JP2006126747A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus of high picture quality that improves gradation properties by preventing a white void part from being formed in a character in a half-tone image or at a periphery of a solid image and gradation reproducibility from deteriorating, and suppressing edge effect. <P>SOLUTION: A charging voltage of a charging device 2 and a developing bias voltage of a developing bias power source 11 are so set that when a latent image potential value of a test latent image and a developing current integral value are detected, the difference (potential difference) between the latent image potential value and developing bias voltage is varied in steps. Then the latent image potential value and developing current integral value are detected under conditions wherein the potential difference is different in steps, a linear expression formed from the developing current integral value corresponding to the potential difference is found for each of the solid latent image and a dot latent image, and development conditions are set to proper values so that the gradient of the linear expression becomes small. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrostatic recording image forming apparatus, and in particular, an image having a multicolor mode in which a multicolored developed image is formed on an image carrier and the developed images are collectively transferred to a transfer material. The present invention relates to a forming apparatus.

  In recent years, there has been an increasing demand for image quality and colorization in image forming apparatuses. Graininess, gradation, and sharpness are listed as evaluation standards for image quality. In order to be evaluated for high image quality, it is necessary to form a toner image that is faithful to the latent image.

  The so-called edge effect occurs in the two-component development method using the currently mainstream toner and carrier. The edge effect is a reduction in which the density is high at the periphery of an image with a large area and the density is low at the center. This edge effect is effectively used for emphasizing fine lines in a monochrome document output from a monochrome machine. However, in color originals output from color machines, the ratio of line / character images and solid patches existing on halftone images of color originals is higher than that of black and white originals, and both line images and area images are handled equally. A bad image is formed due to the effect.

  In color originals, graininess, gradation, and sharpness are listed as image quality evaluation criteria. In order to be evaluated as high image quality, these evaluation criteria need to be at a high level. When the effect occurs, the gradation is adversely affected. Therefore, it is necessary to reduce the edge effect as much as possible in the color machine.

  In order to suppress the edge effect and control the image density, the conventional image forming apparatus detects the reflection density of the toner moved from the developing roller onto the surface of the photosensitive member by using a reflection type photosensor. Control was performed based on the detection result. In this case, in order to detect the amount of toner adhering to the photosensitive member by the reflection density, it is necessary to obtain this reflection relationship in advance, but this relationship differs in the reflection component depending on the toner colorant. In general, it is difficult and complicated to handle because the detection sensitivity of the sensor itself varies, and the sensitivity of the sensor detection surface decreases due to contamination by foreign matters such as toner and paper dust.

As another technique, the toner charge amount of the latent image on the developing roller is detected as a moving charge amount / toner development amount, and an image density is adjusted by setting an optimum developing bias condition based on the detected toner charge amount. Proposed. (For example, patent document 1).
JP-A-6-27778

  However, in the technique of Patent Document 1, when the latent image used when setting the optimum developing bias condition is a patch latent image, the line image cannot be optimized and the image has an edge effect. White spots may occur in the vicinity of characters or solid images existing on a halftone image, and gradation reproducibility may deteriorate.

  The present invention prevents the occurrence of white spots around characters and solid images existing on a halftone image and the deterioration of gradation reproducibility, suppresses the edge effect, and improves the gradation. An object of the present invention is to provide a simple image forming apparatus.

  The invention described in claim 1 includes a charging means for charging a photoconductor, an exposure means for exposing the photoconductor to form an electrostatic latent image, and charging toner to the electrostatic latent image on the photoconductor. The developing means for forming a toner image, the potential detecting means for detecting the potential of the electrostatic latent image on the photosensitive member, and the developing toner flowing at the time of development by the charged toner moving from the developing device onto the photosensitive member at the time of development. A current detection means for detecting current; the charging means; the exposure means; the developing means; the potential detection means; and a control means for controlling the current detection means; The image forming apparatus is characterized in that an optimum developing condition is set according to a condition obtained from a detection value detected by a potential detection means and a detection value detected by the current detection means.

  According to a second aspect of the present invention, in the first aspect of the present invention, the control unit continuously includes a solid latent image that is continuous in a predetermined area in the main scanning and sub-scanning directions when the optimum development condition is set. A dot latent image not formed is formed as an electrostatic latent image on the exposure means.

  According to a third aspect of the present invention, in the first or second aspect of the invention, the control unit is applied to a developing bias voltage applied to a developing roller of the developing unit or the charging device when the optimum developing condition is set. The charging voltage is changed, and the potential difference between the developing bias voltage and the electrostatic latent image is set stepwise.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects of the present invention, the control means converts the line format obtained from the detected current value corresponding to the potential difference to the solid latent image. The optimum development conditions are set for each of the dot latent images and set so that the inclination of the linear format becomes small.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the control means optimizes the development conditions by controlling the peak value of the AC component of the development bias voltage. It is characterized by.

  The invention according to claim 6 is the invention according to any one of claims 1 to 4, wherein the control means optimizes the developing condition by controlling the frequency of the AC component of the developing bias voltage. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

  According to a seventh aspect of the present invention, in the invention according to any one of the first to fourth aspects, the control means optimizes the development conditions by controlling the duty ratio of the waveform of the AC component of the development bias voltage. It is characterized by becoming.

  According to an eighth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the control means optimizes the development conditions by setting the number of rotations of the developing roller. To do.

  The invention according to claim 9 is the invention according to any one of claims 1 to 4, wherein the control means optimizes the developing condition by controlling a distance between the developing roller and the photoconductor. It is characterized by doing.

  According to a tenth aspect of the present invention, in the invention according to any one of the first to ninth aspects, the control unit is configured so that the toner adhesion amount of the photoconductor becomes a desired value after the optimum development condition is set. In addition, the DC value of the developing bias voltage is controlled.

  According to an eleventh aspect of the present invention, in the invention according to any one of the first to ninth aspects, the amount of toner adhesion on the photoconductor becomes a desired value after the optimum development condition is set. As described above, the toner density of the developing means is controlled.

  According to the present invention, since the optimum development condition is set according to the condition obtained from the detection value detected by the potential detection means and the detection value detected by the current detection means, the character or solid image existing on the halftone image is set. It is possible to form a high-quality image in which peripheral white spots are prevented and gradation reproducibility is prevented, edge effects are suppressed, and gradation is improved.

  The configuration of the image forming apparatus according to the present embodiment will be described with reference to the drawings. FIG. 1 shows a configuration of a writing unit of the image forming apparatus of the present embodiment. The writing unit includes a photoreceptor 1, a charging device 2, a laser writing device 3, a developing device 4, a transfer roller 5, and a surface potential detection device 11. The developing device 4 has a developing roller 8 and is connected to a developing bias power source 10. A current integrator 9 is connected to the developing bias power source 10. The current integrating device 9 performs time integration of the amount of current flowing through the photosensitive member 1 during development.

  The photoreceptor 1 is charged by the charging device 2. The charged photoconductor 1 is exposed by a laser beam 7 output from the laser writing device 3, and an electrostatic latent image is formed on the photoconductor 1. By using the developing roller 8 to which the developing bias voltage is applied by the developing bias power source 10, toner is attached to the photosensitive member 1, whereby the electrostatic latent image is visualized. At this time, the current integrating device 9 detects the amount of current flowing through the photosensitive member 1 by time integration. Further, the surface potential detector 11 detects the potential of the electrostatic latent image on the photoreceptor 1. The toner image on the photoreceptor 1 is transferred onto the printing paper 6 by the transfer roller 5. Thereafter, the photosensitive member 1 is discharged and cleaned by the photosensitive member cleaning device and the discharging roller.

  Note that overall control of the writing unit and control of each component are performed by the main control unit of the image forming apparatus.

  In the image forming apparatus of the present embodiment, the main control unit develops according to the condition obtained from the latent image potential value obtained from the surface potential detection device 11 and the development current integration value obtained from the current integration device 9. Set the condition to an appropriate value. This will be specifically described below.

  First, in order to set the development condition to the optimum value, a test composed of a solid latent image (patch latent image) that is continuous in a predetermined area in the main scanning / sub-scanning direction and a dot latent image that is not continuous. Using the latent image, a latent image potential value and a development current integrated value for the test latent image are detected. This test latent image is formed on the photoreceptor 1 by the laser writing device 3. As an example of the test latent image, a solid latent image is a 2 × 2 cm latent image and a dot latent image is a latent image composed of a 2 × 2 dot image of 600 dpi. Instead of the dot latent image, it is also possible to use a line latent image that is continuous in the main scanning direction or the sub-scanning direction and is composed of 2-dot horizontal lines and vertical lines.

  When detecting the latent image potential value and the development current integrated value of the test latent image, the main control unit changes the difference (potential difference) between the latent image potential value and the development bias voltage stepwise. The charging voltage and the developing bias voltage of the developing bias power source 11 are set. Then, the latent image potential value and the development current integrated value are detected under a condition in which the potential difference varies stepwise. Then, the main control unit obtains the line format obtained from the development current integrated value corresponding to the potential difference for each of the solid latent image and the dot latent image, and sets the development condition to an appropriate value so that the inclination of the line format becomes small.

  Here, as a method of setting the development condition to an appropriate value, a method of changing the peak value of the AC component of the development bias, a method of changing the frequency of the AC component (AC component) of the development bias, There is a method of changing the duty ratio of the waveform. Further, the developing condition can be set to an appropriate value also by a method of changing the rotation speed of the developing roller 9 or a method of changing the distance between the opposing surfaces of the developing roller 9 and the photosensitive member 1.

  After setting the developing condition to an appropriate value using the above method, the main control unit sets the DC value of the developing bias voltage and the toner of the developing device 4 so that the toner adhesion amount on the photoreceptor 1 becomes a desired value. Change or adjust the density. As a result, the toner adhesion amount on the photosensitive member 1, that is, the image density of the output image can be changed, so that the image density of the output image can be set to a desired density.

  According to the present embodiment, it is possible to prevent the occurrence of white spots around characters and solid images existing on a halftone image and the deterioration of gradation reproducibility, and to improve gradation. Hereinafter, changes in various image quality after optimization of the development conditions according to the present embodiment will be described with reference to the drawings.

  FIG. 2 shows the amount of white spots around characters and solid images existing on the halftone image. Comparing the amount of white spots before the development conditions are optimized and after the development conditions are optimized, it can be seen that the amount of white spots is reduced after the development conditions are optimized. Thus, the occurrence of white spots can be suppressed by optimizing the development conditions of the present embodiment.

  FIG. 3 shows the resolving power of a single line (6 cycles / mm). The resolving power represents the lightness amplitude, and the higher the lightness amplitude of the black line and the white line, the higher the resolution. Comparing the resolving power before optimization of the development conditions and after optimization of the development conditions, it can be seen that the resolution is improved after the optimization of the development conditions. As described above, the image resolving power can be increased by optimizing the developing conditions of this embodiment.

FIG. 4 shows tone reproducibility for known input data. In FIG. 4, since the lightness is higher after optimization of the development conditions at the same input value, the gradation reproducibility is better after optimization of the development conditions before and after optimization of the development conditions. You can see that Further, when the contribution ratio r ² of the input value and the brightness is calculated, it is 0.937 after the optimization and 0.827 before the optimization, which shows that the gradation reproducibility is excellent. As described above, the gradation reproducibility of the image can be increased by optimizing the development conditions of the present embodiment.

2 is a block diagram illustrating a configuration of a writing unit of the image forming apparatus according to the present exemplary embodiment. FIG. It is a graph showing the amount of white spots before and after development condition optimization. It is a graph showing the resolving power of an image before and after development condition optimization. It is a graph showing the gradation reproducibility of an image before and after development condition optimization.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging device 3 Laser writing device 4 Developing device 8 Developing roller 9 Current integrating device 10 Developing bias power source 11 Surface potential detecting device

Claims (11)

Charging means for charging the photoreceptor;
Exposure means for exposing the photoreceptor to form an electrostatic latent image;
Developing means for forming a toner image by attaching charged toner to the electrostatic latent image on the photoreceptor;
A potential detecting means for detecting a potential of the electrostatic latent image on the photoreceptor;
Current detecting means for detecting a developing current flowing at the time of development by charge toner moving from the developing device to the photosensitive member at the time of development;
A control means for controlling the charging means, the exposure means, the developing means, the potential detection means, and the current detection means;
The image forming apparatus, wherein the control unit sets an optimum developing condition according to a condition obtained from a detection value detected by the potential detection unit and a detection value detected by the current detection unit.   The control unit forms a solid latent image continuous in a predetermined area in the main scanning and sub-scanning directions and a non-continuous dot latent image on the exposure unit as an electrostatic latent image when the optimum development condition is set. The image forming apparatus according to claim 1, wherein:   The control unit changes a developing bias voltage applied to a developing roller of the developing unit or a charging voltage applied to the charging device when the optimum developing condition is set, and a potential difference between the developing bias voltage and the electrostatic latent image. The image forming apparatus according to claim 1, wherein the image forming apparatus is set stepwise.   The control means obtains a line format obtained from the detected current value corresponding to the potential difference for each of the solid latent image and the dot latent image, and sets optimum development conditions so that the inclination of the line format becomes small. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   5. The image forming apparatus according to claim 1, wherein the control unit optimizes a development condition by controlling a peak value of an AC component of the development bias voltage. 6.   5. The image forming apparatus according to claim 1, wherein the control unit optimizes development conditions by controlling a frequency of an AC component of the development bias voltage. 6.   5. The image forming apparatus according to claim 1, wherein the control unit optimizes a development condition by controlling a duty ratio of a waveform of an AC component of the development bias voltage. 6.   5. The image forming apparatus according to claim 1, wherein the control unit optimizes a developing condition by setting a rotation number of the developing roller. 6.   The image forming apparatus according to claim 1, wherein the control unit optimizes a developing condition by controlling a distance between the developing roller and the photoconductor.   10. The control unit according to claim 1, wherein the control unit controls a DC value of the developing bias voltage so that a toner adhesion amount of the photosensitive member becomes a desired value after the optimum developing condition is set. 2. The image forming apparatus according to item 1.   10. The control unit according to claim 1, wherein the control unit controls a toner density of the developing unit so that a toner adhesion amount on the photoconductor becomes a desired value after the optimum development condition is set. 2. The image forming apparatus according to item 1.

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