having different ratios can be used for density control in the image regions corresponding to the respective ratios. For example, the detection pattern having a large ratio can be used for density control in an image region having a large ratio, and the detection pattern having a small ratio can be used for density control in an image region having a small ratio.

In a third aspect of the invention, when the density of the detection toner image corresponding to the detection pattern having the large ratio is higher than a preset reference density,
At least the charging potential of the charging means is changed. As a result, the document density in the image area having the large ratio is faithfully reproduced. For example, as shown in FIG. 2, by lowering the charging potential, the curve (i) in the state before the change is changed to the curve (j), and the document density reproduction width in the high density portion starts from the right end of C in the figure. It spreads to the right end of C '.

According to a fourth aspect of the present invention, when the density of the detection toner image corresponding to the detection pattern having the small ratio is lower than a preset reference density,
At least the exposure amount by the exposure means is changed. As a result, the original density in the image area having the smaller ratio is faithfully reproduced. For example, as shown in FIG. 2, the curve (j) before the change is changed to the curve (k) by decreasing the exposure amount, and the document density reproduction width in the low density portion is the left end of C ′ in the drawing. To the left end of C ''.

According to the invention of claim 5, the type of original,
For example, a plurality of the halftone image forming modes are set according to the difference in the number of lines, and the detection patterns of different types, for example, different line numbers are used in correspondence with the respective halftone image forming modes. As a result, even when the reproducibility of the image density changes due to the influence of the document type, for example, the difference in the number of lines, the change in the image forming process condition Charge potential, exposure dose,
The developing bias voltage and the like are changed and set.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter referred to as a copying machine) which is an image forming apparatus will be described below. FIG. 1 is a schematic configuration diagram of a copying machine according to this embodiment. The photoconductor drum 1, which is an image carrier, rotates in the direction of the arrow and is uniformly primary-charged by a charger 2 that is a charging unit. The image exposure light from the digital optical system 3 which is the exposure means driven by the image signal is the photosensitive drum 1.
It is irradiated onto and an electrostatic latent image is formed. This electrostatic latent image is developed by the developing roller 41 to which the bias voltage of the developing device 4 which is the developing means is applied, and becomes a visible image. The visible image is transferred onto the transfer paper 10 by the transfer charger 11. The transfer paper 10 has the transferred visible image fixed by a fixing device (not shown) and is discharged to the outside of the machine. The toner remaining on the photosensitive drum 1 without being transferred is cleaned by the cleaning device 12. The residual charges on the photosensitive drum 1 after the cleaning are removed by the static eliminator 13 to prepare for the next image formation.

In order to detect the amount of toner adhered on the surface of the photosensitive drum 1, the developing device 4 around the surface of the photosensitive drum 1 is used.
A toner image density sensor (hereinafter, referred to as a P sensor) 5 utilizing light reflection is provided at a position close to the surface of the photoconductor drum 1 on the downstream side of the above, facing the surface of the photoconductor drum 1. The output value of the P sensor 5 determines the amount of toner adhered on the surface of the photosensitive drum 1.

Further, in this embodiment, there is provided means for selecting a photographic mode for setting an image forming process condition for a document such as a photograph having a large halftone density. By the way, when this photographic mode is selected, it is designed so as to be set to a predetermined constant image forming process condition (charging potential, exposure amount, developing bias, etc.). It was not possible to control the density according to the state of the machine (time-dependent changes such as deterioration of the image bearing member, influence of environmental changes). Therefore, for example, in an image with a large black area ratio, image deterioration such as dot crushing and line crushing occurs, and with a small black area ratio, an image cannot be reproduced.

Therefore, in the first embodiment, the detection pattern 15 having a large black area ratio and the detection pattern 17 having a small black area ratio are previously attached to the non-image area 14 of the contact glass. Hereinafter, description will be given along the control flowchart of FIG. First, when the photo mode is selected in step 1 and the copy button is pressed in step 2, in step 3, the detection toner image 16 corresponding to the detection pattern 15 having a large black area ratio is formed on the photosensitive drum 1.
Formed on the surface. Next, in step 4, the toner adhesion amount of the detecting toner image 16 is detected by the P sensor, and in step 5, the comparison between the density of the detecting toner image 16 and a preset density reference value is a control / arithmetic unit. Performed by the CPU 6. When the density of the detection toner image 16 corresponding to the detection pattern 15 having a large black area ratio is higher than the density reference value, in step 6, for example, the CPU 6 causes the charging high-voltage power supply 9 to lower the charging potential. To control.

Next, in step 7, a detection toner image 18 corresponding to the detection pattern 17 having a small black area ratio is formed on the surface of the photosensitive drum 1. Then in step 8,
The toner adhesion amount of the detection toner image 18 is detected by the P sensor, and in step 9, the density of the detection toner image 18 is compared with a preset density reference value by the CPU 6 which is a control / calculation unit. When the density of the detection toner image 18 corresponding to the detection pattern 17 having a small black area ratio is lower than the density reference value, in step 10, for example, the exposure amount is decreased and the development potential is increased. As described above, the CPU 6 controls the exposure amount control unit 8 and the developing bias power source 7.

According to the above first embodiment, as shown in FIG. 2, the curve (i) in the state before the change is changed to the curve (j) by lowering the charging potential, and the original in the high density portion is changed. The density reproduction range is expanded from C to C '. Further, by decreasing the exposure amount, the curve (j) before the change is changed to the curve (k), and the original density reproduction width in the low density portion is C
To C ''. Therefore, it is possible to prevent the image from being crushed in a portion having a large black area ratio, and to improve the reproducibility of the high density portion. In addition, it is possible to prevent image loss in a portion having a small black area ratio, and to improve reproducibility in a low density portion.

Next, the second embodiment will be described. First
The difference from the embodiment is that the detection toner images 16 and 18 corresponding to the detection pattern 15 having a large black area ratio and the detection pattern 17 having a small black area ratio are formed in the same step, and further, the charging potential and exposure are performed. The point is that the amount and the developing bias voltage are controlled in the same step.
Hereinafter, description will be given along the control flowchart of FIG.
First, the photo mode is selected in step 1, and step 2
When the copy button is pressed in step 3, the detection toner image 16 corresponding to the detection pattern 15 having a large black area ratio and the detection toner image 18 corresponding to the detection pattern 17 having a small black area ratio are exposed in step 3. It is formed on the surface of the body drum 1. Next, in step 4, the toner adhesion amount of the detection toner images 16 and 18 is detected by the P sensor, and in step 5, the comparison between the density of the detection toner images 16 and 18 and a preset density reference value is controlled. -It is performed by the CPU 6 which is the arithmetic unit. When the density of the detection toner image 16 corresponding to the detection pattern 15 having a large black area ratio is higher than the density reference value, in step 6, for example, the CPU 6 causes the charging high-voltage power supply 9 to lower the charging potential. To control. Further, when the density of the detection toner image 18 corresponding to the detection pattern 17 having a small black area ratio is lower than the density reference value, in the same step 6, for example, the exposure amount is decreased and the development potential is reduced. Exposure amount controller 8 and developing bias power source 7
To control.

According to the above-described second embodiment, it is possible to prevent image crushing in a portion having a large black area ratio with a smaller number of control steps than in the first embodiment, and to reproduce a high density portion. The quality is good. In addition, it is possible to prevent image loss in a portion having a small black area ratio, and to improve reproducibility in a low density portion.

Next, a third embodiment will be described. In the conventional copying machine provided with the photographic mode, the image density cannot be controlled according to the difference in the number of lines of the original. Therefore, in the third embodiment, different photo modes can be selected according to the document type, for example, the difference in the number of lines, and a plurality of detection toner images of different types are set corresponding to each photo mode. It has become so. For example, the photograph mode is set as follows for different print lines of the photograph original. Photo mode 1: Coarse original with few lines Photo mode 2: Normal original Photo mode 3: Fine original with many lines And used for controlling image forming process conditions for the above photo modes 1, 2 and 3. The number of lines of the detection pattern is 75 lines, 133 lines, 175 lines, or 100 lines, respectively.
Line, 133 line, 150 line, or 100 line, 150
Lines, 200 lines, etc. are assigned and set. here,
The number of lines means the number of halftone dots per inch in a halftone dot printed matter.

The control will be described below with reference to the flow chart of FIG. First, in step 1, for example, in the case of a fine-grained photo original, the photo mode 3 is selected, and step 2
Then, when the copy button is pressed, in step 3, a detection toner image 16 corresponding to the detection pattern 15 having a large black area ratio is formed on the surface of the photosensitive drum 1. next,
In step 4, the toner adhesion amount of the detection toner image 16 is detected by the P sensor, and in step 5, the detection toner image 1 is detected.
The CPU 6 as a control / calculation unit compares the density of 6 with a preset density reference value. When the density of the detection toner image 16 corresponding to the detection pattern 15 having a large black area ratio is higher than the density reference value, in step 6,
For example, the CPU 6 controls the charging high-voltage power supply 9 so as to reduce the charging potential.

Next, at step 7, a detection toner image 18 corresponding to the detection pattern 17 having a small black area ratio is formed on the surface of the photosensitive drum 1. Then in step 8,
The toner adhesion amount of the detection toner image 18 is detected by the P sensor, and in step 9, the density of the detection toner image 18 is compared with a preset density reference value by the CPU 6 which is a control / calculation unit. When the density of the detection toner image 18 corresponding to the detection pattern 17 having a small black area ratio is lower than the density reference value, in step 10, for example, the exposure amount is reduced and the development potential is increased. As described above, the CPU 6 controls the exposure amount control unit 8 and the developing bias power source 7.

According to the third embodiment described above, even in the case of photographic originals having different numbers of lines, it is possible to prevent the image from being crushed in the portion having a large black area ratio, and the reproducibility of the high density portion is improved. In addition, it is possible to prevent image loss in a portion having a small black area ratio, and to improve reproducibility in a low density portion.

A dot pattern can be used as the detection pattern in the above embodiment. According to this, it is possible to control the image density in response to changes over time and changes in the environment of halftone images (gray scale, etc.) having different black area ratios.

A line pattern can be used as the detection pattern in the above embodiment. According to this, it is possible to control the image density according to changes over time and environmental changes of line images (gray scale, etc.) having different black area ratios.

[0030]

According to the first aspect of the present invention, when the reproducibility of the image density is changed due to the influence of a change with time such as deterioration of the image carrier or an environmental change, this change is corrected. As described above, the image forming process conditions, for example, the charging potential, the exposure amount, the developing bias voltage, etc. are changed and set. Therefore, in the halftone image mode, it is possible to control changes in image density due to changes over time in the device, environmental changes, etc.
There is an excellent effect that the reproducibility of halftone image density becomes good.

According to the second aspect of the present invention, the detection patterns having different ratios can be used for density control in the areas of the image corresponding to the respective ratios.
Therefore, in the above-mentioned halftone image mode, it is possible to control changes over time in images (grayscale etc.) having different ratios and changes in image density due to environmental changes, and it is excellent that the reproducibility of halftone image density is improved. There is an effect.

According to the third aspect of the present invention, the document density in the image area having the large ratio can be faithfully reproduced. Therefore, in the above-mentioned halftone image mode, it is possible to control the change of the image density in the high density portion due to the time-dependent change of the apparatus, the environmental change and the like, and there is an excellent effect that the reproducibility of the halftone image density becomes good.

According to the fourth aspect of the invention, the original density in the image area having the small ratio can be faithfully reproduced. Therefore, in the above-mentioned halftone image mode, it is possible to control the change of the image density in the low density portion due to the change of the apparatus over time, the environmental change, etc., and there is an excellent effect that the reproducibility of the halftone image density becomes good.

According to the fifth aspect of the invention, even if the reproducibility of the image density changes due to the influence of the type of the original document, for example, the difference in the number of lines, this change is corrected and the image density does not change. As described above, the image forming process conditions, for example, the charging potential, the exposure amount, the developing bias voltage, etc. are changed and set. Therefore, it is possible to control changes in the image density due to changes in the image (gray scale, etc.) with different ratios depending on the type of document, such as the difference in the number of lines, and changes in the image density, and to reproduce halftone image density. There is an excellent effect that the property is further improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a copying machine according to an embodiment.

FIG. 2 is a characteristic diagram showing a relationship between a photosensitive member surface potential and a document density when the charging potential and the exposure amount change.

FIG. 3 is a flowchart of control according to the first embodiment.

FIG. 4 is a flowchart of control according to the second embodiment.

FIG. 5 is a flowchart of control according to the third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Charging device 3 Digital optical system 4 Developing device 5 P sensor 6 CPU 7 Development bias power source 8 Exposure amount control section 9 High voltage power source for charging 15, 17 Detection pattern 16, 18 Toner image for detection

Claims (5)

[Claims] 1. A charging means for uniformly charging the surface of an image carrier,
An exposing unit that forms an electrostatic latent image on the surface of the image bearing member by optical writing and a developing unit that forms a toner image corresponding to the electrostatic latent image on the surface of the image bearing member are provided, and an image with a halftone density is formed. In an image forming apparatus having a halftone image forming mode preset to apply an image forming process condition for reproduction, a toner density detecting unit for detecting a toner adhesion amount of the toner image is provided, A control means is provided for forming a detection toner image corresponding to a predetermined detection pattern on the body surface, and changing the image forming process condition based on the density of the detection toner image detected by the toner density detection means. An image forming apparatus characterized by the above. 2. The image forming apparatus according to claim 1, wherein a plurality of detection patterns having different ratios of the toner adhesion area to the entire area of the detection pattern are used as the detection patterns. 3. A control means for changing at least the charging potential of the charging means when the density of the detection toner image corresponding to the detection pattern having a large ratio is higher than a preset reference density. The image forming apparatus according to claim 2, wherein 4. A control means is provided for changing at least the exposure amount of the exposure means when the density of the detection toner image corresponding to the detection pattern having a small ratio is lower than a preset reference density. The image forming apparatus according to claim 2, wherein 5. A plurality of halftone image forming modes are set according to the type of original, and different types of detection patterns are used corresponding to the respective halftone image forming modes. The image forming apparatus according to claim 2.